Disorders Of Nerve Roots And Plexuses

Question 1

What kind of nerve fibers are contained in a) dorsal roots and b) ventral roots

Answer 1

a) The dorsal roots contain sensory fibers that are central processes of the pseudo-unipolar neurons of the DRG. On reaching the spinal cord, these fibers either synapse with other neurons in the posterior horn or pass directly into the posterior columns.

b)
- Extensions of anterior horn motor neurons (alpha, beta, and gamma fibers)
- fibers of neurons in the intermediolateral horn (preganglionic sympathetic neurons found in lower cervical and thoracic segments)
- a population of unmyelinated and thinly myelinated axons that come from sensory and sympathetic ganglia

Question 2

Spinal roots numbers in relation with corresponding vertebral segment

Answer 2

Each cervical nerve root exits above its corresponding vertebral segment, with the sole exception being the C8 nerve root, which exits below C7 and above T1. At thoracic, lumbar, and sacral levels, each root exits below its corresponding vertebral level

Question 3

a) Which part of the spinal cord is more susceptible to avulsion and b) what kind of avulsion can occur (+ mechanism of action)

Answer 3

a) Avulsion at the level of the cervical roots

b) can be
i) total
ii) Erb–Duchenne palsy, in which the arm hangs at the side, internally rotated, and extended at the elbow because of paralysis of C5- and C6-innervated muscles (the supraspinatus and infraspinatus, deltoid, biceps). Injuries responsible for Erb–Duchenne palsy are those that cause a sudden and severe increase in the angle between the neck and shoulder, generating stresses that are readily transmitted in the direct line along the upper portion of the brachial plexus to the C5 and C6 roots (e.g. obstetrical, motor accidents etc)
iii) Dejerine–Klumpke palsy, in which there is weakness and wasting of the intrinsic hand muscles, with a characteristic claw-hand deformity due to paralysis of C8- and T1-innervated muscles. Dejerine–Klumpke palsy occurs when the limb is elevated beyond 90 degrees and tension falls directly on the lower trunk of the plexus, C8, and T1 roots. (e.g. fall from a height in which the outstretched arm grasps an object to arrest the fall, obstetrical etc)

Question 4

Nerve root avulsion a) clinical features and b) diagnosis

Answer 4

a) At the onset of root avulsion, flaccid paralysis and complete anesthesia develop in the myotomes and dermatomes served by ventral and dorsal roots, respectively.

b) Electrophysiological tests valuable in differentiating a root avulsion from traumatic plexus or nerve injury include the measurement of a sensory nerve action potential (SNAP) and needle EMG examination of the cervical paraspinal muscles.
In the setting of a dorsal root avulsion, the patient may experience complete anesthesia in the dermatome, yet the SNAP is reserved as the DRG cell bodies and the peripheral portions of their axons remain intact. *
Needle EMG of the cervical paraspinal muscles permits separation of damage of the plexus and of ventral root fibers because the posterior primary ramus, which arises just beyond the DRG and proximal to the plexus as the first branch of the spinal nerve, innervates these muscles. Thus, cervical paraspinal fibrillation potentials support the diagnosis of root avulsion

• An absent SNAP indicates sensory axon loss distal to the DRG but does not exclude coexisting root avulsion

Question 5

Are paraspinal fibrilation potentials always present in nerve root avulsion

Answer 5

No.
Paraspinal fibrillation potentials may be absent for two reasons. First, they do not appear for 7 to 10 days after the onset of axonotmesis, and second, even if the timing of the needle EMG is right, they may not be seen because of innervation of the paraspinal muscles from multiple segmental levels.

Question 6

Pathophysiology of disc herniation

Answer 6

With age, the fibers of the annulus fibrosus lengthen, weaken, and fray thereby allowing the disk to bulge posteriorly. In the setting of such changes, relatively minor trauma leads to further tearing of annular fibers and ultimately to herniation of the nucleus pulposis

Question 7

Types of lumbar disc herniation

Answer 7

Reinforcing the annulus fibrosus posteriorly is the posterior longitudinal ligament, which in the lumbar region is dense and strong centrally and less well developed in its lateral portion.
Because of this anatomical feature, the direction of lumbar disk herniations tends to be posterolateral, compressing the nerve roots in the lateral recess of the spinal canal.
Less commonly, more lateral (foraminal) herniations compress the nerve root against the vertebral pedicle in the intervertebral foramen

Question 8

Types of cervical disc herniation

Answer 8

Most cervical disk herniations are posterolateral

or foraminal

Question 9

Spondylosis: a) characteristics and b) consequences

Answer 9

a) osteoarthritic changes in the joints of the spine, the disk per se (desiccation and shrinkage of the normally semisolid, gelatinous nucleus pulposus), and the facet joints
b) Because it spawns osteophyte formation, spondylosis leads to compromise of the spinal cord in the spinal canal and the nerve roots in the intervertebral foramina. Restriction in the dimensions of these bony canals may be exacerbated by thickening and hypertrophy of the ligamentum flavum, which is especially detrimental in patients with congenital cervical or lumbar canal stenosis

Question 10

Disc herniation: clinical features

Answer 10

Root compression from disk herniation gives rise to a distinctive clinical syndrome that in its fully developed form comprises

1) radicular pain
Nerve root pain is variably described as knifelike or aching and is widely distributed, projecting to the sclerotome (defined as deep structures such as muscles and bones innervated by the root). Typically, root pain is aggravated by coughing, sneezing, and straining at stool (actions that require a Valsalva maneuver and raise intraspinal pressure).

2) dermatomal sensory loss
Sensory loss caused by the compromise of a single root may be difficult to ascertain because of the overlapping territories of adjacent roots, although loss of pain is usually more easily demonstrated than loss of light touch sensation
3) weakness in the myotome
4) reduction or loss of the deep tendon reflex subserved by the affected root.

