Diagnose This (October 19, 2020)

What would be your leading diagnosis in a patient with elevated ACE levels and hilar lymphadenopathy? 

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The light microscopic image depicts a non-necrotizing granuloma which, in the clinical context, would be compatible with Sarcoidosis. Histologic features of Sarcoidosis typically include well-formed non-caseating granulomas composed of epithelioid histiocytes and multinucleated giant cells along with an active tubulointerstitial nephritis typically composed of a lymphoplasmacytic infiltrate, rarely containing eosinophils. Interestingly, rare cases of this disease have shown a concomitant glomerular disease, the most common being Membranous nephropathy. Of important note, the biopsy findings of a non-necrotizing granulomatous tubulointerstitial nephritis are not specific to Sarcoidosis and the differential diagnosis would also include drug/hypersensitivity reaction (most common), vasculitis, and infection (i.e. mycobacterial, fungal).