As part of my respiratory firm, I’ve sat in on the TB clinic a few times. Yep, a whole clinic just for TB. Most of the time it’s patients that have some respiratory symptoms, mainly cough and haemoptysis and weight loss. Bonus points if they have been abroad recently. Africa or Asia is a Trump card.
The most beneficial thing I’ve learnt from clinic is the names of the four antibiotics used to treat TB. No looking at anything now- Rifampicin, Isoniazid, Ethambutol and Pyramidizine. Well, all but the last one then. That’s, correction- Pyrazinamide. Unfortunately, I remember that one in my head as the one that sounds like ‘Pyramid’ so it always becomes pyramidizine.
Definition: TB is an infectious disease caused by the bacillus Mycobacterium tuberculosis, which typically affects the lungs (pulmonary TB) but can also affect other sites (extrapulmonary TB).
Aetiology/ risk factors:
TB is spread when individuals with pulmonary TB expel bacteria into the air, for example by coughing.
Risk factors: poverty, alcohol, smoking, contact with TB, immunosuppression (e.g. HIV, diabetes, malignancy, extremes of age) and renal disease.
–1.8 million people worldwide died from TB in 2015, including 0.4 million HIV positive individuals. (WHO)
-60% of cases occurred in 6 countries: China, India, Indonesia, Nigeria, Pakistan, South Africa
-In the UK incidence is highest in Asian and West Indian immigrants, children of these immigrants, the homeless and those with HIV infection.
-may be silent
-cough, sputum, haemoptysis
-pleurisy (inflammation of the pleura associated with sharp chest pain upon deep inspiration)
-malaise, weight loss, night sweats, fever
-Erythema nodosum (occasional)
-Pleural effusion or superimposed pulmonary infection (e.g. signs of effusion or consolidation on respiratory exam)
–Mantoux test- test for TB exposure (latent or active TB)
-intradermal injection of Purified protein derivative (PPD) tuberculin (mixture of antigens from Mycobacteria)
-if the patient been exposed to TB they will have a Delayed Type Hypersensitivity immune response, producing an induration.
-48-72 hrs later, measure the size of the induration (palpable raised, hardened area)
-large induration size = positive test (5, 10 or 15 mm, depending on their medical risk factors)
-positive test indicates immunity or previous exposure or BCG
–strong positive test probably means active TB
-not the most reliable test in the world- lots of false positives, and false negatives occur in immunosuppression (lymphoma, AIDs, sarcoid)
–Interferon gamma assay (Elispot)- consider if Mantoux test is positive or non-reliable.
-measures the delayed type hypersensitivity reaction developed after contact with M.tuberculosis. Uses more specific antigens for M.tuberculosis (Mantoux uses mix from Mycobacteria). Better than Mantoux.
-positive result suggests prior exposure to TB. But this can mean quite a few things, so has to be taken in context of the patient presentation. You will get a positive test in a patient with active TB or latent TB or previous latent or active TB that has been fully treated.
–Sputum samples (≥3)- if active TB suggested; send for microscopy, culture and sensitivities (MC&S) of AFB (acid-fast bacilli- Ziehl-Neelsen staining). Bronchoscopy or lavage may be needed if sputum cannot be produced.
–CXR- consolidation, cavitation, fibrosis, calcification- usually in upper lung
-may see hilar or mediastinal lymphadenopathy
Pleural calcification in TB (see the really white lung edge)
–PCR- allows rapid identification of rifampicin (and likely multidrug) resistance
⇒Standard treatment for TB is antibiotics for 6 months:
-2 months: Rifampicin, Isoniazid, Pyrazinamide, Ethambutol
-4 months: Rifampicin, Isoniazid
Other types of TB:
-Miliary TB: widespread dissemination via haematogenous spread (CXR- miliary pattern = nodular opacities through out lung, dot-like)
-Genitourinary TB (including renal TB, endometrial TB)
-Skin TB (lupus vulgaris): jelly-like nodules
-Acute TB pericarditis, chronic pericardial effusion and constrictive pericarditis
Take home message: TB can mess up just about any organ
References: Cheese & Onion, WHO Global TB report 2016, Kuman & Clark's