Question 11

Which sign can help differentiate pain coming from compressed nerve root and spondylotic facet joints

Answer 11

paresthesias referred to the specific dermatome, especially to the distal regions of the dermatomes

Question 12

Which levels are most commonly affected in disc herniation of the lumbosacral region

Answer 12

95% of disk herniations occur at the L4–L5 or L5–S1 levels

Question 13

Which nerve roots are most commonly affected in posterolateral lumbar disc herniations

Answer 13

the posterolateral disk herniation compresses the nerve root passing through the foramen below that disk, so L4–L5 and L5–S1 herniations usually produce L5 and S1 radiculopathies, respectively

Question 14

Clinical features of S1 radiculopathy

Answer 14

In an S1 radiculopathy, pain radiates to the buttock and down the back of the leg (classic sciatica), often extending below the knee; paresthesias are generally felt in the lateral ankle and foot. The ankle jerk is generally diminished or lost, and weakness may be detected in the plantar flexors, knee flexors and hip extensors

Question 15

Clinical feature of O5 radiculopathy

Answer 15

In an L5 radiculopathy paresthesias are felt on the dorsum of the foot and the outer portion of the calf. The ankle reflex is typically normal, but there may be reduction of the medial hamstring reflex. Weakness may be found in L5-innervated muscles served by the peroneal nerve (including the extensor hallucis longus, tibialis anterior and peronei), tibial nerve (tibialis posterior) and the superior gluteal nerve (including gluteus medius). Weakness may be restricted to the extensor hallucis longus, or be more extensive and involve the tibialis anterior, resulting in foot drop

Question 16

Tests for O5 and I1 radiculopathy

Answer 16

A positive straight leg–raising test result is a sensitive indicator of L5 or S1 nerve root irritation. The test is deemed positive when the patient complains of pain radiating from the back into the buttock and thigh with leg elevation to less than 60 degrees
A less sensitive but highly specific test is the crossed straight leg–raising test when the patient complains of radiating pain on the affected side with elevation of the contralateral leg

Question 17

Clinical features of O4 radiculopathy

Answer 17

Pain and paresthesias along the medial aspect of the knee and lower leg. The patellar reflex is diminished, and weakness may be noted in the quadriceps and hip adductors (innervated by the femoral and obturator nerves, respectively).

Question 18

What is cauda equina syndrome

Answer 18

When large herniations occur in the midline at either the L4–L5 or the L5–S1 level, many of the nerve roots running past that level to exit through intervertebral foramina below that level may be compressed, producing the cauda equina syndrome of bilateral radicular pain, paresthesias, weakness, attenuated reflexes below the disk level, and urinary retention. This is a surgical emergency requiring urgent decompression

Question 19

Clinical features of C6 and C5 radiculopathy

Answer 19

Pain at the tip of the shoulder radiating into the upper part of the arm, lateral side of the forearm, and thumb. Paresthesias are felt in the thumb and index finger. The brachioradialis and biceps reflexes are attenuated or lost. Weakness may occur in the muscles of the C6 myotome supplied by several different nerves, including the biceps (musculocutaneous nerve), deltoid (axillary nerve), and pronator teres (median nerve).

The clinical features of C5 radiculopathies are similar, except that the rhomboids and spinatus muscles are more likely to be weak.

Question 20

Clinical features of C7 and C8 radiculopathy

Answer 20

In A7 radiculopathy, pain radiates in a wide distribution to include the shoulder, chest, forearm, and hand. Paresthesias involve the dorsal surface of the middle finger. The triceps reflex is usually reduced or absent. A varying degree of weakness usually involves one or more muscles of the C7 myotome, especially the triceps the flexor carpi radialis and the pronator teres.

Less common C8 root involvement presents a similar clinical picture with regard to pain. Paresthesias, however, are experienced in the fourth and fifth digits, and weakness may affect the intrinsic muscles of the hand, including finger abductor and adductor muscles (ulnar nerve), thumb abductor and opponens muscles (median nerve), finger extensor muscles (posterior interosseus branch of the radial nerve), and flexor pollicis longus (anterior interosseus branch of the median nerve)

Question 21

a) Diagnosis of radiculopathy.

b) Are all the tests positive in all patients

Answer 21

a) Diagnosis is aided by a variety of imaging techniques
(e.g., plain radiography, myelography, CT myelography,
MRI) and EMG testing

b) Both diagnostic modalities—the imaging approach that reveals anatomical details and the EMG techniques
that disclose neurophysiological function—agree in the majority of patients (60%) with a clinical history compatible with cervical or lumbosacral radiculopathy, although only the results of one study will be positive in a significant minority of patients (40%)

Question 22

Is plain radiography useful in diagnosis of radiculopathy

Answer 22

Although plain radiography is unhelpful in the identification of a herniated disk per se, in both the cervical and the lumbar area, it reveals spondylotic changes when present. It also may be useful for identifying less common disorders that produce radicular symptoms and signs: bony metastases, infection, fracture, and spondylolisthesis, for example

Question 23

Which is the best imaging method for a) cervical and b) lumbar radiculopathy

Answer 23

a) In the cervical region, the best methods for assessing the relationship between neural structures (spinal cord and nerve root) and their fibro-osseous surroundings (disk, spinal canal, and foramen) are postmyelography CT (unenhanced CT reveals little more than the presence of bony changes) and MRI. MRI is equivalent in diagnostic capacity to postmyelography CT and therefore is preferred.
b) In the lumbosacral region, CT is an effective method for evaluating disk disease, but when available, MRI is considered the superior imaging study. Its excellent resolution, multiplanar imaging, the ability to see the entire lumbar spine including the conus, and the absence of ionizing radiation make it highly sensitive in detecting structural radicular disorders

Question 24

In which exception there is reduction in SNAP in a radiculopathy

Answer 24

In the specific instance of L5 radiculopathy, because the L5 DRG may reside proximal to the neural foramen, if intraspinal pathology is severe enough, compression of the L5 DRG may lead to attenuation or loss of the superficial peroneal nerve SNAP

