Question
A 45 year old smoker comes to medicine OPD with a history of low grade fever with an evening rise of temperature, loss of weight and productive cough for the past two months. Recently, he had hemoptysis. Microscopic examination of sputum sample revealed acid fast bacilli.
- (a) What is the most probable clinical diagnosis 1 mark(s)
- (b) Name the etiological agent 1 mark(s)
- (c) Describe the pathogenesis of this disease 3 mark(s)
- (d) Describe the laboratory diagnosis in detail e) Discuss the drug resistance that can occur in this etiological agent f) Name the national health programme for this disease 5 mark(s)
Answer
(a) Most probable clinical diagnosis: Pulmonary tuberculosis — chronic low-grade fever with evening rise, weight loss, productive cough of two months’ duration, haemoptysis, and acid-fast bacilli on sputum microscopy.
(b) Etiological agent: Mycobacterium tuberculosis.
(c) Pathogenesis: inhaled droplet nuclei reach the alveoli, where bacilli are phagocytosed by alveolar macrophages, surviving and multiplying intracellularly to form the initial Ghon focus; spread via lymphatics to hilar lymph nodes constitutes the primary complex. Cell-mediated immunity (Th1 response, granuloma formation with central caseous necrosis) typically contains the infection into a latent state. Reactivation (post-primary TB), favoured by waning immunity/smoking (as in this patient), typically occurs in the apical/posterior upper lobes (higher oxygen tension), causing progressive cavitary disease, tissue destruction, and erosion into blood vessels producing haemoptysis.
(d) Laboratory diagnosis:
- Sputum smear microscopy — Ziehl-Neelsen stain, demonstrating acid-fast bacilli; rapid, low-cost, though limited sensitivity.
- CBNAAT/GeneXpert MTB/RIF — rapid molecular test, detecting M. tuberculosis DNA and rifampicin resistance simultaneously; the preferred initial test under India’s NTEP.
- Culture — Lowenstein-Jensen medium (solid, 2–8 weeks) or liquid culture systems (e.g., BACTEC MGIT, 1–3 weeks); the gold standard, also allowing full phenotypic drug-susceptibility testing.
- Line Probe Assay (LPA) — detailed first- and second-line drug-resistance profiling.
- Chest X-ray — supportive (cavitation, upper-lobe infiltrates), not diagnostic alone.
(e) Drug resistance: Multi-Drug Resistant TB (MDR-TB) — resistance to at least isoniazid and rifampicin, arising from spontaneous chromosomal mutations selected under inadequate treatment; Extensively Drug-Resistant TB (XDR-TB) — MDR-TB with additional resistance to fluoroquinolones and second-line injectable/newer agents. Managed with longer, individualized regimens using second-line drugs (bedaquiline, linezolid, fluoroquinolones, clofazimine), guided by drug-susceptibility testing.
(f) National health programme: the National Tuberculosis Elimination Programme (NTEP) (formerly RNTCP), providing free diagnosis and DOTS (Directly Observed Treatment, Short-course) therapy, with a target of TB elimination in India by 2025.