ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 15 P377

TSH-secreting pituitary adenoma (TSH-oma) with coexistent autoimmune hypothyroidism

Srinivasa Rangan, Muhammad Karamat, Rosalind Mitchell, Neil Gittoes & Jayne Franklyn

University Hospital, Birmingham, UK.

A 69-year-old man with no family history of thyroid disease presented with weight gain and constipation. He was clinically euthyroid with no goitre. Investigations confirmed autoimmune hypothyroidism with FT4 16.9 pmol/l (N: 10–22), TSH 29.14 mIU/l (N: 0.4–4.5), elevated thyroid peroxidase (TPO) antibodies 3311 IU/ml (N: 0–34) and he was commenced on thyroxine with serial dose adjustments to 250 mcg OD over 2 years. His TSH however remained persistently elevated despite apparent good compliance. TFTs upon referral showed elevated FT4 27.5 pmol/l and TSH 15.7 mIU/l. Tests for heterophilic antibodies to T4, T3 and TSH were negative. A TRH test was neither suggestive of thyroid hormone resistance nor of TSH-oma. Repeat TFTs showed FT4 12.5 pmol/l and TSH 55.6 mIU/l and he was restarted on a trial of thyroxine 50 mcg OD. A year later, he presented with heat intolerance and sweating. Investigations confirmed secondary hypogonadism with low testosterone 6.2 nmol/l (N: 9–28), FSH 2.8 IU/l, LH 1.5 IU/l. TFTs showed FT4 25.6 pmol/l, TSH 18.66 mIU/l with elevated α-subunit at 4.85 IU/l (N: <1.00). Prolactin was 423 mu/l (85–325), IgF-1 15 nmol/l (8.9–32) and there was a normal synacthen response with a 30-min peak cortisol 712 nmol/l (N: >550 nmol/l). MRI pituitary showed a 1.7×1.5 cm pituitary tumour abutting the optic chiasm. Visual fields were normal on formal assessment. He was commenced on testosterone replacement and continued thyroxine 100 mcg OD. It was felt likely he had a TSH-oma on a background of autoimmune thyroid disease. Octreotide challenge with 100 mcg TDS demonstrated a reduction in TSH, improving from baseline 19.43 to 0.66 mIU/l at day 21 adding weight to the diagnosis of TSH-oma. He was switched to Somatulin Autogel 60 mg once monthly. Repeat MRI pituitary after 9 months showed evidence of tumour shrinkage with normalising TFT’s (FT4 14.8 pmol/l, TSH 4.9 mIU/l).

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