Question 25

Which is the most udeful diagnostic procedure in the evaluation of radiculopathy and what are the findings

Answer 25

Needle EMG is the most useful electrodiagnostic procedure in the diagnosis of suspected radiculopathy. A study is considered positive if abnormalities— especially acute changes of denervation including fibrillation potentials and positive sharp waves—are present in two or more muscles that receive innervation from the same root, preferably via different peripheral nerves. No abnormalities should be detected in muscles innervated by the affected root’s rostral and caudal neighbors.
Reduced motor unit potential (MUP) recruitment (manifested by decreased numbers of MUPs firing at an increased rate) and MUP abnormalities of reinnervation (high-amplitude, increased duration, polyphasic MUPs) are also sought by the needle electrode but are not as reliable as fibrillation potentials in establishing a definitive diagnosis of radiculopathy

Question 26

Does absence of fibrillation potentials exclude the diagnosis of radiculopathy

Answer 26

Absence of fibrillation potentials does not, however, exclude the diagnosis of radiculopathy. Two main reasons for this exist.
First, examination in the first 1 to 3 weeks after onset of nerve root compromise may be negative because it takes approximately 2 weeks for these potentials to appear. At the early stages in the process of nerve root compression, the only needle electrode examination manifestation of radiculopathy might be reduced MUP recruitment resulting from axon loss, focal demyelination with conduction block, or both.
Second, fibrillation potentials disappear as denervated fibers are reinnervated by axons of the same or an adjacent myotome beginning 2 to 3 months after nerve root compression. Thus in the later phases of nerve root compression, the only needle EMG changes indicative of radiculopathy might be chronic neurogenic changes of reduced recruitment and MUP remodeling

Question 27

Distribution of fibrillation potentials in C5, C6 and C7 radiculopathy

Answer 27

The distribution of fibrillation potentials is relatively stereotyped for C5, C7, and C8 radiculopathies, whereas C6 radiculopathy has the most variable presentation. In about half of patients, the findings are similar to C5 radiculopathy, whereas in the other half, findings are identical to C7 radiculopathy

Question 28

Indications for surgical treatment in cervical radiculopathy

Answer 28

1) if there is unremitting pain despite an adequate trial of conservative management
2) if there is progressive weakness in the territory of the compromised nerve root
3) if there are clinical and radiological signs of an accompanying new onset of myelopathy

Question 29

Indications for surgical treatment of in lumbar radiculopathy

Answer 29

1) in patients presenting with cauda equina syndrome, for which surgery may be required urgently
2) if the neurological deficit is severe or progressing
3) if severe radicular pain continues after 4 to 6 weeks of conservative management

Question 30

Symptoms and signs in diabetic thoracoabdominal polyradiculoneuropathy

Answer 30

The presenting symptoms are generally pain and paresthesias of rapid onset in the abdominal and chest wall. The trunk pain may be severe, described variably as burning, sharp, aching, and throbbing. It may mimic the pain of acute cardiac or intra-abdominal medical emergencies and may simulate disk disease, but the rarity of thoracic disk protrusions and the usual development of a myelopathy help exclude this diagnosis.
Findings of diabetic thoracoabdominal polyradiculoneuropathy include heightened sensitivity to light touch over affected regions; patches of sensory loss on the anterior, lateral, or posterior aspects of the trunk; and unilateral abdominal swelling due to localized weakness of the abdominal wall muscles
In 30% to 50% of patients, the disorder is preceded by substantial weight loss of 30 to 40 pounds

Question 31

Symptoms and signs in diabetic lumbosacral polyradiculoneuropathy

Answer 31

Diabetic lumbosacral polyradiculoneuropathy involves the legs, especially the anterior thighs, with pain, dysesthesia, and weakness, reflecting the major involvement of upper lumbar roots. Motor, sensory, and autonomic fibers are all affected by the disease process. In most patients, onset is fairly abrupt, with symptoms developing over days to a couple of weeks. Early in the course of the condition, the clinical findings are usually unilateral and include weakness of muscles supplied by L2–L4 roots (iliopsoas, quadriceps, and hip adductors), reduced or absent patellar reflex, and mild impairment of sensation over the anterior thigh. As time passes, there may be territorial spread (proximal, distal, or contralateral involvement as the polyradiculoneuropathy evolves).
Worsening may occur in a steady or a stepwise fashion, and it may take several weeks to progress from onset to peak of the disease. At its peak, weakness varies in severity and extent from a mildly affected patient with slight unilateral thigh weakness to a profound degree of bilateral leg weakness in the territory of the L2–S2 nerve roots.

Question 32

Symptoms and signs in diabetic cervical polyradiculoneuropathy

Answer 32

May occur independently or in temporal association with lumbosacral polyradiculoneuropathy.
Similar to the lumbosacral form, it is characterized as an acute or sub-acute onset of unilateral limb pain, followed by focal hand and forearm weakness that may then progress to involve multiple myotomes or focal nerve territories in the affected limb.
Though less common than the polyradiculoneuropathy of lumbosacral onset, progression to the contralateral upper extremity is seen in up to 35% of patients, and involvement of cranial, thoracic, and lumbosacral regions may also occur

