Bullous Pemphigoid: A 10-Year Study of Discordant Results on Direct Immunofluorescence.

BACKGROUND: Bullous pemphigoid (BP) is the most common subepidermal autoimmune disorder characterized by tense bullae. It is associated with circulating autoantibodies against BP antigen-1 and BP antigen-2. Diagnosis is based upon clinical, histopathologic, and immunopathologic examination. Direct immunofluorescence (DIF) of perilesional skin highlights C3 with or without IgG in a linear pattern along the basement membrane. OBJECTIVES: We hypothesized that repeat biopsies may be required for a definitive DIF diagnosis of BP, as initial DIF evaluation may result in a false-negative result. METHODS: A retrospective chart review was conducted on 1143 specimens collected for evaluation for BP. Cases from 2 Vancouver Coastal Health Authority laboratories from 2006 to 2016 were reviewed. Results were interpreted as positive, negative, or indeterminate based on pathologic description and specimen quality. RESULTS: After meeting the inclusion criteria, 739 specimens were further evaluated. There were 289 cases of BP in the 10-year period. Five patients (1.73%; 95% confidence interval [CI], 1.50-1.96) required a second biopsy to support a BP diagnosis, and within this group, 1.04% of the 289 (95% CI, 0.811-1.27) were true successive negative-to-positive DIF results. CONCLUSIONS: DIF is the most reliable test used to diagnose BP; however, a small percentage of patients will initially have a negative result. False-negative or indeterminate results may be due to specimen sampling from lesional skin or due to a subthreshold quantity of immune complexes in the skin. Repeat biopsy is warranted despite an initial negative DIF if BP is clinically suspected.