Primary Limb Leiomyosarcoma With Multifocal Musculoskeletal Soft Tissue Metastasis: A Case Report and Literature Review.

Leiomyosarcoma (LMS) is an aggressive soft-tissue sarcoma that may rarely arise in the extremities and metastasize to multiple organs. Primary bone LMS is extremely uncommon and often misdiagnosed due to nonspecific symptoms like pain and swelling. Diagnosis relies on histopathology and immunohistochemistry. Treatment focuses on surgical resection, with chemotherapy and radiotherapy for advanced disease. LMS has a poor prognosis with frequent metastasis, requiring a multidisciplinary approach. A 49-year-old man presented with persistent right knee pain following a fall. Initial imaging suggested a benign lesion, but further investigation due to persistent symptoms led to a malignant spindle-cell tumor diagnosed by biopsy, later confirmed as Grade II leiomyosarcoma (LMS) through immunohistochemistry. After wide surgical excision and radiotherapy, initial follow-up showed no metastases. However, over the following year, imaging detected liver lesions, lung nodules, and a paraspinal mass (indicative of metastatic spread). The patient received chemotherapy but discontinued follow-up for a year, during which the liver masses grew. Biopsy confirmed metastatic LMS, and further chemotherapy was administered. Subsequent scans showed partial response, and surgical removal of liver and paraspinal masses was recommended. The paraspinal mass was excised in early 2024 and confirmed as metastatic LMS. At the latest follow-up, the patient's knee was stable, lungs were clear, and liver lesions were controlled, though he continued to experience pelvic paresthesia and ankle congestion. Ongoing symptoms and the tumor's recurrent nature underline the need for continuous monitoring. The case reflects the importance of an initial multidisciplinary approach and aggressive management to improve outcomes. Due to LMS's rarity and varied presentation, more case reports are essential to better understand its metastatic behavior, improve early detection, and guide treatment strategies. This case contributes valuable insights to the limited literature on metastatic extremity LMS.