A Rare Case of Drug-Induced Sweet Syndrome After Pembrolizumab Therapy.

Sweet syndrome is an uncommon inflammatory disorder characterized by the abrupt appearance of painful, erythematous papules, plaques, or nodules on the skin. Fever and leukocytosis frequently accompany the cutaneous lesions. In addition, involvement of the eyes, musculoskeletal system, and internal organs may occur. Sweet syndrome has been associated with a broad range of disorders. There are three subtypes: classical Sweet syndrome, malignancy-associated Sweet syndrome, and drug-induced Sweet syndrome. Classical Sweet syndrome is not associated with malignancy or drugs. It is essentially associated with an upper respiratory infection, gastrointestinal infection, inflammatory bowel disease, and pregnancy. Malignancy-associated Sweet syndrome is associated with hematologic malignancy more than solid malignancy, most commonly with acute myeloid leukemia. Drug-induced Sweet syndrome usually develops approximately two weeks after drug exposure, in patients who lack a prior history of exposure to the inciting drug. Here we are discussing our patient, a 68-year-old male who presented eight weeks after starting chemotherapy with pemetrexed, carboplatin, and pembrolizumab for left lung adenocarcinoma with macular rash. On further investigation with biopsy was found to have neutrophilic dermatitis, hence being diagnosed with drug-induced Sweet syndrome. Histopathology revealed a dermis with infiltration of neutrophils with lekocytoclasia.