Multicentric myofibroblastic sarcoma.

We report a case of synchronous, multicentric low-grade myofibroblastic sarcoma presenting in a 62-year-old man. He initially presented with inflammatory symmetric polyarthritis and adhesive capsulitis of his shoulder and hips bilaterally and did not respond to a trial of disease modifying antirheumatic drugs. Over a period of several years he developed progressive restriction of both knees and nodules on his hands, both knees and back. A biopsy of the nodule on his back was inconclusive and subsequent biopsies on his left and then right knee revealed a spindle cell neoplasm with an infiltrative growth pattern, mitotic figures, positive immunostaining for smooth muscle actin and focal myxoid change consistent with myofibroblastic sarcoma. While myofibroblastic sarcoma has been known to metastasise, to our knowledge, a multifocal presentation of this tumour has not been described previously.