Tuberculosis Flashcards
What is the causative organism in tuberculosis?
Mycobacterium tuberculosis
What are risk factors for the development of tuberculosis?
- Immunosuppressed
- Malnutrition
- Alcoholism, vagrants, previous gastric surgery
- Malignancy
- Diabetes mellitus
- Adolescence, elderly
- High Risk areas - Recent immigrants from high prevalence countries
What are the general features of mycobacteria?
- Non-motile bacilli
- Very slow growing
- Obligate anaerobes
- Facultative intracellular pathogens - usually mononuclear phagocytes.
- Thick cell walls - lipids, peptidoglycans and arabinomannans.
What is the pathogenesis of primary TB?
Large droplets inhaled and impact on the large airways. Alveolar antigen presenting cells ingest the bacteria and present MHC II. These cells move to local lymph nodes in the mediastinum, where they meet Th1 helper cells.
Mass proliferation of Th1 cells occurs. These migrate back to the alveolus where they activate alveolar macrophages. These release enzymes, oxygen free radicals and other chemicals which cause tissue damage to the alveolus.
If the macrophages don’t kill the mycobacterium, they can sequester them - they elongate and coalesce to form Langerhans giant cells, which form granulomas.
What is the outcome of the immune response in primary TB?
In normal heatlhy individuals, the immune response leads to fibrosis. This subsequently results in complete healing of the caseating areas, with many of the caseated areas becoming calcified.
Some mycobacterium are contained in these calcified areas and are kept at bay by the immune system. These can cause latent infection when the immune system becomes weakened or compromised.
What is a ghon complex?
A lesion seen in tuberculosis consisting of a calcified focus of infection and an associated lymph node
What occurs if primary TB is not controlled?
Active primary TB
What is a Ghon focus?
A primary lesion usually subpleural, often in the mid to lower zones, caused by Mycobacterium bacilli (tuberculosis) developed in the lung of a nonimmune host (usually a child)
What is latent TB?
Most common type of TB - reactivation of TB in the primary lesions. The sequestered organisms overpower the immune system when it becomes weakened/compromised, and proliferate and release into the blood stream and spread round the body.
What are factors which can cause reactivation of TB?
- HIV co-infection
- Immunosuppressant therapy
- Corticosteroids
- Diabetes mellitus
- End-stage chronic kidney disease
- Malnutrition
- Ageing
What are histological features of TB infection?
Caseating granuloma - with epithelioid macrophages and Langhans giant cells along with lymphocytes, plasma cells, fibroblasts with collagen, and characteristic caseous necrosis in the center. The inflammatory response is mediated by a type IV hypersensitivity reaction. This can be utilized as a basis for diagnosis by a TB skin test.
What is miliary TB?
A form of tuberculosis that is characterized by a wide dissemination into the human body and by the tiny size of the lesions (1–5 mm). Its name comes from a distinctive pattern seen on a chest radiograph of many tiny spots distributed throughout the lung fields with the appearance similar to millet seeds—thus the term “miliary” tuberculosis.
What are clinical features of pulmonary TB?
May be silent
- Cough + Sputum +/- haemoptysis
- Malaise
- Weight loss
- Night sweats
- Pleurisy
- Pleural effusion
What are features of genitourinary TB?
- Dysuria
- Loin/back pain
- Frequency
- Haematuria
- Sterile pyuria
What are features of TB meningitis?
- Headache
- Fever
- Vomiting
- Abdo pain
- Drowsiness
- Meningism
- Delerium +/- seizures
- Signs - tremor, papilloedema, cranial nerve palsies
What signs might you see in TB meningitis?
- Tremor
- Papilloedema
- Cranial nerve palsies
What features would suggest TB meningitis?
Meningism and low grade fever with active extrameningeal tuberculosis
What cardiac features can present in TB?
- Acute pericarditis
- Chronic pericardial effusion
- Constrictive pericarditis
What is the theory behind Ziehl-Neelsen Staining?
Procedure involves dropping the cells in suspension onto a slide, then air drying the liquid and heat fixing the cells. The slide is flooded with Carbol Fuchsin, which is then heated to dry and rinsed off in tap water.
The slide is then flooded with a 1% solution of hydrochloric acid in isopropyl alcohol (or methanol) to remove the carbol fuchsin, thus removing the stain from cells that are unprotected by a waxy lipid layer. Thereafter, the cells are stained in methylene blue and viewed on a microscope under oil immersion.
Acid-fast bacilli will be bright red after staining.
What might you see on CXR in someone with TB?
- Consolidation
- Cavitation
- Fibrosis
- Calcification
- Ghon complex
- Miliary TB
What are features of miliary TB on CXR?
Haematogenous dissemination of an uncontrolled tuberculous infection.
- Miliary deposits - 1-3 mm diameter nodules, uniform in size and distribution
What is regarded as a positive skin reaction in tuberculin skin test?
Indicated by a delayed hypersensitivity reaction evident 48–72 hours after the intradermal injection:
- Raised indurated lesion >6 mm diameter in non-vaccinated adults
- A raised indurated lesion >15 mm in BCG-vaccinated adults.
