Introduction: Polyarthritis , also called periarthritis nodosa (PAN) is a disease of small and medium-sized arthritis. In a subset of patient with PAN, however, the disease process remains localized within a single organ or a precise anatomical area.

Case Report: A 29-year old man was referred to our department for the pain in the 2/3 upper of the external face of his left arm. The radiography was consistent with soft tissue swelling and periosteal reaction. MRI showed abnormal signal involving muscle in some parts. The surgical biopsy was done.

Conclusion: Pathological study on the specimen supported the PAN (polyarthritis nodosa) so prednisolone 1 mg/kg was started and provided relief of pain and myalgia .