Dermatomiositis Anti-Mda5 Positive Report of a Case and Literature Review

Abstract

Dermatomyositis (DM) is an autoimmune connective tissue disorder with characteristic skin changes and involvement of different organs and systems, such as muscle, cardiovascular, respiratory and gastrointestinal systems. This condition is characterized by the presence of a myopathic syndrome with bilateral and symmetric weakness predominantly of extensor, proximal muscle groups, respiratory muscles and esophageal involvement, accompanied by characteristic skin disorders. The worldwide incidence is reported at 1 to 6 cases per million inhabitants; predominates in women, with 2.5:1 ratio; and has a bimodal distribution with two peaks, one from 5 to 14 years old and another from 45 to 64 years. The amyopathic form is present in 2 to 18% of all cases of dermatomyositis. Diagnosis is supported by alteration in muscle enzymes, as well as characteristic findings in magnetic resonance imaging (MRI), electromyography (EMG) and autoantibodies. The definitive diagnosis is determined by the histopathological study of both, skin biopsy and affected muscles. The purpose of this case is to review the diagnostic approach from a dermatological point of view, where characteristic lesions gave way to a thorough physical examination looking for signs of a myopathic syndrome; and where despite the elevation of muscle enzymes, findings in electromyography and MRI compatible with myositis, the muscle biopsy was negative. It was the punch biopsy that corroborated the diagnosis, even before the report of anti-MDA-5 antibodies (melanoma differentiation associated Gen 5) that has been linked to a characteristic phenotype of DM that has a higher prevalence of amyopathic disease and a worse prognosis.