Endocrine Abstracts

Pituitary hyperplasia secondary to primary hypothyroidism (PHPH) is a consequence of long term untreated or uncontrolled primary hypothyroidism. The proliferation of thyrotrophs in the pituitary gland, due to the lack of negative feedback on the hypothalamus from low circulating thyroid hormone levels, causes elevated thyroid stimulating hormone (TSH) levels. Hyperprolactinaemia can also be present due to the stimulatory effect of TSH on lactotrophs. Pituitary hyperplasia causes enlargement of the pituitary gland, and pituitary imaging with Magnetic Resonance Imaging (MRI) may not always reliably differentiate between pituitary adenoma and hyperplasia.

Case report: A 23-year-old lady, diagnosed with primary hypothyroidism at age 7. Thyroid function tests (TFTs) showed persistently elevated TSH levels. No hypothyroid symptoms reported other than irregular menses and constipation. No reported issues with compliance from patient. No history of glandular fever, coeliac screen was negative. Alpha subunit measurement was normal. Assay interference was excluded. Pituitary profile bloods were within range other than mild hyperprolactinaemia. Dynamic Pituitary MRI reported a bulky pituitary gland, measuring 16 x 11 x 13 mm, with convex upper border protruding into the suprasellar cistern. Regional Pituitary MDT discussion reported physiological hyperplasia, likely due to poorly controlled primary hypothyroidism. Further imaging following good adherence to treatment reported pituitary size reduction.

Conclusion: Pituitary hyperplasia in prolonged, poorly controlled hypothyroidism is a common finding. The importance of biochemical evaluation cannot be dismissed in favour of pituitary imaging; hyperplasia can be misdiagnosed as pituitary adenoma and where there is visual compromise due to hyperplasia, unnecessary surgery may be performed. Hyperplasia can be reversed with levothyroxine replacement and good adherence to replacement. Correct evaluation of patients with robust history taking and biochemical investigations lessens the possibility of patients undergoing unwarranted surgical interventions.