# Tenofovir-Associated Hypophosphatemic Osteomalacia in an HIV-Infected Patient: A Case Report

## TL;DR

A patient with HIV developed bone disease due to a medication called tenofovir, which caused low phosphate levels and improved after treatment adjustments.

## Contribution

This case report highlights hypophosphatemic osteomalacia as a rare but important side effect of tenofovir therapy.

## Key findings

- The patient showed marked hypophosphatemia, phosphaturia, and elevated alkaline phosphatase and parathyroid hormone levels.
- Discontinuation of tenofovir and phosphate and vitamin D supplementation led to significant clinical and laboratory improvement.
- Tenofovir-associated hypophosphatemic osteomalacia can present with musculoskeletal symptoms mimicking rheumatologic disorders.

## Abstract

Hypophosphatemic osteomalacia is a rare metabolic bone disease in adults, most commonly caused by acquired conditions. Clinically, it may present with widespread musculoskeletal pain, proximal muscle weakness, and gait disturbance, often mimicking rheumatologic disorders. Tenofovir disoproxil fumarate, a widely used nucleotide reverse transcriptase inhibitor in the treatment of human immunodeficiency virus infection, may rarely cause hypophosphatemia and osteomalacia due to proximal renal tubular dysfunction.

We report a 33-year-old male patient who presented with progressively worsening diffuse bone and muscle pain, proximal muscle weakness, and difficulty walking over one year and was diagnosed with tenofovir-associated hypophosphatemic osteomalacia. Laboratory evaluation revealed marked hypophosphatemia, phosphaturia, and elevated alkaline phosphatase and parathyroid hormone levels. After discontinuation of tenofovir and initiation of phosphate and active vitamin D supplementation, both clinical symptoms and laboratory abnormalities improved significantly.

This case highlights hypophosphatemic osteomalacia as a potentially overlooked complication of tenofovir therapy.