Adult-type dermatomyositis with secondary lymphoid follicles harbouring reactive B-cells component

•Dermatomyositis is an autoimmune disease characterized by lesions in skin and inflammatory infiltrates of the muscle.•Its association with ectopic lymphoid structures (ELS) is very rare typical variant.•The role of B-cells in lymphoid follicle is not linked to an unfavorable prognosis. Dermatomyositis (DM) is an immune-mediated inflammatory disease characterized by pathognomic lesions in skin and skeletal muscle including lymphocytic infiltrates. It rarely presents with ectopic lymphoid structures, as other autoimmune and chronic inflammatory diseases. We describe a case of a 47-year-old male, who presented clinically with proximal muscle weakness, skin rash and elevated creatin kinase (CK) levels. The muscle biopsy revealed inflammatory myopathy, with perifascicular pathology, and scattered ectopic lymphoid follicles-like structures harboring reactive B-cells. Clonality analysis of B-cells using polymerase chain reaction ruled out malignant lymphoma. The patient responded favorably to steroid therapy, and his muscle weakness improved. In conclusion, the clinical and histopathologic features of DM can be atypical, and the presence of lymphoid follicles, although rare, is not inevitably linked to an unfavorable prognosis.