Endocrine Abstracts

Introduction: Thyrotroph pituitary hyperplasia in context of severe primary hypothyroidism is rare and usually occurs due to loss of thyroxine feedback inhibition and overproduction of thyrotropin-releasing hormone, leading to pituitary gland enlargement. Pituitary hyperplasia caused by primary hypothyroidism responds well to thyroid hormone replacement therapy and rarely requires surgical intervention.

Case presentation: A 42-year-old female with background history of type 2 diabetes, hypothyroidism, transient ischaemic attack (TIA) glaucoma and epilepsy presented initially with light-headedness. Systemic examination was unremarkable. Biochemical assessment revealed severe primary hypothyroidism with TSH of 442 milliunit/l (NR 0.30- 4.20 milliunit/l), free T4 5.2 pmol/l (NR 9-23 pmol/l) and mild hyperprolactinaemia. Magnetic resonance imaging (MRI) revealed a large pituitary macroadenoma with extension into the suprasellar compartment, without compression of the optic chiasm. The patient required escalating doses of levothyroxine, maximally 300 mg daily due to variable compliance (levothyroxine absorption test normal). Imaging was repeated when the patient’s TSH had fallen to 0.37 milliunit/l. The repeat MRI pituitary showed marked reduction in the size of the pituitary enlargement, making the diagnosis of thyrotroph pituitary hyperplasia.

Conclusion: Pituitary hyperplasia caused by primary hypothyroidism usually has a good response to thyroid hormone replacement therapy. Surgical intervention is not usually required.