Prevalence of monoclonal gammopathy in patients with primary hyperparathyroidism: a prospective study.

The association between primary hyperparathyroidism (PHPT) and monoclonal gammopathy has been reported, but whether it is fortuitous remains unsettled. We conducted a prospective study to determine the prevalence of monoclonal gammopathies in patients with surgically proved PHPT. In 101 consecutive patients with PHPT, serum immunoglobulins were systematically studied using agarose gel electrophoresis and immunofixation before and, when appropriate, after parathyroid surgery. The PHPT population was compared with a control series of patients with other diseases requiring surgery and with a group of patients with benign disease of the thyroid gland matched for age and sex to the PHPT population. Monoclonal immunoglobulin was detected in 10 (10%) of 101 patients with PHPT (including 2 with multiple myeloma) compared with 2 (2%) of 127 patients who underwent other surgery (P =.005) and 3 (3%) of 101 patients with benign thyroid diseases (P =.04). The prevalence of monoclonal gammopathies is high in patients with PHPT. At minimum, sensitive serum protein electrophoresis should be performed routinely in all patients with PHPT. Conversely, in patients with monoclonal gammopathy who have hypercalcemia but no other symptoms of progressive disease, clinicians must seek PHPT.