Riedel's struma associated with subacute thyroiditis, hypothyroidism, and hypoparathyroidism.

Riedel's struma with dense fibrous invasion of surrounding muscle and fat was found in a patient who had clinical subacute thyroiditis superimposed on primary hypothyroidism. Riedel's struma may sometimes be an uncommon stage in the more common subacute form of thyroiditis, although in our patient an unusual coincidence of subacute thyroiditis and Riedel's struma is also possible. Of interest in our patient was the development of spontaneous primary hypoparathyroidism; parathyroid function returned to normal concomitant with the spontaneous resolution of the goiter after partial resection. This patient also represents another instance of hyperthyroidism developing in a previously hypothyroid patient.