Miliary tuberculosis — DTM&H MCQ

Correct answer: A — Miliary tuberculosis

The correct answer is A, Miliary tuberculosis. In a person with HIV presenting with fever, weight loss and diffuse tiny (millet seed) pulmonary nodules on chest radiograph, disseminated haematogenous spread of Mycobacterium tuberculosis is the classic and by far most likely cause, especially in a high TB burden setting such as Malawi. HIV-associated immunosuppression predisposes to disseminated rather than localised cavitary disease, and sputum smear is frequently negative in miliary TB because the disease is paucibacillary and disseminated rather than confined to airways with high bacillary load. NICE guidance recommends that rapid nucleic acid amplification testing and mycobacterial culture be used to confirm diagnosis when smear microscopy is negative, since a negative smear does not exclude active tuberculosis, particularly in HIV-positive patients. Why the other options are wrong: E. Melioidosis: caused by Burkholderia pseudomallei, endemic to Southeast Asia and northern Australia, not typically encountered in Malawi, and it more often causes pneumonia with cavitation or abscesses rather than the classic diffuse miliary micronodular pattern. B. Sarcoidosis: causes granulomatous lung disease with hilar lymphadenopathy and reticulonodular change, but it is not linked to HIV, does not present acutely with fever and weight loss in this way, and is far less prevalent than TB in this demographic. C. Pneumocystis pneumonia: typically causes bilateral diffuse ground-glass interstitial infiltrates in advanced HIV (low CD4), not discrete tiny miliary nodules, and is not associated with the weight loss pattern described. D. Histoplasmosis: endemic in the Americas and parts of Africa but far less common than TB as a cause of this presentation in Malawi, and disseminated histoplasmosis, while it can mimic miliary TB, is a much rarer diagnosis in this epidemiological context. Key point: In an HIV-positive patient from a high TB burden region with fever, weight loss and diffuse miliary nodules, smear-negative sputum should never exclude miliary tuberculosis, which remains the leading diagnosis pending nucleic acid amplification testing and culture.

Reference: NICE guideline NG33, Tuberculosis: prevention, diagnosis, management and service organisation (2016, updated), recommendations on microbiology investigations and rapid diagnostic testing in smear-negative and HIV-associated disease, https://www.nice.org.uk/guidance/ng33/chapter/recommendations