DIF Distinguishes Lupus Erythematosus from Dermatomyositis

Lupus erythematosus (LE) and dermatomyositis (DM) are sometimes difficult to distinguish purely on clinical grounds. The histologic findings can also be similar and difficult to differentiate. These authors compared the findings of direct and indirect immunofluorescence in 31 patients with well-documented LE and 24 patients with DM. They used a panel of routine antibodies directed against IgG, IgA, IgM, C3, and fibrin, as well as antibodies against the C_5-9 membrane attack complex. All biopsies were from lesional skin.

A positive lupus band test (LBT), which was defined as staining with IgG or IgM along the dermal epidermal junction, was seen in the majority of patients with LE but only rarely in those with DM. Only a minority of patients wi…