Endocrine Abstracts

TSH secreting tumours (TSH-omas) are uncommon, accounting for less than 2% of pituitary tumours. Typically, patients with such tumours demonstrate hyperthyroidism with detectable or elevated TSH levels, and show little response to TRH stimulation. Treatment is controversial: typically surgery, radiotherapy or somatostatin analogues.

We present a 22 year-old man who was found to be tachycardic on joining a gym in 2003. There were no other symptoms or signs of thyrotoxicosis and no family history. Thyroid function tests revealed FT₃: 22.0 pmol/l (3.8–6.0 pmol/l), FT₄: 41.1 pmol/l (8–21 pmol/l) and TSH: 3.41 mIU/l (0.35–3.5 mIU/l), anti-TPO antibodies negative. Non-dynamic pituitary MRI was normal. Anterior pituitary function was otherwise normal and a recent TRH stimulation (2008) showed slight incremental response of TSH. Alpha-subunit was normal at 0.35 iu/l (<1.0 iu/l).

The diagnoses of resistance to thyroid hormones (RTH) or familial dysalbuminaemic hyperthyroxinaemia (FDH) were considered and excluded by genetic analysis of the thyroid hormone receptor and albumin genes. Dynamic MRI was then performed and demonstrated a 6 mm poorly enhancing nodule within the right half of the pituitary gland. A diagnosis of TSHoma was therefore tentatively made, and he was treated with beta-blockers, pending a decision on surgery.

However, the patient elected to stop all treatment in 2005. He remains asymptomatic, clinically and biochemically euthyroid, and eupituitary under regular review. Latest TRH tests continue to show a flat TSH response and repeat dynamic MRI in 2008 continues to demonstrate a poorly enhancing right pituitary gland, suspicious but not diagnostic of a pituitary microadenoma.

This represents the first recorded case of a spontaneously resolving TSHoma.

Annual TFT’s are illustrated below: