Thyrotropin-secreting Pituitary Tumors

Abstract

TSH tumors are associated with both hypothyroid and hyperthyroid states. The proposed mechanism of thyrotroph secretion is illustrated in Figure 8. Pituitary enlargement in hypothyroidism is usually due to reactive hyperplasia and correlates with the degree of TSH elevation. Although this often translates to long-standing hypothyroidism and severe symptoms, this is not always the case. Patients may be asymptomatic or present with other endocrine syndromes. Children may have precocious puberty, and adults may have amenorrhea or decreased libido. One important message to remember is that whenever a patient has evidence of a pituitary tumor, a serum T4 and TSH level must be obtained. The dramatic reduction in pituitary size and resolution of endocrine dysfunction with thyroid hormone is gratifying. Thyrotropinomas producing thyrotoxicosis are autonomous tumors. Given their infrequent occurrence, one could question the cost effectiveness of ordering a serum TSH on all new patients with hyperthyroidism. Features that might favor the possibility of there being a tumor include male sex, headaches, visual impairment, and the absence of ophthalmopathy. Unfortunately, these are not reliable clinical features to suggest the presence of this disorder, and the diagnosis requires a serum TSH determination. Fortunately, the newer assays available are able to provide the sensitivity needed. Therapy should be aimed at the pituitary gland, but currently it is less than optimal. Surgery with or without external irradiation offers the best prognosis and, hopefully, will yield better results when cases are identified earlier. Medical therapy to suppress TSH is still in its infancy. More effective agents will hopefully be discovered in the near future.