A 32-year-old lady was referred to our centre with thyrotoxicosis and elevated FT4 and TSH levels. She was already on carbimazole. Interestingly, her symptoms started at childhood. She was nicknamed shaky by her school friends because of her tremors. There was no family history of thyroid disease.
She was clinically and biochemically thyrotoxic with FT4 of 12.438.8 pmol/l and TSH of 7.2438.8 mIU/l.
After excluding assay interference as a possibility, Investigations revealed a normal α-subunit/TSH molar ratio, an appropriate rise in TSH during TRH test and no evidence of a pituitary adenoma on MRI. This suggested a diagnosis of pituitary thyroid hormone resistance (PTHR). However, sequencing thyroid hormone receptor-β (THR-β) gene did not identify any abnormality.
Following a TSH day curve to assess response to cabergoline and octreotide, carbimazole was switched to cabergoline which only resulted in partial clinical and biochemical improvement. She underwent further assessment at Addenbrokes Hospital. Negative genetic testing raised doubts about initial diagnosis. Re-sequencing THR-β gene and repeat MRI scan again did not identify any abnormality. Also, measurement of BMR, sleeping heart rate, SHBG and BMD to assess peripheral thyroid hormone actions confirmed the initial diagnosis.
Her thyrotoxicosis improved after adding triiodo-thyroacetic acid (TRAIC) to her treatment regimen. However, following MHRA guidance, a routine echocardiogram revealed severe MR. Therefore, cabergoline was switched to quinagolide following a repeat TSH day curve.
She underwent successful cardiac surgery. Currently, she is clinically and biochemically euthyroid and in addition to nadolol is taking TRAIC 700 μg BD and quinagolide 150 mg daily.
This case that revealed symptoms of thyrotoxicosis since childhood (nickname shaky) highlights important learning points including: diagnostic approach to a patient with TSH-induced thyrotoxicosis, value of TSH day curve, use of TRIAC and the relationship between cabergoline and fibrotic valvular heart disease.