Infiltrations of eosinophils are found in affected muscle tissue and fascia. The cause is unknown. Symptoms include tenderness and swelling of arms and legs, joint contractures, bone apins, muscle aches, and muscle weakness. Some may complain of carpal tunnel syndrome symptoms with numbness and tingling in the hands. Diagnosis is made by tissue biopsy .
Treatment includes systemic corticosteroids .
The illness can last for 3 to 5 years and then ususally resolves.