BACKGROUND: Although a linear IgM dermatosis of pregnancy has been reported, other authors have not found evidence for a distinct linear IgM dermatosis. OBJECTIVE: We set out to determine whether or not continuous dermoepidermal junction IgM deposition detected by direct immunofluorescence was indicative of a specific disease. METHODS: We collected nine cases during a 9-year period in which biopsy specimens for direct immunofluorescence revealed continuous linear IgM at the dermoepidermal junction in the absence of other immunoglobulins. In all of these cases the medical record was available for review. RESULTS: Clinical correlation revealed that these patients had a heterogeneous group of diseases with urticaria and leukocytoclastic vasculitis being most common. No diagnostic specificity could be ascribed to the linear IgM pattern, although six of our nine cases could be considered manifestations of a hypersensitivity response (e.g., urticaria, leukocytoclastic vasculitis, pigmented purpuric dermatosis, or hypersensitivity dermatitis). CONCLUSION: Pathologists and dermatologists should be aware that linear IgM can be seen in a variety of clinical settings. The etiopathogenic significance of this finding, if any, remains to be determined. At present, the finding must be viewed as nonspecific.
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