Postpartum thyrotoxicosis in a patient with Graves' disease. Association with low radioactive iodine uptake.

A patient with previously diagnosed Graves' hyperthyroidism had a transient episode of thyrotoxicosis three months postpartum. This was associated with a diffusely enlarged thyroid gland, a rise in antithyroid microsomal antibody titer, a 24-hour radioactive iodine uptake (RAIU) of 1%, and an aspiration biopsy specimen suggestive of chronic lymphocytic thyroiditis. An alternative cause for the depressed RAIU was not discovered. This case would suggest that patients with previously diagnosed Graves' disease can have thyrotoxicosis without an enhanced RAIU and that the postpartum thyrotoxic syndrome may involve an immunologic injury causing a release of performed thyroid hormone.