Malignant hypercalcemia revealing a diffuse large B‐cell lymphoma in a patient with a previous diagnosis of chronic myelomonocytic leukemia: An uncommon hematological coexistence

Key Clinical Message A 76‐year‐old patient previously admitted to the cardiology department for replacement of a right ventricular lead on a double‐chamber pacemaker was admitted to the internal medicine department 15 days after for bronchopneumopathy. His past medical history was relevant for Type 2 diabetes mellitus, heart failure due to dilated hypokinetic heart disease, transcatheter aortic valve implantation (TAVI), and chronic myelomonocytic leukemia (CMML‐0) diagnosed in 2021. Twenty‐four hours after admission, the patient's general condition deteriorated abruptly, with the onset of drowsiness and psychomotor retardation. Laboratory exams revealed hypercalcemia at 4.18 mmol/L. Intensive hydration, calcitonin, and zoledronic acid were initiated and the patient was transferred to the nephrology intensive care unit where he underwent two sessions of hemodialysis to normalize serum calcium levels before readmission to internal medicine. Laboratory exams revealed low parathyroid hormone, normal 1‐25‐OH vitamin D, and increased parathyroid hormone‐related peptide. Thoracoabdominal and positron emission tomography (PET) scan showed diffuse abdominopelvic peritoneal carcinosis associated with low‐grade pleural effusion and multiple supra‐ and sub‐diaphragmatic adenopathies, leading to a search for a solid tumor. The patient's clinical condition worsened leading to a transfer to the intensive care unit. The biopsy of a peritoneal carcinosis nodule confirmed the diagnosis of diffuse large B‐cell lymphoma. Specific treatments were unsuccessful and the patient expired