Question 33

Paraclinical tests for the diagnosis of diabetic polyradiculoneuropathy

Answer 33

1) elevated fasting blood glucose in the majority of patients
2) erythrocyte sedimentation rate is usually normal (elevated in a subgroup of patients with lumbosacral polyneuroradiculopathy)
3) The typical electrodiagnostic findings comprise features of a sensorimotor axon-loss polyneuropathy (diminished sensory and motor action potentials, normal or slightly prolonged distal latencies, and normal or mildly slowed conduction velocities) with additional needle electrode examination findings of active and chronic denervation changes in paraspinal, pelvic girdle, and limb muscles. Taken together, the findings reflect multifocal axonal damage to the nerve roots and brachial or lumbosacral plexus. Although clinical findings may point to unilateral involvement, the electrodiagnostic examination generally discloses bilateral signs.
4) MRI of the brachial plexus in diabetic cervical polyradiculoneuropathy is typically abnormal with an increase in T2 signaling at the root, trunk, cord, or individual nerve level being the most common finding, often in a more extensive distribution than the clinical presentation would suggest. Nerve hypertrophy and increased T2 signal in muscle (suggestive of edema) were also observed. Both CT and myelography studies are typically normal.
5) The CSF protein level is usually increased to an average of 120 mg/dL, but in some patients values exceed 350 mg/dL
6) Biopsy of proximal nerve sensory branches reveals axon loss and demyelination; in more severely affected patients, inflammatory cell infiltration and vasculitis is found. Further studies of nerve biopsy specimens indicate that a microscopic vasculitis (involvement of small arterioles, venules, and capillaries) leads to ischemic injury, which in turn causes axonal degeneration and secondary segmental demyelination

Question 34

Natural history of diabetic polyradiculoneuropathy

Answer 34

The natural history of diabetic polyradiculoneuropathy is for improvement to occur in most patients, although the recovery phase is lengthy, ranging between 1 and 18 months with a mean of 6 months. Pain and dysesthesias improve or disappear entirely in 85% of patients; numbness improves or recovers in 50%; and strength is partially or completely restored in 70%. In some patients, episodes recur

Question 35

Treatment of diabetic polyradiculoneuropathy

Answer 35

Therapy is usually directed toward ameliorating the severe pain of this condition. The tricyclics, especially nortriptyline (with a better side-effect profile than amitriptyline), selective serotonin reuptake inhibitors (e.g., sertraline, nefazodone hydrochloride), selective serotonin and norepinephrine reuptake inhibitors (e.g., duloxetine, venlafaxine), anticonvulsants (e.g., gabapentin, pregabalin, carbamazepine), clonazepam, baclofen, clonidine, mexiletine, IV lidocaine, and topical capsaicin may have a role separately or in combination. Prospective studies have suggested a role for immunotherapy in the treatment plan of diabetic polyradiculoneuropathy where electrophysiological findings are those of CIDP, although the degree of improvement has been shown not to be as robust as in the immunotherapy of idiopathic CIDP

Question 36

Differential diagnosis of diabetic polyradiculoneuropathy

Answer 36

The major differential diagnostic considerations are polyradiculoneuropathies related to degenerative disk disease, infection, inflammatory or autoimmune mediated disease, and neoplastic processes. These can usually be excluded by history, examination, and routine laboratory investigations including CSF analysis

*The clinical presentation provoking the most anxiety is the frail elderly patient not known to be diabetic who has weight loss and abrupt onset of lower-extremity pain and weakness that progresses over months. In such a patient, the specter of neoplasia looms large, and thorough imaging studies of the nerve roots and plexuses are mandatory

Question 37

Clinical features of neoplastic polyradiculoneuropathy

Answer 37

The clinical features of neoplastic polyradiculoneuropathy include radicular pain, dermatomal sensory loss, areflexia, weakness of a lower motor neuron type, and bowel/ bladder dysfunction.
Often the distribution of the sensory and motor deficits is widespread and simulates a severe sensorimotor polyneuropathy. Associated clinical manifestations (e.g., nuchal rigidity, confusion, cranial polyneuropathies) result from infiltration of the meninges

Question 38

Paraclinical tests for the diagnosis of neoplastic polyradiculoneuropathy

Answer 38

1) The most revealing diagnostic procedure is lumbar puncture, which is almost always abnormal, disclosing one or more or the following: mononuclear pleocytosis, reduced CSF glucose, elevated protein, and neoplastic cells.
2) spinal fluid cytological analysis may be initially negative in more than one-third of patients who have compelling evidence of leptomeningeal carcinomatosis.
3) A sensitive, albeit nonspecific, electrophysiological indicator of nerve root involvement is an abnormal F wave. In the symptomatic patient with cancer, prolonged F-wave latencies or absent F responses should raise suspicion of leptomeningeal metastases. 4) Postmyelography CT adds strong evidence in support of the diagnosis if it demonstrates multiple nodular defects on the nerve roots, but spinal MRI, especially with gadolinium enhancement, is the initial test of choice in the cancer patient in whom leptomeningeal involvement of the spine is suspected. Approximately 50% of patients with neoplastic meningitis and spinal symptoms have abnormalities on these studies.
Gadolinium-enhanced MRI of the brain discloses abnormalities, including contrast enhancement of the basilar cisterns or cortical convexities and hydrocephalus.

Question 39

Treatment of neoplastic polyradiculoneuropathy

Answer 39

Standard therapy for neoplastic meningitis is essentially palliative; it does, however, afford stabilization and protection from further neurological deterioration. A multidisciplinary approach is recommended, with input from medical oncology, neuro-oncology, radiation oncology, and neurosurgery. With treatment that includes radiotherapy to sites of symptomatic disease, intrathecal or intraventricular chemotherapy (methotrexate, thiotepa, and cytosine arabinoside), and optimal management of the underlying malignancy, median survivals of 2 to 5 months may be achieved

Question 40

Natural history of herpes zoster infection

Answer 40

During primary infection, the virus colonizes the DRG and remains latent for many decades until it is reactivated, either spontaneously or when virus-specific cell-mediated immunity declines secondary to specific conditions (e.g., lymphoproliferative disorders, treatment with immunosuppressive drugs, organ transplant recipients, seropositivity for HIV) or normal aging, and travels down sensory nerves. Pathological changes, which are characterized by lymphocytic infiltration and variable hemorrhage, are found in the skin, DRG, and spinal roots. Involvement of the ventral roots and on occasion the spinal cord explains the development of motor signs in some patients

