## Clinical Diagnosis: Pulmonary TB with Negative Sputum Smear ### Key Features Supporting the Diagnosis **High-Yield:** In children, pulmonary TB commonly presents with negative sputum smear microscopy because: 1. Children have lower bacillary load in respiratory secretions (paucibacillary disease) 2. Difficulty in producing adequate sputum samples 3. Endobronchial TB is more common than cavitary disease in pediatric cases **Clinical Pearl:** The combination of: - Epidemiological link (recent TB exposure in household) - Constitutional symptoms (fever, weight loss, cough for 3 months) - Positive Mantoux test (≥15 mm in vaccinated child is significant; ≥10 mm in unvaccinated is diagnostic) - Radiological findings (hilar lymphadenopathy with parenchymal opacity) - Negative sputum smear (typical in pediatric TB) ...strongly suggests **pulmonary TB in a child**. ### Diagnostic Criteria for Childhood TB | Feature | Pediatric TB | Adult TB | |---------|--------------|----------| | Sputum smear positivity | <10% of cases | 40–60% of cases | | Cavitary disease | Rare (<5%) | Common (30–40%) | | Hilar lymphadenopathy | Prominent | May be absent | | Bacillary load | Low (paucibacillary) | High (multibacillary) | | Culture sensitivity | Gold standard but slow | Gold standard | **Key Point:** In pediatric TB, diagnosis is often clinical and radiological rather than bacteriological. Negative sputum does NOT exclude TB in a child. ### Why This Is Pulmonary TB (Not TB Lymphadenitis) Although hilar lymphadenopathy is present, the parenchymal opacity and cough indicate **parenchymal involvement**, making this pulmonary TB rather than isolated lymphadenitis. [cite:Park 26e Ch 8]
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