Persistent Psoriasiform Dermatitis--A Presentation of Psoriasiform Pemphigus Foliaceus: A Case Report

Summary: A 55-year-old male with a history of Lyme disease and a three-year history of psoriasis presented to clinic with erythroderma. Biopsy performed four months prior reportedly showed psoriasiform dermatitis. His prior treatment regimen included risankizumab and prednisone, and notably, his psoriasis significantly worsened when the prednisone dose was tapered.  On physical exam, there were erythematous scaly plaques involving 95% of body surface area, including the nails. A skin punch biopsy was performed, which showed psoriasiform epidermal hyperplasia with spongiosis and superficial dermal inflammation including lymphocytes, plasma cells, and eosinophils. Additionally, superficial epidermal and subcorneal acantholysis was present, raising concerns for pemphigus foliaceus. Immunohistochemistry showed superficial epidermal intercellular positivity for IgG4. With the histopathologic features concerning for pemphigus foliaceus, re-biopsy was performed for direct immunofluorescence, which showed epidermal intercellular positivity for IgG, IgG4 and C3. Pemphigus antibody panel showed IgG desmoglein 1 antibody level of 81,000 U/mL (normal/negative: less than 14 U/mL). Taken together, the diagnosis of psoriasiform pemphigus foliaceus was rendered, which is a member of pemphigus family that can lead to severe exfoliative erythroderma. This case illustrates the importance of keeping this rare differential diagnosis in mind when evaluating biopsies with the history of persistent psoriasis with erythroderma.