A Severe Necrotic Intertriginous Eruption in a Patient on Pembrolizumab for Advanced Melanoma

A 62-year-old woman with hypertension, hypercholesterolaemia, increased body mass index and preexisting hidradenitis suppurativa (HS) developed unresectable locally advanced melanoma and commenced pembrolizumab 400mg intravenously every six weeks.Eight months after commencing pembrolizumab, she developed progressive skin breakdown affecting the suprapubic and groin creases bilaterally.There were no nodules or abscesses suggestive of active HS.The eruption was initially diagnosed as chronic intertrigo and treated with topical clotrimazole.On subsequent dermatology review, she had extensive erythema and superficial erosion affecting all intertriginous areas alongside hypopigmented wrinkled areas of skin.Differential diagnoses from the treating dermatology consultant included pembrolizumab-associated vitiligo and extragenital lichen sclerosus; the presentation was not consistent with HS.A punch biopsy was recommended but initially declined because of significant surgical anxiety.The eruption continued to deteriorate, resulting in hospital admission with severe pain, fatigue and profound functional impairment.Examination on hospital admission demonstrated widespread erosive, inflammatory, hypopigmented and atrophic changes involving multiple intertriginous sites.Punch biopsy during hospital admission revealed almost complete epidermal necrosis with a prominent neutrophilic infiltrate, without features of lichen sclerosus or immunobullous disease; histopathological findings were not consistent with her pre-existing diagnosis of HS.Skin swabs grew a heavy growth of Staphylococcus aureus consistent with superimposed bacterial infection.A severe pembrolizumab-associated immune-mediated cutaneous toxicity with superimposed bacterial infection was considered the likely diagnosis based on clinical features, serology, microbiology and histopathology.The toxicity was graded as 3-4 according to the Common Terminology Criteria for Adverse Events (CTCAE) by the treating medical oncology consultant.Pembrolizumab was discontinued and intravenous methylprednisolone 2mg/kg was initiated, followed by a slow oral prednisolone taper.She received a short course of oral antibiotics for superadded bacterial infection and intensive wound care.The eruption improved significantly after the start of intravenous steroids, although she required a month-long hospital admission with ongoing community nursing and rehabilitation following discharge.