Hypophosphatemic Osteomalacia Related to Tenofovir Toxicity

Program: Abstracts - Orals, Poster Previews, and Posters
Session: FRI 368-390-Metabolic Bone Disease Case Reports (posters)
Clinical
Friday, April 1, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board FRI 380
Monica Ashley Gomberg*1, Peter J Veldkamp1 and R Harsha Rao2
1University of Pittsburgh Medical Center, Pittsburgh, PA, 2Division of Endocrinology, VA Pittsburgh Healthcare System, Pittsburgh, PA
Background:

Fanconi’s syndrome from proximal tubular damage is a rare complication of Tenofovir (TDF) therapy for HIV/HBV infections. We describe a patient with severe osteomalacia and hypophosphatemia from Fanconi’s syndrome, who responded rapidly to TDF withdrawal, oral phosphate (PO4) repletion and calcitriol.

Clinical Case:

A 54-year old female with HIV controlled on Atripla (efavirenz, emtricitabine, TDF) and on daily vitamin D (400 IU) and calcium (600mg) supplements for 10 years, presented with intractable hip and lower extremity pain and weakness, progressive difficulty ambulating, and repeated falls over 18 months. Mild proteinuria was present for several years, but glycosuria, hypophosphatemia (1.7, normal range [NR] 2.5-4.6) and worsening CKD (eGFR 31ml/min, down from 47ml/min 9 months earlier) had developed recently.

Endocrinology was consulted for “unexplained hypophosphatemia” during hospitalization for disabling pain. Metabolic bone studies revealed hyperchloremic non-gap metabolic acidosis consistent with proximal RTA, with high alkaline phosphatase (258IU/dl, NR 38-126), high PTH (80 pg/ml, NR 10-65), and phosphaturia (fractional PO4 excretion 62.3%, NR <5%), but normal Calcium 8.6mg/dl (NR 8.4-10.2) and vitamin D 25-OH 33ng/ml (NR 25-100, “adequate” >30), 1,25(OH)2 48pg/ml (NR 18-72). X-rays showed bilateral subtrochanteric Looser’s Zones and non-displaced proximal diaphysial fractures of 1st and 3rd metatarsals. Bone scan showed increased uptake in lesser trochanters, 1st and 3rd metatarsals, distal right femur, and right ankle. TDF-related Fanconi’s syndrome causing hypophosphatemia and osteomalacia was suspected and TDF replaced along with oral PO4repletion and calcitriol supplementation. Complete clinical, biochemical and radiographic resolution was achieved in 14 weeks, at which time supplementation was discontinued and maintenance cholecalciferol (2000 IU/ day) started. DXA showed appendicular osteopenia distally (forearm T score -2.4) but not proximally (femoral neck -0.9, total hip -0.3), and no axial osteopenia (L1-L4 2.1), consistent with osteomalacia.

Conclusion:

The diagnosis of TDF-induced Fanconi’s syndrome is based on typical findings of glycosuria, proteinuria, and phosphaturia (high fractional PO4 excretion), as well as hypophosphatemia. Regular urine and blood tests to screen for these features facilitates early diagnosis of Fanconi’s syndrome. Furthermore, recognition of osteomalacia depends on radiographic screening for pseudofractures in the context of proximal (Type 2) RTA and typical musculoskeletal symptoms. Notably, elevations in eGFR, which reflect glomerular, not tubular dysfunction, can be delayed by several years in Fanconi’s syndrome. Removal of the inciting agent is critical for clinical resolution, which may occur well before normalization of biochemical or radiographic abnormalities.

Nothing to Disclose: MAG, PJV, RHR

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