Case report: Atypical SJS/TEN-like fulminant pemphigus vulgaris: diagnostic challenges and the potential impact of anti-Dsg1 titers and CMV reactivation.

Pemphigus vulgaris (PV) is a chronic autoimmune blistering disease characterized by intraepidermal flaccid blisters of the skin and mucous membranes. Although typically chronic and relapsing, rare fulminant variants have been described. We report a life-threatening case of PV in a previously healthy 55-year-old woman who developed a rapidly progressive, Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN)-like phenotype with extensive epidermal detachment and mucocutaneous involvement. Histopathological analysis demonstrated suprabasal acantholysis, and direct immunofluorescence showed intercellular IgG and C3 deposition. Serology revealed markedly elevated anti-Desmoglein-1 (107.5 IU/mL) and modest anti-Desmoglein-3 titers (9.6 IU/mL). The clinical course was complicated by Cytomegalovirus reactivation, while malignancy screening remained negative. Treatment with rituximab and intravenous immunoglobulin led to rapid re-epithelialization and clinical stabilization. This case expands the clinical spectrum of PV and underscores diagnostic and therapeutic challenges posed by fulminant autoimmune blistering disease exhibiting overlapping features. As rat-bladder indirect immunofluorescence and extended plakin serology were not available, a paraneoplastic pemphigus (PNP)-spectrum disorder could not be formally excluded, although the clinical, histological, and serological picture strongly favored PV. We propose that markedly elevated anti-Dsg1 antibodies, complement activation, and CMV reactivation may each have contributed to this severe phenotype.