Is there a linear IgM dermatosis? Significance of linear IgM junctional staining in cutaneous immunopathology

A linear IgM staining of the basal membrane zone (BMZ) is difficult to classify as denoting any known dermatological disorder. In a group of 2,771 persons biopsied for routine immunofluorescence microscopy, 25 cases (0.9%) with this phenomenon were found, whereas the incidences of bullous pemphigoid and linear IgA dermatosis in this group were resp. 1.2% and 0.01%. The IF patterns, serological data and clinical pictures of the linear IgM group were reviewed for a common denominator. One patient had bullous pemphigoid. The others showed a variety of symptoms and diagnoses. In the majority of cases the linear IgM deposits were monoclonal, a feature not understood. Immunoelectronmicroscopy performed in one patient proved IgM deposits below the basal lamina. It is concluded that there is no such entity as a linear IgM dermatosis and furthermore, that linear IgM staining at the BMZ has to be distinguished from related patterns such as the granular BMZ deposits ('lupus band') in SLE.