ABSTRACT 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.
Yano et al. (Thu,) studied this question.