Endocrine Abstracts

Background: Pituitary adenomas commonly present with palsies involving the cranial nerves in the cavernous sinus. It is unusual, however, for other cranial nerve palsies to co-present and to have biochemical results that do not fit with the clinical picture.

Case: A 47 year old man was admitted with 3 days of headache, vomiting, right sided facial paraesthesia and facial droop. He had no symptoms suggestive of endocrine disturbance. Neurological examination revealed right lower motor neurone facial nerve palsy. Admission CT scan showed a pituitary macroadenoma and soft tissue in the right middle ear and mastoid air cells. Pituitary profile showed prolactin: 95570 miu/L, testosterone: 0.8 nmol/L, LH: 1 iu/L, FSH: 1.1 iu/L. Thyroid function showed fT4: 118.9 pmol/L and TSH: 3.2 miu/L. These suggested a macroprolactinoma with co-secretion of TSH leading to raised fT4. Dedicated pituitary and neck MRIs showed a 40 mm × 32 mm × 47 mm pituitary mass and soft tissue in the right middle ear and facial nerve canal, separate from the pituitary lesion. Formal visual testing revealed bitemporal hemianopia.

Cabergoline was started. No treatment for the high fT4 was started due to the absence of symptoms and simply re-testing using a different assay was arranged. These returned normal and repeat TFTs using our lab following discharge also returned normal, suggesting assay interference. With cabergoline, serum prolactin reduced significantly and his macroadenoma also shrunk. ENT advice was sought for the middle ear lesion and facial nerve palsy, and this was managed separately.

Discussion: It is thought that low molecular weight heparin caused assay interference through displacement of T4 from its binding site on proteins (e.g. thyroglobulin) during the assay whilst he was an inpatient. This leads to falsely raised fT4, normal TSH and a clinically euthyroid patient. It is therefore important to think of assay interference when investigations are discordant with clinical symptoms.