OBJECTIVE: To examine the factors associated with persistence or recurrence of hyperthyroidism following an initial therapy dose of 131 I. METHODS: Retrospective case-note review of all patients with hyperthyroidism treated with a fixed dose of 400 MBq 131 I at a single reference centre (1992 to 1997). From the 104 patients treated during that period, six had a multinodular goitre and one, a toxic adenoma; 96 were taking thionamide preparations, which were discontinued 7 days prior to radioiodine administration. RESULTS: Early progression to hypothyroidism was observed at a median of 88 days (22-214) in 60 patients (57.7%). Persistence or early recurrence of hyperthyroidism was observed in 13 (12.5%) and was positively correlated with age (p<0.007), although unrelated to underlying diagnosis. There was a higher prevalence of persistent disease in those treated with propylthiouracil rather than carbimazol prior to radioiodine (35% vs. 8%; p<0.006). CONCLUSIONS: This study suggests that the blocking effect of thionamides on radioiodine uptake may be more prolonged in older people. It also suggests that the effect of propylthiouracil may last longer than that of carbimazol.
Iodine; Radioiodine; Hyperthyroidism; Graves; Recurrence