Tenofovir-induced hypophosphatemic osteomalacia: how do bone mineral density, trabecular bone score and proximal hip geometry change with treatment?

SUMMARY: Tenofovir-induced osteomalacia secondary to proximal renal tubular dysfunction is not an uncommon complication known to occur. A 46-year-old woman was referred for the evaluation of osteoporosis which was diagnosed elsewhere. She had polyarthralgia, bony pains and proximal muscle weakness of 1 year duration. She was diagnosed to have HIV infection and was on antiretroviral therapy that consisted of tenofovir, lamivudine and efavirenz for the past 12 years. She had attained menopause 5 years back. On examination, she had bone tenderness, proximal myopathy and painful restriction of movement of her lower limbs. Investigations showed features of renal tubular acidosis, hypophosphatemia and raised alkaline phosphatase that were suggestive of osteomalacia. X-ray of the pelvis showed diffuse osteopenia and an MRI of the pelvis done showed multiple insufficiency fractures involving the head of femur on both sides. Following this, her tenofovir-based regimen was changed to abacavir, efavirenz and lamivudine with addition of neutral phosphate supplements and calcitriol. On follow-up after 6 months, she had significant improvement in her symptoms as well as in the bone mineral density at the lumbar spine (33.2%), femoral neck (27.6%), trabecular bone score (13.2%) and reduction in the buckling ratio at the narrow neck (6.3%), inter-trochanteric region (34%) and femoral shaft (28.8%). Tenofovir-induced osteomalacia is encountered in individuals on prolonged treatment with tenofovir. Treatment consists of changing to a non-tenofovir-based regimen, as well as supplementation of phosphate and calcitriol. Treatment results in remarkable improvement in symptoms and most densitometric indices. LEARNING POINTS: Tenofovir is a nucleotide reverse transcriptase inhibitor (NRTI) and is a major drug in the treatment of retroviral and hepatitis B infections. Tenofovir-related hypophosphatemic osteomalacia is related to proximal tubulopathy and is not an uncommon occurrence. Treatment mandates changing to a non-tenofovir-based regimen with supplementation of neutral phosphate and calcitriol. Treatment results in a significant improvement in bone mineral density, trabecular bone score and hip geometric parameters.