Endocrine Abstracts

Introduction: Pituitary tumorous hyperplasia with hyperprolactinemia has been described as a rare presentation of primary hypothyroidism. The loss of thyroxin feedback inhibition in primary hypothyroidism causes overproduction of thyrotropin-releasing-hormone (TRH), which results in secondary pituitary enlargement. TRH has a weak stimulatory effect on the lactotroph cells of the pituitary, so a mild to moderate increase in prolactin (PRL) levels is expected. This report describes an unusual case of primary hypothyroidism with pituitary hyperplasia mimicking a pituitary adenoma.

Case report: A 27 year old female patient admitted to the gynecology clinic with the complaint of infertility. A pituitary macroadenoma and mild hyperprolactinemia were detected after laboratory and radiological assessment and patient was referred to Endocrinology outpatient clinic. She had regular menstrual cycles and no galactorrhea. There were also no neurological symptoms such as headaches and visual disturbances. The patient had no known chronic disease and was not using any medication. Her hormonal profile showed raised thyrotrophin stimulating hormone (TSH) (44 μIU/ml, range 0.40–4.5) and low free T4 (0.78 ng/dl, range 0.88–1.72) and mildly elevated PRL levels (39.4 ng/ml, range: 5–25). The growth hormone and pituitary-adrenal axis were interpreted as normal. Magnetic resonance imaging (MRI) of pituitary showed 10×15 mm globular pituitary enlargement with a convex superior margin. Anti-thyroglobulin antibodies (>1300 IU/ml, range: 0–157) is found elevated while antimicrosomal antibodies was negative. Thyroid gland had a heterogeneous echotexture on the ultrasonography. A diagnosis of autoimmune thyroiditis and primary hypothyroidism with pituitary hyperplasia was suspected. Oral levothyroxine substitution treatment was started and the dose was increased gradually until euthyroidism was restored. After 6 months of follow-up, TSH and PRL levels dropped to their normal ranges and the pituitary enlargement was found regressed on MRI.

Conclusions: Pituitary enlargement secondary to primary hypothyroidism is known but uncommon entity and sometimes differentiation of pituitary gland enlargement from pituitary adenomas may be difficult. Interpretation of a pituitary mass without proper endocrine evaluation can lead to mismanagement and unnecessary treatment.