Question 41

Herpes zoster infection: clinical features

Answer 41

Herpes zoster is characterized by sharp or burning radicular pain associated with itching, numbness, dysesthesias (altered sensation), and/or allodynia (a painful response to normally non-noxious stimulation) typically in a single dermatome. The cutaneous eruption, unilateral and respecting the midline, begins as an erythematous maculopapular rash and progresses to grouped clear vesicles that continue to form for 3 to 5 days. These become pustules by 3 to 4 days and form crusts by 10 days. In the normal immunocompetent host, lesions resolve in 2 to 4 weeks, often leaving a region of reduced sensation, scarring, and pigmentation. Pain usually disappears as vesicles fade

Question 42

What is post herpetic neuralgia

Answer 42

Persistent severe pain that present for more than 30 days after rash onset or following cutaneous healing is termed postherpetic neuralgia. This complication is more likely to develop in the elderly, occurring in 50% of patients over 60 years of age. In half of patients affected with PHN, the pain resolves within 2 months, and 70% to 80% of patients are pain free by 1 year. Rarely, pain persists for years

Question 43

Is dissemination of herpes zoster infection possible

Answer 43

In the immunologically normal host, dissemination of the
virus is rare, occurring in fewer than 2% of patients.
In the immunocompromised patient, however, dissemination occurs in 13% to 50% of patients. Most often, spread is to distant cutaneous sites, but involvement of the viscera (lung, gastrointestinal tract, and heart) and CNS may occur. A serious complication of herpes zoster ophthalmicus is delayed contralateral hemiparesis caused by cerebral angiitis. The syndrome usually develops 1 week to 6 months after the onset of zoster and occurs in patients of all ages, 50% of whom are immunologically impaired. The mortality rate from cerebrovascular complications is 25%, and only approximately 30% of survivors recover fully.

Question 44

Complication of cutaneous herpes zoster

Answer 44

A complication of cutaneous herpes zoster is segmental
motor weakness, which occurs in up to 30% of patients with zoster reactivation. Segmental zoster paresis is about equally divided between the arms and legs, with predominantly proximal muscle weakness reflecting weakness in cervical and lumbar—C5, C6, and C7 or L2, L3, and L4—myotomes, respectively. The diaphragm and abdominal muscles may be affected, and bladder and bowel dysfunction may occur in the setting of lumbosacral zoster. The interval between skin eruption and paralysis is approximately 2 weeks, with a range of 1 day to 5 weeks and a rare instance reported of delayed (4.5 months) onset of diaphragmatic paralysis. Weakness peaks within hours or days and generally follows the dermatomal distribution of zoster eruptions. The prognosis for recovery is good, with nearly complete return of function in two-thirds of patients over the course of 1 to 2 years, 55% showing full recovery, and another 30% showing significant improvement. One in five patients is left with severe and permanent residua.

Question 45

Treatment of herpses zoster

Answer 45

The major goals of treatment are to relieve local discomfort, prevent dissemination, and reduce the severity of PHN.
Acyclovir, valacyclovir, and famciclovir are indicated for the immunocompetent patient older than 50 years with herpes zoster and should be started within 48 hours of the viral episode to receive the most benefit from therapy. These drugs reduce the duration of viral shedding, limit the duration of new lesion formation, and accelerate healing and pain resolution. They are all safe and well tolerated, but because of superior pharmacokinetic profiles and simpler dosing regimen, the latter two are preferred to acyclovir.
Intravenous acyclovir is the treatment of choice in immunocompromised patients, having been shown to halt disease progression, prevent dissemination and speed recovery in immunocompromised patients.
The U.S. Food and Drug Administration (FDA) has approved a live attenuated vaccine for use in the United States to reduce the risk for herpes zoster in older adults (≥60 years) without compromised immune systems. The vaccine is effective in preventing herpes zoster and decreasing the incidence of complications and is well tolerated.

Question 46

Treatment of pain in herpes zoster

Answer 46

The pain of PHN—described variably as continuous deep aching, burning, sharp, stabbing, and shooting, and triggered by light touch over the affected dermatomes—is often debilitating and difficult to treat. Singly or in combination, tricyclics (amitriptyline or desipramine), selective serotonin reuptake inhibitors (sertraline or nefazodone hydrochloride), anticonvulsants (carbamazepine and gabapentin), oral opioids (oxycodone), and topical capsaicin cream or lidocaine patches are helpful for about 50% of patients. Intravenous acyclovir followed by oral valacyclovir was found to reduce the pain of PHN in more than 50% of treated patients

Question 47

Clinical features of disorders of the dorsal root ganglia (sensory neuronopathies) when a) large cells and b) small cells are affected

Answer 47

a) Large-cell dropout leads to kinesthetic sensory impairment, poor coordination, loss of manual dexterity, ataxia, and areflexia
b) small-cell depletion contributes to a hyperalgesic state marked by burning pains and painful paresthesias.

The sensory neuronopathies are characterized by asymmetric, nonlength-dependent abnormalities of SNAPs, a global decrease in SNAP amplitudes, and hyperintensities on T2-weighted MR images of the dorsal spinal cord

Question 48

Differential diagnosis of sensory neuronopathy and predominantly sensory polyneuropathy

Answer 48

Favoring the diagnosis of neuronopathy are the following findings:

• the presence of limb ataxia early in the disease
• asymmetrical sensory loss at onset
• upper limb sensory loss
• lost or attenuated upper-limb sensory action potentials
• relatively normal motor conduction studies

Question 49

Paraneoplastic sensory neuronopathy: a) Clinical and paraclinical findings

Answer 49

a) the disorder is developing over weeks to months and is characterized by ataxia and hyperalgesia while muscle strength is well preserved. Some patients have clinical signs of brainstem and cerebral dysfunction, reflecting a more widespread encephalomyelitis. The neuronopathy may antedate the diagnosis of cancer, usually small-cell lung carcinoma, by months to years.

