A 75-year-old woman with AQP4-IgG-positive NMO was started on weekly intravenous eculizumab following suboptimal response to rituximab with mycophenolate mofetil. Soon after the third infusion, she developed an itchy skin rash involving all extremities that progressed over the subsequent days despite diphenhydramine therapy. Due to progression of the rash, the infusions were discontinued after the fourth one. Her medical history included discoid lupus erythematosus (DLE) in remission for 30 years and Sjogren’s syndrome.

Her physical exam was remarkable for NMO-related deficits (numbness and weakness form the chest down, hyperreflexia and left eye blindness) and the skin rash. All extremities were involved by well-defined, coin-shaped, erythematous papules with varying size and scaling (Fig. 1). Her mucous membranes, nails, scalp, and hair were unaffected. A dermatology evaluation confirmed the clinical impression of this being a drug rash, as did subsequent pathology. Skin biopsy of the left leg revealed a vacuolar interface dermatitis (characterized by vacuolization at the dermal-epidermal junction and lymphocytic inflammation of the epidermis and dermis). Epidermal hyperplasia and dyskeratotic keratinocytes were also present. The preponderance of inflammation over epidermal necrosis favored a medication reaction over erythema multiforme. Findings typical of drug-induced cutaneous lupus (basement membrane thickening and mucin deposition) were absent.

Serological studies showed absence of antinuclear, anti-double-stranded deoxyribonucleic acid, and anti-histone antibodies. Anti-Ro/Sjogren syndrome A and anti-La/Sjogren syndrome B antibodies were positive.

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She was placed on 50 milligrams oral prednisone four times a day for four days with tapering. Prompt clinical improvement was noted with complete resolution at 5 months.