Most Missed IM Question - Primary Hypothyroidism

primary hypothyroidism

Educational Objective:

Recognize the presentation of pituitary hyperplasia.

Key Point:

Pituitary hyperplasia may simulate a sellar tumor. Primary hypothyroidism can cause a sellar mass from overproduction of thyrotropin-releasing hormone. The hormonal profile will show a high TSH level and a low T3 and T4 value.

Explanation:

The patient’s hormonal profile is suggestive of primary hypothyroidism. Lack of production of T3 and T4 causes, by negative biofeedback, and increase of the thyrotropin-releasing hormone in turn causes hyperplasia of the hypophysis.

The patient does not have a pituitary tumor; rather, he has diffuse hyperplasia of the hypophysis as a consequence of thyrotropin-releasing hormone stimuli.

A TSH-producing adenoma is associated with high, not low free T3 and T4 levels.

A patient with a hypothalamic lesion will not have a sellar mass.

A nonsecreting adenoma may cause symptoms from compression and potentially secondary hypothyroidism, but, in such a case,,, the TSH level would be low, along with low T3 and T4 levels

References:

Neves CP, Massolt ET, Peeters RP, Neggers SJ, de Herder WW. Pituitary hyperplasia: an uncommon presentation of a common disease. Endocrinol Diabetes Metab Case Rep. 2015;2015:150056.

Passeri E, Tufano A, Locatelli M, Lania AG, Ambrosi B, Corbetta S. Large pituitary hyperplasia in severe primary hypothyroidism. J Clin Endocrinol Metab. 2011;96(1):22-23.