b)
- The CSF profile discloses elevated protein concentration and a mild mononuclear cell pleocytosis. - Nerve conduction studies reveal widespread loss of sensory potentials.
- Neuropathological features include inflammation and phagocytosis of the sensory neurons in the DRG
- it is is associated with the presence of specific antineuronal (anti-Hu) antibodies

Question 50

Causes of DRG neuronopathy

Answer 50

• paraneoplastic
• hereditary
• toxic (pyridoxine abuse, cisplatin etc)
• autoimmune (sjogren etc)

Question 51

For which part of the limb are the motor fibers carried by a) the medial and lateral chord and b) the posterior chord

Answer 51

a) The lateral and medial cords carry motor fibers to the ventral muscles of the limb
b) The posterior cord carries motor fibers to the dorsal muscles of the limb

Question 52

Motor and cutaneus nerves arising from the brachial plexus at the level of the trunks and chords

Answer 52

• Motor
• Branches of the anterior primary rami C5, C6, C7: Long thoracic nerve –> serratus anterior
• Branches of the anterior primary rami C5: dorsal scapular nerve –> levator scapulae and rhomboids from
• Branch of the upper trunk: suprascapular nerve –> supraspinatus and infraspinatus muscles
• Branch of the lateral chord: pectoralis major
• Branch of the medial chord: pectoralis minor
• Branch of the posterior chord: subscapularis, latissimus dorsi, and teres major muscles

*Cutaneus sensory
posterior cord –> posterior cutaneous nerve of the arm
medial cord –> medial cutaneous nerve of the arm and medial cutaneous nerve of the forearm

Question 53

Clinical features of upper trunk lesions

Answer 53

Weakness and sensory loss in a C5–C6 distribution.
Affected muscles include the supraspinatus and infraspinatus, deltoid, biceps, brachialis, and brachioradialis, so the patient is unable to abduct the arm at the shoulder or flex at the elbow. If a lesion is so proximal that it involves the C5 ramus, the rhomboids and levator scapulae are also affected. The arm hangs at the side internally rotated at the shoulder, with the elbow extended and the forearm pronated in a “waiter’s tip” posture.
The biceps and brachioradialis reflexes are diminished or absent
Sensory loss is found over the lateral aspect of the arm, forearm, and thumb

Question 54

Clinical features of lower trunk lesions

Answer 54

Weakness, sensory loss, and reflex changes in a C8–T1 distribution.
Weakness is present in both median- and ulnar supplied intrinsic hand muscles and in the medial finger and wrist flexors.
The finger flexion reflex is diminished or absent
Sensory loss over the medial two fingers, the medial aspect of the hand, and the forearm

Question 55

Clinical features of posterior chord lesions

Answer 55

A posterior cord lesion produces weakness in the territory of muscles innervated by both radial and axillary nerves.
Sensory loss occurs in the distributions of the posterior cutaneous nerve of the forearm and the radial and axillary nerves. This results in sensory loss over the posterior aspect of the arm, the dorsal surface of the lateral aspect of the hand, and a patch of skin over the lateral aspect of the arm.

Question 56

Clinical features of lateral chord lesions

Answer 56

Weakness in muscles supplied by the musculocutaneous nerve, as well as weakness in the muscles of the median nerve supplied by the C6 and C7 roots (the pronator teres and flexor carpi radialis muscles). The median and ulnar nerve fibers originating from C8 and T1 segments are spared, and thus there is no intrinsic hand muscle weakness

Question 57

Clinical features of median chord lesions

Answer 57

In medial cord lesions, there is weakness in all ulnar nerve– supplied muscles and in the C8 and T1 median nerve– supplied muscles

Question 58

Spectrum of severity of axon-loss in brachial plexus neuropathies determined by the results of the electrodiagnostic study

Answer 58

In the context of a minimal lesion affecting both sensory and motor fibers, SNAPs and CMAPs will typically be unaffected, but needle examination will disclose fibrillation potentials because the loss of one motor fiber will result in denervation of hundreds of muscle fibers.
With an increase in lesion severity, SNAPs become attenuated while CMAPs are still spared.
The most severe lesions compromise sensory and motor responses

Question 59

When do preganglionic and postganglionic lesions coexist and electrodiagnostic findings

Answer 59

a) this situation is encountered most commonly in patients with trauma that damages both the plexus and avulses nerve roots. It is also found in some peripheral radiculoplexus neuropathies such as diabetes and in malignant plexopathies in which tumor not only injures the plexus but also infiltrates the nerve roots by tracking through the intervertebral foramina
b) electrodiagnostic studies disclose paraspinal muscle fibrillation and absent SNAPs

Question 60

Neurogenic thoracic outlet syndrome: clinical features

Answer 60

The clinical and electrophysiological findings point to a lesion of the lower trunk of the brachial plexus.
Pain is usually the first symptom, with either aching noted on the inner side of the arm or soreness felt diffusely throughout the limb. Tingling sensations accompany pain and are felt along the inner side of the forearm and in the hand. Most patients note slowly progressive wasting and weakness of the hand muscles.
The physical examination discloses hand muscle weakness and atrophy, most marked in the lateral part of the thenar eminence. In a smaller number of patients, there is mild atrophy and weakness in the forearm muscles. Sensory loss is present along the inner side of the forearm. Except for the occasional Raynaud-type episode, vascular symptoms and signs are uncommon

Question 61

Neurogenic thoracic outlet syndrome: electrodiagnostic tests

Answer 61

Electrodiagnostic studies on the affected side disclose a reduced median motor response with normal median sensory amplitudes, along with a mildly reduced ulnar motor response and reduced ulnar sensory amplitude. The needle electrode examination typically discloses features of chronic axon loss with mild fibrillation potential activity in C8- and T1-innervated muscles

