Unmasking TB immune reconstitution inflammatory syndrome — DTM&H MCQ

Correct answer: C — Unmasking tuberculosis immune reconstitution inflammatory syndrome

The correct answer is C, unmasking tuberculosis immune reconstitution inflammatory syndrome. This man has advanced HIV (CD4 42 cells/microlitre) and developed fever, enlarging cervical lymphadenopathy and a new chest radiograph abnormality only 4 weeks after starting ART, with Xpert MTB/RIF confirming Mycobacterium tuberculosis without rifampicin resistance in the node aspirate. This pattern is classic for unmasking TB-IRIS, in which subclinical TB present but undiagnosed before ART is initiated becomes clinically overt as CD4 recovery drives an exaggerated inflammatory response against mycobacterial antigens, typically within the first 1 to 3 months of ART, especially at very low baseline CD4 counts. The diagnosis is confirmed here because active TB has been microbiologically proven, distinguishing unmasking IRIS from a purely paradoxical worsening of already-treated TB. Why the other options are wrong: A. Disseminated strongyloidiasis: this causes gastrointestinal, pulmonary and cutaneous larva currens features from hyperinfection, not Xpert-positive MTB in a lymph node aspirate. E. Primary Pneumocystis pneumonia: presents with progressive dyspnoea and bilateral interstitial infiltrates, not cervical lymphadenopathy, and would not yield MTB on Xpert. B. Efavirenz hypersensitivity reaction: causes rash, fever and hepatitis typically within the first weeks of exposure, but does not explain a positive Xpert for MTB from a lymph node. D. Visceral leishmaniasis: causes fever, hepatosplenomegaly and pancytopenia; it is not detected by an Xpert MTB assay and does not typically cause cervical lymphadenopathy with lung shadowing. Key point: new, microbiologically confirmed TB emerging within weeks of starting ART in a patient with a very low baseline CD4 count is unmasking TB-IRIS, and the priority is to start TB treatment while continuing ART unless a life-threatening complication mandates specialist reassessment.

Reference: MSF Medical Guidelines / WHO-aligned practice (used in UK tropical medicine teaching, e.g. DTM&H curricula): Tuberculosis, Section 12.5 Immune Reconstitution Inflammatory Syndrome, defining unmasking TB-IRIS as TB not detected before ART, becoming clinically apparent after ART start, most often within the first month, https://medicalguidelines.msf.org/en/viewport/TUB/english/12-5-drug-interactions-20322648.html