Transient osteoporosis of the hip in pregnancy associated with generalized low bone mineral density--a case report.

Transient osteoporosis of the hip (TOH) in pregnancy is characterized by severe pain in unilateral or bilateral hips and has been diagnosed as localized osteopenia. However, we evaluated a case of unilateral TOH with generalized profound osteoporosis involving both the hips and the lumbar vertebrae by dual-energy X-ray absorptiometry. The diagnosis was based on the clinical course and confirmed by magnetic resonance imaging. Three-dimensional helical computed tomography (3D-CT), which has not been used in patients with TOH, revealed a markedly thin bilateral proximal femoral cortex, particularly in the symptomatic femoral head. Despite the difference in the severity of bone destruction between the two femora, they both showed the same pattern of damage on 3D-CT. Furthermore, despite continuing treatment with the same dose of alendronate and calcitriol, a high rate of bone mineral density gain, involving both the femora and lumbar vertebrae, was limited to the early postpartum months. A majority of reported female patients with TOH are pregnant. Thus, the association between TOH and pregnancy was not considered to be fortuitous, and chemical or hormonal factors related to pregnancy may play an etiologic role in this disease. The possible etiologies of TOH in pregnancy are also discussed.