Primary Osseous Leiomyosarcoma of Talus Mimicking Idiopathic Transient Osteoporosis: A Case Report and Literature Review.

Primary leiomyosarcoma of the bone (LMSB) is an exceptionally rare malignant bone tumor. We report a case of a 60-year-old woman with LMSB of the talus initially misdiagnosed as idiopathic transient osteoporosis of the talus based on clinical and initial MRI findings, which showed extensive bone marrow edema without soft tissue invasion. Despite initial improvement with off-loading treatment, the patient's symptoms recurred, and subsequent imaging revealed progression and soft tissue involvement. A biopsy confirmed grade 1-2 leiomyosarcoma. Wide resection and reconstruction with a custom-made total talar prosthesis were performed, but local recurrence necessitated a transtibial amputation eight months postoperatively. This case highlights the diagnostic challenge of early-stage LMSB of the talus, which can mimic idiopathic transient osteoporosis on MRI. Clinicians should be aware of this potential pitfall, as the treatment strategies for these two conditions are diametrically opposed: conservative management for idiopathic transient osteoporosis versus prompt surgical resection for LMSB to improve prognosis. Repeated imaging and a high index of suspicion are crucial for timely and accurate diagnosis of this rare and aggressive tumor.