This vignette is deliberately built to look like pulmonary tuberculosis - chronic constitutional symptoms, cavitary lesions, caseating granulomas - yet the standout details point to histoplasmosis.
Two features steer the diagnosis. First, the patient is from Assam, part of the North-East Indian belt where Histoplasma capsulatum is endemic. Second, the biopsy is rich in histiocytes; this dimorphic fungus survives and multiplies as tiny yeasts within macrophages, so a histiocyte-laden, necrotising granuloma is its signature. Special stains (GMS, PAS) reveal the intracellular yeast forms.
The competitors fall away on histology: sarcoid granulomas are characteristically non-caseating; aspergillosis shows septate branching hyphae filling a cavity rather than intracellular yeast; and granulomatosis with polyangiitis produces necrotising vasculitis with geographic necrosis and a sinonasal/renal flavour.
\[\boxed{\text{Assam + TB-like caseating histiocytic granuloma} \Rightarrow \text{Histoplasmosis}}\]