Abstract
Nivolumab is a monoclonal immunoglobulin G antibody blocking programmed death receptor-1 (PD-1) that promotes the restoration of the natural T-cell-mediated immune response against cancer cells; however, it also causes a number of autoimmune-related adverse events (irAEs) that often involve the endocrine system. The present report describes a 71-year-old man with clear cell renal cell carcinoma metastasis in the lung. Following the 14th course of nivolumab therapy, the patient complained of general malaise, loss of appetite and mild consciousness disturbance. Laboratory tests revealed a severely elevated eosinophil ratio (26.2%) and low sodium value (122 mmol/l). Endocrine system tests revealed that the patient's adrenocorticotropic hormone (ACTH; 4.5 pg/ml) and cortisol (0.1 µg/dl) levels were lower than normal, while those of other pituitary hormones were higher than normal. This case was therefore diagnosed as isolated ACTH deficiency induced by nivolumab. Magnetic resonance imaging (MRI) showed normal pituitary glands. Hydrocortisone replacement therapy improved the clinical symptoms early and enabled the patient to restart nivolumab therapy. Isolated ACTH deficiency due to nivolumab, a PD-1 immune checkpoint inhibitor antibody, is a rare occurrence. This report may be useful for avoiding delays in the diagnosis and treatment of this life-threatening irAE even if no pituitary abnormalities are identified via MRI.