A 45-year-old woman presented for a routine review 8 weeks following her failed therapy with IFN-alpha2beta for her chronic HCV. She had been generally well with no significant previous medical history although there was a strong family history of thyroid disease in her family, with both her mother and grandmother experiencing thyroid diseases of undetermined nature, culminating in both requiring thyroxine supplement. Treatment for her HCV infection (genotype 1) was to be 48 weeks of RBV and IFN-alpha2beta. However, after 24 weeks, there was no reduction in viral load and treatment was terminated. Her monthly thyroid function tests had been normal till then. System review on this occasion did not reveal any symptoms to suggest thyroid disease. Clinical examination at the review visit showed no signs of hypothyroidism. Her vital signs were satisfactory, with normal tendon reflexes and no goitre. Her routine TSH was found to be 48.0 IU/L with undetectable fT4 level. The follow-up thyroid ultrasound revealed the presence of a small atrophic gland with total volume of 6 mls (RR, 6-10). Her anti-Tg and anti-TPO titres were 1 : 256 and 1 : 512, respectively. The TSI and hTRAB were 11 IU/L and 11.7 IU/L respectively. Her thyroid uptake study was low at 3%. A diagnosis of autoimmune hypothyroidism was made and consequently, thyroxine was started. She was stabilised on 100 mug of thyroxine daily. At six month review, her anti-Tg, anti-TPO, TSI and hTRAB antibodies were undetectable. In retrospect, the combination of high TSI and hTRAB titres with hypothyroidism and a low pertechnetate uptake study was consistent with the presence of thyrotropin blocking antibodies (TB-Ab). Based on this probable underlying mechanism for the hypothyroidism, thyroxine was ceased. The patient remained well and independent of thyroxine supplement in the following 12 months. Interferon-induced thyroiditis (in the hypothyroid phase) was unlikely given that there was no hyperthyroid phase. Functional TB-Ab assay would have been definitive but unfortunately was not available. 
 The clinical profiles of the three cases are represented schematically in Figure 1.