PTHrP ‐Producing Renal Cell Carcinoma Presenting as Rapidly Progressive Cognitive Impairment: A Case Report

Introduction: Humoral hypercalcemia of malignancy (HCM) caused by parathyroid hormone-related peptide (PTHrP) is a common paraneoplastic syndrome, and renal cell carcinoma (RCC) is one of the main causes. However, initial presentation with rapidly progressive cognitive decline is rare. Case Presentation: A 68-year-old woman was presented with a rapidly progressive cognitive impairment. Laboratory tests revealed severe hypercalcemia with elevated PTHrP and suppressed parathyroid hormone levels. Thoracoabdominal computed tomography revealed an 8-cm left renal mass, which was pathologically diagnosed as a sarcomatoid RCC. She underwent left radical nephrectomy, after which serum calcium normalized and cognitive function improved markedly (Hasegawa Dementia Scale-Revised score 7→28). Conclusion: This case demonstrates that an unexplained cognitive decline may be the first sign of PTHrP-producing RCC. Checking serum calcium levels is essential, and surgical removal of the tumor can reverse both metabolic and neurological symptoms.