Question 62

Pancoast syndrome: a) etiology and b) clinical features

Answer 62

a) a superior pulmonary sulcus tumor, the vast majority of which are nonsmall-cell bronchogenic carcinomas. The tumor arises near the pleural surface of the apex of the lung and grows into the paravertebral space and posterior chest wall, invading the C8 and T1 extraspinal nerves, the sympathetic chain and stellate ganglion, the necks of the first three ribs, and the transverse processes and borders of the vertebral bodies of C7 through T3. The tumor may eventually invade the spinal canal and compress the spinal cord
b) Presenting signs and symptoms include: severe shoulder pain radiating to the head and neck, axilla, chest, and arm; pain and paresthesias of the medial aspect of the arm and the fourth and fifth digits; and weakness with atrophy of intrinsic hand muscles

Question 63

Differential diagnosis of metastatic brahial plexopathy and radiation induced plexopathy

Answer 63

A painful lower-trunk lesion with Horner syndrome strongly suggests metastatic plexopathy, whereas a relatively painless upper-trunk lesion with lymphedema favors radiation-induced plexopathy In patients with metastatic disease,
MRI may identify a mass adjacent to the brachial plexus and reveal whether the tumor has encroached on the epidural space.
Magnetic resonance neurography is a novel noninvasive means of helping to exclude radiation-induced tumor in patients presenting with brachial plexopathy who have undergone prior radiation therapy to the brachial plexus
Needle EMG is helpful in separating radiation-induced plexopathy from neoplastic plexopathy by the presence of myokymic discharges in the former

Question 64

Radiation induced plexopathy: clinical features

Answer 64

Limb paresthesias and swelling are common complaints. Although the pain of radiation plexopathy is usually less intense than that of metastatic plexopathy, it may nonetheless be problematic (severe and persistent), requiring opioids and chemical sympathectomy.
Weakness is usually most prominent in muscles innervated by branches of the upper trunk, but involvement of the entire limb from damage to the upper and lower portions of the plexus has also been described.

Question 65

Radiation induced plexopathy: electrodiagnostic studies

Answer 65

In the early and middle stages of radiation plexopathy, nerve conduction studies disclose features of demyelinating conduction block, but as time passes, there is conversion to axon loss.
Needle EMG is helpful in separating radiation-induced plexopathy from neoplastic plexopathy by the presence of myokymic discharges in the former. These are spontaneously occurring grouped action potentials (triplets or multiplets) followed by a period of silence, with subsequent repetition of a grouped discharge of identical potentials in a semi-rhythmic manner. They appear to result from spontaneous activity in single axons induced by local membrane abnormalities. They have not been reported in cases of tumor plexopathy.

Question 66

Idiopathic brachial plexopathy (neuralgic amyotrophy): motor symptoms

Answer 66

Weakness of the upper extremity likely evolves during the period of intense pain, but may not be immediately appreciated by the patient, who is reluctant to move the limb and further exacerbate their pain. This often results in the classic description of weakness that is coincident with a lessening or resolution of the patient’s pain. The pattern of weakness seen is highly variable. Patchy weakness is common, with sparing of one or more muscles in the same root, trunk, or cord distribution. Similarly, there is increasing recognition that this illness need not always be associated with circumscribed lesions of trunks or cords, but may present as discrete lesions of individual peripheral nerves, including the suprascapular, axillary, musculocutaneous, long thoracic, median, anterior interosseous and posterior interosseosus nerves. A minority of patients may have involvement of nerves outside the brachial plexus proper including the phrenic nerves, cranial nerves VII and X, and the lumbosacral plexus.
In a small number of patients, unilateral or bilateral diaphragmatic paralysis occurs with no abnormalities on clinical or electrodiagnostic examinations of the limbs. In such cases, the combination of acute shoulder pain with respiratory symptoms should suggest the diagnosis. . One-third of cases are bilateral, but many fewer are symmetrical. Rarely, symptoms may recur episodically for a year or more

Question 67

Idiopathic brachial plexopathy (neuralgic amyotrophy): sensory symptoms

Answer 67

Patients often describe abrupt onset of a sharp, stabbing, throbbing, or aching pain involving the shoulder, scapular area, trapezius ridge, or upper arm, forearm or hand. Within hours, this pain will have escalated to a peak severity that is often beyond anything the patient will have previously experienced, and then will persist for up to 4 weeks on average before gradually resolving (though rapid resolution of pain within 24 hours and intractable pain lasting months may be seen in 5% and 10% of cases, respectively). During this period, the patient may hold their arm in a characteristic posture, flexed at the elbow and adducted against the body, in an effort to minimize traction on the plexus, which may exacerbate pain symptoms.
Sensory loss, found in two-thirds of patients and most commonly over the outer surface of the upper arm and the radial surface of the forearm, is usually less marked than the motor deficit, although the spectrum of brachial plexus neuropathy includes patients with isolated clinical and electrophysiological sensory deficits

Question 68

Idiopathic brachial plexopathy (neuralgic amyotrophy): electrodiagnostic studies

Answer 68

Electrodiagnostic testing is helpful in confirming the diagnosis and ruling out other conditions.
Findings suggest axonal lesions of peripheral nerves occurring singly (mononeuritis) or in various combinations (mononeuritis multiplex).
Sensory studies are abnormal in up to one-third of patients; the most common abnormality is reduced amplitude of one or more sensory action potentials of the median, ulnar, and radial nerves and the lateral and medial antebrachial cutaneous nerves.
Needle EMG is helpful because it shows absence of fibrillation potentials in the cervical paraspinal muscles, thereby pointing to a pathological process distal to the DRG. Needle EMG is also helpful in sorting out the problems of localization, identifying lesions localized to the brachial plexus, individual peripheral nerves, or peripheral nerve branches. Finally, in a small number of patients, needle EMG is abnormal on the asymptomatic side as well as the symptomatic side, indicating that brachial plexus neuropathy can sometimes be subclinical.

