title: Focal myositis: A review.
abstract: Amongst the heterogeneous group of inflammatory myopathies, focal myositis stands as a rare and benign dysimmune disease. Although it can be associated with root and/or nerve lesions, traumatic muscle lesions and autoimmune diseases, its triggering factors remain poorly understood. Defined as an isolated inflammatory pseudotumour usually restricted to one skeletal muscle, clinical presentation of focal myositis is that of a rapidly growing solitary mass within a single muscle, usually in the lower limbs. Electromyography shows spontaneous activity associated with a myopathic pattern. MRI reveals a contrast enhanced enlarged muscle appearing hyper-intense on FAT-SAT T2 weighted images. Adjacent structures are spared and there are no calcifications. Serum creatine kinase (CK) levels are usually moderately augmented and biological markers of systemic inflammation are absent in most cases. Pathological histological features include marked variation in fibre size, inflammatory infiltrates mostly composed of T CD4+ lymphocytes and macrophages, degenerating/regenerating fibres and interstitial fibrosis. Differential diagnoses are numerous and include myositis of other origin with focal onset. Steroid treatment should be reserved for patients who present with major pain, nerve lesions, associated autoimmune disease, or elevated C reactive protein or CK.
authors.affiliation: Department of Functional Neurology and Epileptology, Pierre Wertheimer Neurology University Hospital, 69 Bdv Pinel, 69677 Bron-Cedex, France; University Claude Bernard Lyon-I, France. Electronic address: perrine.devic@chu-lyon.fr.
authors.forename: P
authors.initials: P
authors.lastname: Devic
authors.affiliation: University Claude Bernard Lyon-I, France; Department of Clinical Immunology, Pavillon O, Edouard Herriot University Hospital, 5 place d'Arsonval, 69437 Lyon Cedex 03, France; NeuroMyoGen Institute, CNRS UMR 5310 - INSERM U1217, France.
authors.forename: L
authors.initials: L
authors.lastname: Gallay
authors.affiliation: University Claude Bernard Lyon-I, France; NeuroMyoGen Institute, CNRS UMR 5310 - INSERM U1217, France; Department of Pathology, Lyon East University Hospital, 69 Bdv Pinel, 69677 Bron-Cedex, France.
authors.forename: N
authors.initials: N
authors.lastname: Streichenberger
authors.affiliation: Department of Neurology, Croix-Rousse University Hospital, 103 Grande Rue de la Croix-Rousse, 69004 Lyon, France.
authors.forename: P
authors.initials: P
authors.lastname: Petiot
mesh_terms: D006801:Humans; D009220:Myositis / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology / Q000628:therapy
keywords: Focal myositis; Inflammatory myopathy; Intramuscular tumour; Muscle biopsy