What makes up the neuromuscular system?
- Nerves (LMNs)
- Neuromuscular junction
- Skeletal muscle
What are the types/locations of neuromuscular disease?
- Neuropathy
- Junctionopathy
- Myopathy
When defining the problem, what two cardinal signs help you suspect neuromuscular disease?
- Weakness WITHOUT ataxia
i. Short strides
ii. Stilted gait
iii. Not ataxic - Exercise intolerance
What history and physical exam findings may make you suspicious of neuromuscular disease?
Hx: Dysphagia Dysphonia Regurg Dyspnoea Gait abnormality
PE:
Muscle atrophy
Muscle hypertrophy
Myalgia
When you have weakness, what system could be involved?
- CVRS
- Systemic/metabolic
- Neurological
When working up a weakness case how can you rule out CVRS dz?
History of cough/CHF PE: Murmur, arrhythmia, hypotension, pulses Diagnostic test: NIBP Thoracic xray Echocardiography Cardiac toponin I
When working up a weakness case how can you rule out systemic/metabolic dz?
Pale MM, pyrexia, distended abdomen
Diagnostics:
Haem and biochem
If you have a cat with severe cervical ventroflexion, what electrolyte could be involved?
Myopathy related to hypokalaemia
If you have a dog that is very weak with marked fine tremors, what electrolyte could be involved?
Hypocalcaemia
How can you define the system in neurological cases?
- Is the patient neurologically normal or abnormal
2. Where is the lesion
What does a palmigrade/plantigrade posture suggest?
Seen in cats with neuropathies
Are the postural reactions usually normal or abnormal in a neuromuscular diseased animal?
May be normal - support their weight
Some so weak they cannot show proprioception
When are spinal reflexes reduced?
Neuropathy
What is marked muscle atrophy suggestive of?
Neuropathy (denervation atrophy).
Much more marked than disuse atrophy
What are the possible locations for neuromuscular disease?
Generalised
Focal (Cranial nerves)
Focal (Spinal nerves)
What would help you define the location to a neuropathy?
Reduced to absent spinal reflexes
Plantigrade/palmigrade stance
Reduced to absent muscle tone
+/- Neurogenic muscle atrophy
What would help you define the location to a junctionopathy?
Normal to reduced spinal reflexes
Exercise intolerance
What would help you define the location to a myopathy?
Often normal spinal reflexes
Exercise intolerance
+/- myalgia, muscle atrophy/hypertrophy
Is it always possible to localised to neuropathy/junctionopathy/myopathy?
Often not possible to go further than localising to neuromuscular
Most marked and severe signs tend to be neuropathies
What diagnostic tests can you perform to localise neuropathy/junctionopathy/myopathy?
Muscle enzymes (myopathy) Increased CK Increased AST Increased ALT Urinalysis (myopathy) Myoglobinuria (dark brown urine) Electrodiagnostics
What is electromyography?
Cannot determine aetiology
Needle into muscle and detect spontaneous electrical activity
Spontaneous activity = muscle pathology/denervated
Silent = normal muscle/disuse atrophy
Neuropathy or myopathy (rules out junctionopathy and metabolic cause)
What are nerve conduction studies?
Look further at nerve itself - stimulation
Differentiate neuropathy and myopathy
Neuropathy = decreased amplitude/slowed conduction velocity
Myopathy = normal
How can neuromuscular ddx be grouped?
- Generalised acute
- Generalised chronic
- Focal acute
- Focal chronic
Give some examples of generalised acute neuromuscular differentials…
Acute canine polyradiculoneuritis Acquired myasthenia gravis Botulism Hypocalcaemic Hypokalaemia
Give some examples of generalised chronic neuromuscular differentials…
Inherited/breed specific polyneuropathy
Diabetic polyneuropathy
Myasthenia gravis
Hypokalaemia
Give some examples of acute focal neuromuscular differentials….
Trigeminal neuropathy Facial neuropathy Brachial plexus avulsion Myasthenia gravis Masticatory myositis
Give some examples of chronic focal neuromuscular differentials…
Degenerative lumbosacral stenosis
Peripheral nerve sheath tumour
Myasthenia gravis
Masticatory myositis
What further diagnostic tests can be done in a neuromuscular disease case?
- All neuromuscular cases: Haem Biochem Urinalysis - Suspicion of endocrine: ACTH stim T4/TSH - Suspicion of systemic dx: Thoracic/abdominal imaging - Serology - Advanced imagine - CSF analysis - Last resort = nerve and muscle biopsies
What do 80% dogs with acquired myasthenia gravis have?
Megaoesophagus and aspiration pneumonia
What serology can you perform in a neuromuscular case?
- Acquired myasthenia gravis: Nicotinic ACh receptor antibody titre - Masticatory myositis: Type 2M muscle fibre antibody titre - Infectious agents: Toxo/neospora FeLV/FIV
General considerations for tx of neuromuscular disease…
- Recumbent patients require supportive care, fliuds, nutrition, bladder managemet
- Severe weakness may lead to resp muscle weakness - ventilate
- PHYSIO and HYDROTHERAPY essential to maintain muscle mass
What is dysphonia?
A change in vocalisation
Why does neuromuscular disease present as weakness without ataxia?
Spinal cord and brain not affected
Why might patients with a junctionopathy appear normal prior to exercise?
Junctionopathies tend not to cease all transmission, the neuromuscular junction simply becomes less efficient
What is the role of edrophonium?
Anticholinesterase (increases acetylcholine in neuromuscular junction)
Describe the edrophonium response test
Intravenous bolus of edrophonium will allow animals with myasthenia gravis to be able to walk for longer