The lymphoid follicle variant of dermatomyositis

To investigate the clinical and morphologic spectrum of early adult-onset dermatomyositis (DM), an inflammatory disease that affects small vessels of the muscle and the skin.

Histologic evaluation of frozen muscle samples was employed to visualize the cellular organization of ectopic lymphoid structures in muscle biopsies obtained from 2 patients diagnosed with DM. Clinical presentation and morphologic features, as well as treatment and follow-up, were assessed and documented. Electron microscopy was used to confirm the light microscopic diagnosis of DM. Clonality analysis of B-cell populations using PCR was performed.

Muscle biopsy of both patients fulfilled the morphologic European Neuromuscular Centre criteria of DM. Analyses of muscle biopsy samples revealed ectopic lymphoid follicle-like structures that showed a remarkable similarity to secondary lymphoid organs (SLOs) with distinct T- and B-cell compartmentalization. Our 2 patients exhibited an atypical and mild clinical presentation and responded favorably to therapy.

The clinical and histopathologic features of DM can be atypical, and the presence of SLOs is not inevitably linked to an unfavorable prognosis.