Question 69

Idiopathic brachial plexopathy (neuralgic amyotrophy): imaging

Answer 69

The MRI appearance in idiopathic brachial plexopathy reveals findings of diffuse high T2 signal intensity abnormalities and fatty atrophy of involved muscles

Question 70

Idiopathic brachial plexopathy (neuralgic amyotrophy): treatment

Answer 70

In the acute stage of the disorder, long-acting nonsteroidal anti-inflammatory drugs (NSAIDs) and opioid analgesics are required to control pain.
Evidence from one open-label retrospective series suggests that oral prednisone given in the first month after the onset can shorten the duration of the initial pain and leads to earlier recovery in some patients.
Arm and neck movements often aggravate pain, so immobilization of the arm in a sling is helpful. With the onset of paralysis, range-ofmotion exercises help prevent contractures.
Following the phase of acute pain, there are two additional categories of pain.
The first, experienced by nearly 80% of patients, is a shooting or radiating neuropathic pain, believed to originate from the heightened mechanical sensitivity of damaged nerves of the plexus and lasting for weeks to months. This pain may respond to gabapentin and tricyclic medications.
A second type of pain that develops in many is a musculoskeletal-type pain localized to the origin or insertion of the paretic or compensating muscles, especially in the periscapular, cervical, and occipital regions. This pain requires physical therapy modalities.

Question 71

Formation of lumbar plexus and major branches

Answer 71

The lumbar plexus is formed within the psoas major muscle by the anterior primary rami of lumbar spinal nerves L1, L2, L3, and L4. It is connected to the sacral plexus in the true pelvis by the anterior division of L4

Branches of the lumbar plexus include:

1) the iliohypogastric and ilioinguinal nerves arising from L1 (with a contribution from T12)
2) the lateral femoral cutaneous nerve of the thigh originating from the posterior divisions of L2 and L3
3) the genitofemoral nerve arising from the anterior division of L1 and L2
4) the femoral nerve, formed from the posterior divisions of L2, L3, and L4
5) the obturator nerve, formed by the anterior divisions of L2, L3, and L4

Question 72

Formation of sacral plexus and major branches

Answer 72

The sacral plexus derives from the anterior rami of spinal nerves L4, L5, S1, S2, and S3

Like the lumbar plexus, the sacral plexus has anterior and posterior divisions. The anterior division contributes to the tibial portion, and the posterior division contributes to the peroneal portion of the sciatic nerve

Branches of the sacral plexus include:

1) the superior and inferior gluteal nerves arise from posterior divisions of the sacral plexus and supply the gluteus medius and minimus muscles and the gluteus maximus, respectively
2) The posterior cutaneous nerve of the thigh is formed by the anterior divisions of S1, S2, and S3
3) The pudendal nerve originates from the undivided anterior primary rami of spinal nerves S2, S3, and S4 and extends into the gluteal region

Question 73

Characteristic findings in lumbar plexopathy

Answer 73

• Weakness and sensory loss in both obturator- and femoral innervated territories
• Weakness of hip flexion, knee extension, and hip adduction
• Sensory loss over the anteromedial aspect of the thigh - The knee jerk is absent or depressed

Question 74

Characteristic findings in sacral plexopathy

Answer 74

• Findings in sacral plexopathy include weakness and sensory loss in the territories of the gluteal (motor only), peroneal, and tibial nerves.
• Leg weakness is typically extensive and involves the hip extensors and abductors, knee flexors, and ankle plantar flexors and dorsiflexors
• Sensory loss is found over the posterior aspect of the thigh, the anterolateral and posterior aspects of the leg below the knee, and the dorsolateral and plantar surfaces of the foot.
• Vasomotor and trophic changes may also be found in these areas.
• The ankle jerk is reduced or absent

Question 75

Contribution of electrodiagnostic studies in disorders of the lumbosacral plexus

Answer 75

1) the EMG is helpful in identifying a motor-sensory syndrome as a plexopathy and not a radiculopathy.
The diagnosis of plexopathy is confirmed if the EMG discloses denervation (fibrillation potentials and positive sharp waves) and reduced recruitment (reduced numbers of motor units, firing rapidly) in muscles innervated by at least two lumbosacral segmental levels and involving at least two different peripheral nerves. An isolated plexopathy should not be associated with EMG abnormalities in paraspinal muscles. *

2) EMG findings help determine whether a lumbosacral plexopathy is associated with a polyneuropathy.
In the presence of the latter, signs of denervation and reinnervation are found bilaterally, especially in the distal muscles.

3) EMG findings may strongly suggest a particular type of plexopathy; for example, myokymic discharges point to the diagnosis of radiation plexopathy
4) Reduced SNAP amplitude (sural and superficial peroneal) indicates loss of axons distal to the DRG of S1 and L5, respectively.
5) Prolongation in F-wave latency with normal motor nerve conduction studies distally suggests a proximal lesion, either at a root or plexus level.
* however, a number of pathological processes including diabetes, radiation-induced changes, inflammation, vasculitis, and neoplasia may all involve the roots in addition to the plexus and produce a radiculoplexopathy

Question 76

Differential diagnosis of lumbosacral plexopathy

Answer 76

The differential diagnosis of lumbosacral plexopathy includes:

1) spinal root disorders (e.g., lumbosacral radiculopathy, polyradiculoneuropathy, cauda equina syndrome, anterior horn cell disorders)
2) myopathic conditions.

Question 77

Two major anatomical syndromes are associated with iliopsoas hematoma

Answer 77

1) In the first, the femoral nerve is the sole
affected portion of the lumbar plexus. The hematoma arises in the iliacus and causes distention of the dense overlying fascia above the inguinal ligament.
2) In the second syndrome, hemorrhage arises in the psoas muscle or begins in the iliacus muscle and extends into the psoas. In this case, other components of the plexus, the obturator and lateral femoral cutaneous nerves, are involved.

Question 78

Causes of Structural Lumbosacral Plexopathy

Answer 78

Hemtaoma
Abscess
Aneurysm
Neoplasia
Pregnancy
Trauma

Question 79

Causes of Nonstructural Lumbosacral Plexopathy

Answer 79

Idiopathic
Radiation
Vasculitis