Atypical Fracture From Bisphosphonate Use in Hypophosphatasia With Improved Bone Response to Teriparatide Therapy.

Hypophosphatasia is a rare metabolic bone disorder that is often misdiagnosed. We present the case of a middle-aged woman initially misdiagnosed with rickets and later as osteogenesis imperfecta and treated with zoledronate, after which she developed atypical femoral fractures. After switching to teriparatide therapy, her bone mineral density improved significantly. This case underscores that persistently low alkaline phosphatase with fragility or atypical fractures should prompt evaluation for hypophosphatasia and that antiresorptives (eg, bisphosphonates) may precipitate atypical fractures in this condition and should be avoided. Disease-specific therapy is enzyme replacement with asfotase alfa; anabolic therapy may improve bone mineral density in selected adults when asfotase alfa is unavailable.