Primary hyperparathyroidism and monoclonal gammopathy of undetermined significance.

Association of monoclonal gammopathies of undetermined significance with primary hyperparathyroidism has been reported by several investigators. We reviewed the records of our cases of surgically proven parathyroid adenoma with serum protein electrophoresis within 6 months preceding parathyroidectomy. Among 911 patients who had hyperparathyroidism and were more than 50 years old, immunoelectrophoresis revealed a monoclonal gammopathy of undetermined significance in nine (1.0%). This incidence is similar to those in two studies of a normal population (1.25% and 1.6%). In our nine patients, the monoclonal proteins ranged from 1.0 to 1.9 g/dl. The monoclonal protein was unchanged during follow-up (median 62 months) in eight and increased in one (who probably has evolving multiple myeloma). Nine of the 911 patients with hyperparathyroidism had a malignancy, and this also is similar to previously reported experience.