Myxoedema presenting with chiasmal compression: resolution after thyroxine replacement

A 60-year-old woman presented with deteriorating vision. A computed tomography (CT) scan showed pituitary enlargement with chiasmal compression. Serum prolactin levels were normal but assessment of thyroid function showed a serum thyroxine level of 25 nmol/l (normal range 76-160 nmol/l) and a thyroid-stimulating hormone (TSH) level of 60 mU/l (normal range 0.5-5.0 mU/l). After 8 weeks of thyroxine replacement therapy (0.05 mg daily increasing to 0.1 mg daily after 3 weeks) the visual defects had resolved, serum TSH had fallen to 0.7 mU/l, and the CT scan showed pronounced reduction in the size of the pituitary gland. Measurement of TSH as well as prolactin is essential in all patients with pituitary enlargement, to avoid unnecessary pituitary surgery.