Teriparatide treatment in an adult patient with hypophosphatasia exposed to bisphosphonate and revealed by bilateral atypical fractures.

Atypical femoral fractures are defined as atraumatic fractures located in the subtrochanteric region or femoral shaft. They have been mainly reported in patients taking bisphosphonates. We report the case of a 67-year-old female with osteoporosis treated by alendronate during ten years. Radiographies showed atypical femoral fractures. Serum levels of total and bone-specific alkaline phosphatase were low. In order to accelerate bone healing, teriparatide was introduced. After one year of teriparatide treatment, pain and functional difficulty have decreased, and alkaline phosphatase levels were normalized. In view of this history of recurrent fractures, of atypical femoral fractures, of early spontaneous loss of teeth, and of low serum total and bone-specific alkaline phosphatase levels, the diagnosis of hypophosphatasia has been considered and confirmed by genetic research. Other conditions than exposure to anti-resorptive therapies may promote atypical femoral fractures, such as in conditions associated with abnormal bone structures, as hypophosphatasia, a rare inherited bone metabolism disorder. A few case reports have reported adult hypophosphatasia treated by teriparatide with a good efficacy on bone pain and consolidation but with mixed results on biological markers. Teriparatide may be therefore a treatment option in adult hypophosphatasia. ALP levels should be carefully checked among osteoporotic patients and specially before introducing a bone resorption inhibitor. Low alkaline phosphatase levels have to be taken into account and an evocative history of hypophosphatasia has to be sought because this condition may expose patients to develop atypical femoral fractures during bisphosphonate treatment.