Question
A 40-year-old male presented to pulmonary medicine outpatient department with history of productive cough of more than 3 weeks duration, evening rise of temperature and loss of weight. Microscopic examination of sputum showed acid fast bacilli.
- (a) What is the most probable clinical diagnosis 1 mark(s)
- (b) Name the etiological agent 1 mark(s)
- (c) Discuss the pathogenesis of the disease 3 mark(s)
- (d) Describe the lab diagnosis in detail e) Add a note on the drug resistance seen in this organism f) Name the national programme for this disease 5 mark(s)
Answer
(a) Most probable clinical diagnosis: Pulmonary tuberculosis — productive cough >3 weeks, evening rise of temperature, weight loss, and acid-fast bacilli on sputum microscopy is the classical presentation.
(b) Etiological agent: Mycobacterium tuberculosis.
(c) Pathogenesis: inhaled droplet nuclei reach the alveoli, phagocytosed by alveolar macrophages, forming 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 infection into a latent state. Reactivation (post-primary TB), favoured by waning immunity, typically occurs in the apical/posterior upper lobes (higher oxygen tension), causing progressive cavitary disease with chronic symptoms as seen in this patient.
(d) Laboratory diagnosis:
- Sputum smear microscopy — Ziehl-Neelsen stain, demonstrating acid-fast bacilli; rapid, inexpensive, 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 (2–8 weeks) or liquid culture systems (e.g., BACTEC MGIT, 1–3 weeks); the gold standard, also enabling full phenotypic drug-susceptibility testing.
- Line Probe Assay (LPA) — detailed drug-resistance profiling (first- and second-line).
- Chest X-ray — supportive, 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 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.