Myosite focale : une maladie méconnue

Abstract

Focal myositis are inflammatory muscle diseases of unknown origin. At the opposite from the other idiopathic inflammatory myopathies, they are restricted to a single muscle or to a muscle group. They are not associated with extramuscular manifestations, and they have a good prognosis without any treatment. They are characterized by a localized swelling affecting mostly lower limbs. The pseudo-tumor can be painful, but is not associated with a muscle weakness. Creatine kinase level is normal. Muscle MRI shows an inflammation restricted to a muscle or a muscle group. Muscle biopsy and pathological analysis remain necessary for the diagnosis, showing inflammatory infiltrates composed by macrophages and lymphocytes without any specific distribution within the muscle. Focal overexpression of HLA-1 by the muscle fibers is frequently observed. The muscle biopsy permits to rule out differential diagnosis such a malignancy (sarcoma). Spontaneous remission occurs within weeks or months after the first symptoms, relapse is unusual.

Focal myositis of the sternocleidomastoid muscle: a rare and uncommon cause of cervical mass

“…It could affect one single muscle (as in our patient) or a muscle group and can present in patients of all ages. Clinically, patients report a subcutaneous mass progressively increasing in size (for weeks or months) and mostly affecting lower limbs -contrary to the case presented -and it is painful in approximately half of the reported cases [2,7] . In contrast to other rheumatic or idiopathic myopathies, extramuscular manifestations are not common as in our case, and patients remain in a good general condition.…”

“…MRI shows an inflammation restricted to a muscle, and muscle biopsy shows inflammatory infiltrates composed of macrophages and lymphocytes without any specific distribution within the muscle, permitting the clinician to rule out malignancy or infection. Evolution is spontaneously favourable without any treatment, and relapse is unusual [2,7] .…”

“…There is no diagnostic biological tool as the creatine kinase level and autoantibodies are normal, and inflammatory markers can be slightly elevated [2,7,8] . Differential diagnosis is wide and includes among others venous thromboembolic disease, soft tissue infection, malignant soft tissue tumours (liposarcoma, undifferentiated sarcoma, leiomyosarcoma, myxofibrosarcoma, angiosarcoma and fibrosarcoma), benign tumours, trauma, calf myositis, myositis ossificans and diabetic myonecrosis [2] . There has been controversy over whether idiopathic focal myositis was a part of systemic polymyositis.…”

“…The muscle enhancement remained has not been included in the international classifications of idiopathic inflammatory myopathies; it therefore appears to be a rare entity that is still poorly understood [2] .…”