Background and case: A 38-year-old man presented acutely with left-sided retro-orbital pain, a heavy/numb sensation in his left arm and blurred vision and diplopia on left lateral gaze. Baseline biochemistry, liver function and haematology were normal. His TSH was 3.9 (0.34 mU/l) and CRP 92 mg/l (<10). Plain CT head was unremarkable as was the MRI as reported, and atypical migraine was suspected. Vertical diplopia on left lateral gaze and left upper arm paraesthesia persisted, however, and 4 months later, following repeat normal baseline bloods and normal CSF examination, a repeat MRI head demonstrated a 12×12 mm pituitary adenoma that was unchanged but had been overlooked on initial MRI.
Endocrine review: He was phenotypically normal with full visual fields. The only additional history was of anger and mood disturbance. Baseline pituitary function revealed a TSH of 4.5 mU/l with a FT4 of 28.5 pmol/l (1024) and FT3 of 7.6 pmol/l (2.87.1). Random PRL was 198 mIU/l (< 700), testosterone 20.6 nmol/l (1035) and GH 0.1 μg/l.
Management: Almost one year after his initial presentation and following 4 weeks of pre-operative preparation with carbimazole (15 mg/day), a transsphenoidal microadenomectomy for thyrotrophinoma was carried out. Post-operative FT4 and FT3 were 20.8 and 5.8 pmol/l respectively, with a TSH of 2.4 mIU/l. Immunohistochemistry showed predominantly GH immunostaining, with weak, scattered TSH positivity.
Discussion: The involvement of the left trochlear nerve is difficult to explain unless some degree of vascular shunting is adduced. The thyrotrophinoma did not encroach into the cavernous sinuses, however, and such a mechanism could certainly not explain the left arm symptoms. This case is a reminder that pituitary pathology which is generally straightforward to exclude, should be considered in the differential diagnoses of atypical headache, and that pituitary adenomas may cause very unusual neurological symptoms.