Autoimmune hypothyroidism coexisting with a pituitary adenoma secreting thyroid-stimulating hormone, prolactin and alpha-subunit

A 44-year-old woman presented to her GP with excessive tiredness. She had p ositive thyroid microsomal and thyroglobulin autoantibodies and was found t o have an elevated serum thyroid-stimulating hormone (TSH) concentration of 8.37 (normal =0.15-3.5) mU/L and a low normal total thyroxine (T-4) of 86 (reference range 60-145)nmol/L. She was rendered symptom free on a dose of 150 mug of thyroxine per day. However, her TSH failed to return to normal, and following a further increase in her thyroxine dose she was referred to the endocrine clinic for further assessment. Her TSH at this stage was 14mU /L, free T-4 (fT(4)) 28 (normal= 10-27)pmol/L and free T-3 (fT(3)) 10 (norm al=4.3-7.6)pmol/L. She denied any problems with adherence to her medication . Her serum prolactin was elevated at 861 (normal= 60-390)mU/L. A pituitary tumour was suspected and an MRI scan showed a macroadenoma of the right lo be of the pituitary, extending into the suprasellar cistern. The tumour was resected trans-sphenoidally. Electron microscopy showed a dual population of neoplastic cells compatible with a thyrotroph cell and prolactin-secreti ng adenoma. Immunocytochemistry and cell culture studies confirmed the secr etion of TSH, prolactin and a-subunit. Postoperative combined anterior pitu itary function tests did not demonstrate any deficiency of anterior pituita ry hormones. A repeat MRI scan showed no significant residual tumour; howev er, her serum TSH and prolactin levels remained high and she was given a co urse of pituitary irradiation. This case illustrates the difficulty of diag nosing a TSHoma when it coexists with autoimmune hypothyroidism. We believe the combination of pathologies reported here is unique.