The diagnoses of autoimmune blistering diseases, including bullous pemphigoid (BP) and pemphigus, are confirmed based on a combination of characteristic clinical findings, histological features, and immunological findings. Immunological tests are classified as direct immune fluorescence (DIF) tests, which detect tissue-bound autoantibodies, and serological tests, such as indirect immunofluorescence (IIF), enzyme-linked immunosorbent assays (ELISA), and immunoblotting. We previously investigated the tissue-bound immunoglobulin (Ig) isotypes in 100 cases of BP and found that 17% of patients demonstrated IgM deposits at the dermoepidermal junction (DEJ). 1 However, they showed IgG deposits as well as IgM, and there were no patients with only IgM autoantibodies. This is because IgG autoantibodies are mandatory for diagnosing BP. 2 Recently, the concept of IgM pemphigoid has been proposed. 3 We present a case showing histological subepidermal blistering associated with IgM deposits at the DEJ.

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Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease. Although the pathomechanism of BP onset has yet to be elucidated in detail, BP autoantibodies targeting two hemidesmosomal components, BP180 and BP230, are known to play a pivotal role in BP pathogenesis. Thus, the detection and measurement of BP autoantibodies are necessary for diagnosing BP and monitoring the disease activity. Immune assays such as immunofluorescence microscopy, immunoblotting, and ELISAs using BP180 and BP230 detect BP autoantibodies in most BP cases with high specificity; however, BP autoantibodies are sometimes detected in BP patients before the onset of this disease. BP autoantibodies that are detected in patients without typical tense blisters are defined as “preclinical BP autoantibodies”. These preclinical BP autoantibodies are detected even in a low percentage of normal healthy individuals. Although the importance of preclinical BP autoantibodies remains elusive, these autoantibodies might be a potential risk factor for subsequent BP development. Therefore, previous comparative epidemiological studies have focused on the prevalence of preclinical BP autoantibodies in populations susceptible to BP (e.g., the elderly) or in diseases with a higher risk of comorbid BP. This mini-review summarizes the literature on the prevalence of preclinical BP autoantibodies in patients with various conditions and diseases, and we discuss the significance of preclinical BP autoantibody detection.