双子出産後の女性における妊娠・授乳関連骨粗しょう症：5年間の経過報告

INTRODUCTION: Pregnancy and lactation-associated osteoporosis (PLO) is a rare but potentially disabling metabolic bone disorder that typically emerges in late pregnancy or the early postpartum period. Because its symptoms often present as common postpartum musculoskeletal complaints, diagnosis is frequently delayed until vertebral fractures are detected. This case report describes a postpartum woman with a twin pregnancy who developed multiple vertebral compression fractures, illustrating the diagnostic challenges, clinical features, and long-term outcomes of PLO. CASE PRESENTATION: A 32-year-old woman presented with persistent low back pain two weeks after cesarean delivery of twins. She had been exclusively breastfeeding and reported inadequate dietary intake and recent weight loss. Thoracolumbar MRI revealed acute compression fractures at T12, L1, and L5. Laboratory evaluation demonstrated low 25-hydroxyvitamin D and parathyroid hormone levels, markedly elevated β-CTX and P1NP, and elevated prolactin. DXA showed significantly reduced lumbar bone mineral density (Z-score -3.25). Clinically significant secondary causes of osteoporosis were excluded based on available testing, and PLO was diagnosed. She was treated with calcium carbonate, calcitriol, alfacalcidol, calcitonin, and intravenous zoledronic acid (initial 5 mg dose during admission, with a second 5 mg dose administered at 1-year follow-up). Following treatment, biochemical markers normalized. At follow-up, MRI confirmed fracture healing, DXA demonstrated improved bone mineral density, and the patient reported complete resolution of symptoms. Long-term evaluation at 5 years showed sustained clinical stability and continued improvement in BMD. CONCLUSION: This case highlights the importance of considering PLO in postpartum women with severe back pain, particularly in the presence of risk factors such as low BMI, inadequate calcium intake, vitamin D insufficiency, exclusive breastfeeding, and twin pregnancy. Early recognition and management can prevent prolonged morbidity and support continued improvement in bone health.