Endocrine Abstracts

A 54yr old female presented with a 12-month history of tremor, sweating, anxiety and occasional palpitations. There was no past medical or family history of note. On examination, she had a fine tremor but no neck masses or eye signs. Her FT4 20.8 pmol/l (8pmol/l-22pmol/l), FT3 7.3 pmol/l (3.5-6.5pmol/l) with a suppressed TSH less than 0.01mu/l (0.35mu/l-5.5mu/l); 99Tc scan showed an autonomous hot nodule in the right lower lobe of the thyroid with partial suppression of the remainder of the gland. Serum thyroglobulin and microsomal antibody titres were negative . Her symptoms persisted with a FT4 of 23.0 pmol/l, T3 of 6.5 pmol/l and TSH < 0.01mu/l.

She was treated with 600mbq of 131I. Her FT4 fell to 19.7pmol/l, FT3 to 5.5pmol/l, but TSH remained suppressed several months later. Her symptoms continued; free thyroid hormone concentrations were normal, but TSH remained suppressed. Thyroid ultrasound showed a

5 mm cyst in the right lower lobe with flecks of calcification.

A repeat technetium scan showed partially reduced uptake in the inferior aspect of the right lower lobe with recovery of tracer uptake elsewhere. Her TSH receptor stimulating antibodies were positive(59% inhibition of TSH binding) . FT4 20.2pmol/l(8pmol/l-22pmol/l), FT3 7.8pmol/l(3.5pmol/l-7pmol/l) and TSH less than 0.01mu/l(0.35mu/l-5.5mu/l). She elected to undergo a subtotal thyroidectomy; histology of the gland is awaited.

Our patient initially appeared to have had mild T3-toxicosis due to a single hot nodule. Following radioiodine treatment her TSH remained suppressed and her symptoms persisted. Repeat imaging showed successful treatment of the hot nodule. The continued suppression of TSH appeared to be attributable to TSH receptor antibodies stimulating the remainder of the gland. Thus, successful radioactive iodine treatment for a hot nodule appeared to unmasked underlying Graves' disease in our patient.