WHEN NEW ONSET POLYURIA AND POLYDIPSIA DOES NOT EQUAL DIABETES. E.W. Vogel 1 ; 1 MCP Hahnemann University, Philadelphia, PA LEARNING OBJECTIVES: 1. Recognize severe hypercalcemia as a cause of polyuria and polydipsia, and check for hypercalcemia in patients with polyuria when diabetes has been ruled out. 2. Recognize parathyroid carcinoma as a cause of severe hypercalcemia. CASE INFORMATION: A 37 year old African American female with no significant past medical history presented with a two to three week history of increasing thirst, leading to intake of approximately three liters of water per day, associated with urination every 30 minutes. She also noted some polyphagia, dizziness, and mild blurred vision. She had a strong family history of type 2 diabetes, with her mother, brother, and uncle all having diabetes. On a brief initial physical examination, no significant abnormalities were detected. Somewhat surprisingly, her office finger stick glucose measurement was only 106 mg/dl. A basic sevenitem chemistry panel, urinalysis, and hemoglobin A1C were sent to the lab from the office, and the patient was released to home. Although not specifically ordered initially, a calcium level included with the chemistry panel came back at 14.5 mg/dl; her glucose and hemoglobin A1C were normal. The patient was admitted to the hospital for treatment, and on reexamination was found to have a hard left thyroid mass. Her parathyroid hormone level was markedly elevated at 485 pg/ml, with normal thyroid function tests. After resolution of her hypercalcemia with intravenous normal saline and pamidronate, she underwent surgical neck exploration, and was found to have a tumor extending from her thyroid to local skeletal muscle and the esophagus. Pathological examination revealed parathyroid carcinoma. The patient later was found to also have metastatic disease in her lungs. Despite primary tumor resection, local neck irradiation, chemotherapy, and multiple outpatient doses of pamidronate, the patient has required several admissions for management of recurrent, severe hypercalcemia. DISCUSSION: Severe hypercalcemia can have a number of clinical manifestations, including polyuria and polydipsia. Interestingly, this patient manifested none of the more common findings of hypercalcemia at the time of presentation, such as bone pain, renal colic from nephrolithiasis, or gastrointestinal or neurological symptoms. Clinicians should therefore consider hypercalcemia in the differential diagnosis of polyuria, especially when diabetes has been ruled out. In this case, the serum calcium was not ordered initially, but luckily this laboratory routinely includes a calcium level with the chemistry seven panel, which established the diagnosis. Parathyroid carcinoma is a rare cause of hypercalcemia; an underlying parathyroid cancer causes only 1 to 2 percent of cases of primary hyperparathyroidism. This patient had two of the warning signs for parathyroid carcinoma as the cause for primary hyperparathyroidism: severe hypercalcemia at the time of presentation ( > 14 mg/dl), and a palpable neck mass. This patient also typifies the clinical course of parathyroid carcinoma that is not cured by primary surgery, in that she has developed recurrent episodes of severe hypercalcemia. This persistent hypercalcemia eventually results in renal and cardiac complications, accounting for most of the morbidity and mortality associated with this disease.