Tuberculosis

Question 1

What is TB?

Answer 1

Granulomatous disease caused by Mycobacterium tuberculosis

Question 2

What are the types of TB? (x3)

Answer 2

• PRIMARY: initial infection may be pulmonary (from inhalation of cough of infected person) or occasionally GI
• MILIARY: characterised by tiny lung lesions and haematogenous dissemination (leading to extra-pulmonary signs and symptoms)
• POST-PRIMARY: caused by reinfection or reactivation

Question 3

What is the aetiology of TB?

Answer 3

M. tuberculosis is an acid-fast bacillus which survives after phagocytosis by macrophages

Question 4

What is the epidemiology of TB?

Answer 4

Asian immigrants 30 times more prevalent than native white UK population

Question 5

What are the pulmonary signs and symptoms of TB? Disease course?

Answer 5

• COURSE: becomes dormant before it progresses to active TB
• Cough
• Haemoptysis in 10%, more common in post-primary
• Pleural effusion and pleuritic chest pain from pleural TB (entering pleural space)
• Fibrosis
• FLAWS

Question 6

What are the extra-pulmonary signs and symptoms of TB? (x8)

Answer 6

• LYMPHATIC TB: suppuration cervical lymphadenopathy, leading to abscesses and spread to skin (scrofuloderma)
• SKELETAL TB: commonly vertebrae (leading to Pott’s disease), hips and knee, manifesting as pain, spinal cord compression from abscesses
• CNS TB: meningitis and tuberculomas
• PERITONEAL TB: ascites and peritonitis; enteritis most commonly localised in RLQ
• GENITOURINARY TB: dysuria, haematuria, increased frequency
• PERICARDIAL FLUID: leading to tamponade or pericardial fibrosis (constrictive pericarditis)
• SKIN: Lupus vulgaris (jelly-like red-brown glistening plaques), Erythema nodosum
• Phlyctenular conjunctivitis: small, yellow-grey raised lumps on cornea and conjunctiva due to immune reaction

Question 7

What does lupus vulgaris look like?

Answer 7

Jelly-like red-brown glistening plaques on face

Question 8

What are the immediate investigations for TB? (x2)

Answer 8

• ISOLATE PATIENT and obtain CXR
• THREE SPUTUM SAMPLES for (1) acid-fast bacilli smear, (2) culture, and (3) nucleic acid amplification test

Question 9

What skin tests are there for TB? (x3)

Answer 9

• TUBERCULIN TEST: which is positive if previous exposure to TB, and may also indicate infection
• MANTOUX TEST: intradermal PPD injection (inactive TB protein derivative) leading to induration and erythema after 72 hours
• HEAF TEST: drop of PPD on forearm and fire spring-loaded needled gun. Read after 3-7 days and graded according to papule size and vesiculation

Question 10

What other tests are there for TB? (x3)

Answer 10

• IFN-GAMMA: in latent TB, exposure of TB antigens to T cells releases IFN with high specificity, so can be used to diagnose latent TB if tuberculin test is positive
• HIV: coincident disease
• CT, LYMPH NODES, PLEURAL BIOPSY: sample other organs and assess for damage

Question 11

What does TB look like on CXR for each type?

Answer 11

• PRIMARY: peripheral consolidation, hilar lymphadenopathy
• MILIARY: fine shadowing
• POST-PRIMARY: upper lobe shadowing, streaky fibrosis and cavitation, calcification, pleural effusion, hilar lymphadenopathy