C4d staining as a diagnostic marker in anti-p200 pemphigoid

Here we report the use of C4d as a marker in immunohistochemistry of formalin-fixed paraffin-embedded (FFPE) skin biopsies of 25 patients with confirmed diagnoses of anti-p200 pemphigoid. Fifteen (60%) patients showed linear depositions of C4d along the cutaneous basement membrane zone (BMZ). In 4 of 10 negative samples, a split formation almost along the entire BMZ was seen. Linear deposits of C4d were not detected in any FFPE biopsies from patients with psoriasis (n = 5), lichen planus (n = 4), lupus erythematosus (n = 2), atopic dermatitis (n = 4), pseudolymphoma (n = 4) or cutaneous T-cell lymphoma (n = 4). In one patient with pseudolymphoma, granular deposits of C4d along the BMZ were observed and evaluated as unspecific.