Pituitary hyperplasia secondary to primary hypothyroidism: a case report and review of the literature.

Pituitary hyperplasia secondary to primary hypothyroidism has been reported in the literature in both adults and children. We report a case of a young woman who was diagnosed with hypothyroidism in her teenage years. Despite frequent follow-up, her TSH levels remained greater than 100 mIU/ml. A few years later, pituitary enlargement was found on an MRI at a time when her TSH was 177 mIU/ml and her free T4 was 0.2 ng/dl. Observed administration of 600 mcg of L-thyroxine was performed to determine the effectiveness of hormone absorption. Total T4 levels of 0.2 rose to 7.1 mcg/dl at two hours with a decrease in her TSH levels from 88.6 to 66.8 mIU/ml at 24 hours. With the exception of one short period, her TSH levels have remained elevated over eight years of observation without change in the size of the pituitary mass. In our review of the literature, primary uncontrolled hypothyroidism has been described as a precursor to pituitary hyperplasia. In these patients, TSH-secreting adenomas were distinguished from pituitary hyperplasia by a blunted TRH stimulation test, elevated alpha subunit concentration values, and elevated alpha subunit concentration/TSH ratios. TSH levels ranged from 98 to 732 mIU/ml in adults, and even higher values in children. Following adequate hormone replacement with L-thyroxine doses of 25 to 300 mcg/day, both symptoms and pituitary hyperplasia regressed on average within a few months.