Unusual flaccid blistering with mucosal involvement upon immune checkpoint inhibition

We report the case of a 75-year-old female patient who presented with recent flaccid blistering and intense itching for a week. Concomitantly she also experienced eye redness, for which she applied antibiotic eye drops (gentamicin), and mild oral paresthesia. A preceding common cold had just resolved by the time of presentation. The patient had a medical history of ulcerated melanoma (Breslow's thickness 10 mm) on her upper arm one year before. She was treated according to guidelines with wide excision and sentinel lymph node biopsy. Since then, repeated surgery revealed a total of five metastases in supraclavicular lymph nodes; the stage of disease was IIID (American Joint Committee on Cancer [AJCC 2017]: pT4b pN3c cM0 R0). Molecular pathology analysis of the tumor detected an activating neuroblastoma RAS viral oncogene homolog (NRAS) mutation, but no druggable BRAF gene mutation; the patient therefore received an adjuvant treatment with nivolumab. The first dose was given one month before formation of the skin lesions. Apart from hypertension and hypothyroidism there was no relevant comorbidity.