A 42-year-old HIV-positive man stable on tenofovir disoproxil fumarate, lamivudine and efavirenz for 4 years presents with proximal muscle weakness, bone pain, normoglycaemic glycosuria, and serum phosphate of 1.4 mg/dL with a normal calcium and PTH. Urine shows generalized aminoaciduria. The most likely diagnosis is:

• A Tenofovir-induced Fanconi syndrome ✓
• B Multiple myeloma with light chain nephropathy
• C Hyperparathyroidism with renal phosphate leak
• D Distal renal tubular acidosis from efavirenz toxicity

Explanation

Tenofovir disoproxil fumarate accumulates in proximal tubular mitochondria and can cause acquired Fanconi syndrome: proximal tubular dysfunction producing glycosuria despite normal glucose, aminoaciduria, phosphaturia with hypophosphataemia, and metabolic acidosis. Myeloma would show anaemia, raised ESR and monoclonal proteins. Hyperparathyroidism raises PTH with hypercalcaemia, absent here. Efavirenz causes CNS effects and rash, not proximal tubular dysfunction. Switching TDF to tenofovir alafenamide is the corrective step.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.