The presence of hypercalcemia in hospitalized patients is usually a consequence of malignant tumors. Among these, multiple myeloma (MM) causes elevated calcium levels due to increased bone resorption mediated by cytokines, which stimulate osteoclast activity. Immobility and renal failure may also contribute. However, primary hyperparathyroidism (PHP) is the most common cause of hypercalcemia in outpatients. However, there are few reports on the association of HPP and MM. 

We present the case of a hospitalized woman diagnosed with multiple myeloma who, despite onco-specific treatment, persisted with elevated calcium levels. For this reason, a lesion association was sought, and primary hyperparathyroidism was diagnosed. Parathyroid scintigraphy identified a high uptake image, leading to surgical treatment. A parathyroidectomy was performed, and serum calcium levels normalized. The pathology report revealed hyperplasia. 

This case highlights the importance of a thorough etiological evaluation in patients with persistent severe hypercalcemia.