MR imaging of infiltrative muscle involvement with Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) consists of three clinical syndromes of varying severity resulting from basic cellular defect leading to lipid deposition within histiocytes. Radiologically, bone lesions are similar in all three forms of LCH and are due to bone destruction. An eosinophilic granuloma of the bone can involve skeletal muscle by direct extension from the bone. However, skeletal muscle involvement is rare and is not reported on MR imaging previously in the English literature. Our case not only shows biopsy-proven muscle involvement by LCH but also reports the first diffuse nodular pattern of muscle involvement by LCH.