Transient Osteoporosis of Pregnancy Affecting the Ankles: A Case Report and Literature Review

Transient osteoporosis of pregnancy (TOP) is a rare condition that typically presents during the third trimester as unexplained lower limb joint pain, most commonly involving the hip. We report an uncommon case of TOP affecting both ankles and provide a literature review of previously reported cases involving the ankle. A 31-year-old Japanese woman developed bilateral ankle pain in the second trimester of pregnancy without any history of trauma. She presented to the orthopedic outpatient clinic in the postpartum period, and her radiographs revealed bilateral diffuse osteopenia, which brought her to our rheumatologic department. Additional radiographic evaluation of the spine and hips showed no evidence of osteopenia. Magnetic resonance imaging of the right ankle, which was obtained for worsening pain, demonstrated bone marrow edema. Blood tests, which evaluated inflammatory markers and alkaline phosphatase, and a musculoskeletal ultrasound were unremarkable. The patient's symptoms gradually resolved with conservative management, including vitamin D supplementation, intermittent use of nonsteroidal anti-inflammatory drugs, and rest. At three months postpartum, radiographs showed partial improvement of osteopenia, whereas MRI still demonstrated bone marrow edema. Follow-up radiographs at eight months demonstrated resolution of the patient's osteopenia, which was consistent with a diagnosis of TOP. We also reviewed previously reported cases of TOP affecting the ankles, identifying eight cases in total. Clinicians should consider the possibility of TOP in pregnant or postpartum women presenting with unexplained joint pain in the lower limbs, including the ankles, even when the pain appears during the second trimester of pregnancy. TOP carries a risk of fracture, making timely and appropriate conservative management essential. Although based on a single case, these findings may indicate that radiographs could reflect recovery earlier than MRI, and may be useful as a follow-up imaging modality in TOP affecting the ankles.