A 6-year-old girl from rural Maharashtra presents with a 3-month history of low-grade fever, weight loss, and persistent cough. Her mother reports that the child's uncle, who lives in the same household, was diagnosed with pulmonary tuberculosis 4 months ago and is now on anti-TB therapy. On examination, the child appears malnourished. Chest X-ray shows a right hilar lymphadenopathy with no parenchymal consolidation. Mantoux test (5 TU) shows an induration of 12 mm. Sputum smear microscopy is negative. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Primary Tuberculosis with Hilar Lymphadenopathy ### Key Distinguishing Features **Key Point:** Primary TB in children typically presents with hilar lymphadenopathy and minimal or absent parenchymal involvement, unlike adult-type cavitary disease. ### Pathophysiology In primary TB (most common in children <5 years but seen up to age 8–10): 1. Initial infection occurs at the lung periphery (Ghon focus) 2. Regional lymph node enlargement follows (hilar/mediastinal) 3. The triad = Ghon focus + lymphangitis + regional lymphadenopathy 4. Sputum remains negative because there is no cavitation or bronchial communication ### Clinical & Radiological Features of Primary TB | Feature | Primary TB | Adult-Type TB | |---------|-----------|---------------| | **Age** | <8–10 years | Adolescents/adults | | **CXR findings** | Hilar lymphadenopathy ± atelectasis | Cavitary lesions, upper lobe infiltrates | | **Sputum smear** | Negative (closed lesion) | Often positive | | **Mantoux** | Usually positive (>5 mm) | Usually positive | | **Progression** | Risk of dissemination, miliary TB | Progressive cavitary disease | ### Why This Patient Has Primary TB - **Age 6 years** → primary TB age group - **Hilar lymphadenopathy only** → classic primary TB CXR pattern - **Negative sputum smear** → no cavitation or bronchial involvement - **Positive Mantoux (12 mm)** → TB infection confirmed - **Recent household exposure** → source case identified - **No parenchymal consolidation** → rules out adult-type TB **High-Yield:** In children, TB is primarily a **lymph node disease**, not a lung parenchymal disease. Hilar/mediastinal lymphadenopathy is the hallmark of primary TB. **Clinical Pearl:** A child with TB exposure, constitutional symptoms, and hilar lymphadenopathy on CXR should be treated as TB even with negative sputum smear — sputum negativity is expected in primary TB. ### Management Implications - Start anti-TB therapy (4-drug regimen: HRZE for 2 months, then HR for 4 months) - Nutritional support and vitamin B6 supplementation - Monitor for complications (mediastinal lymph node compression, bronchial obstruction) [cite:Park 26e Ch 9]