The Prognostic Value of TSH Level at Diagnosis in Determining Early Therapeutic Success of Radioactive Iodine (131I) Treatment for Hyperthyroidism: A Prospective Follow-up Study

• Areas of Interest:

  • Other

  • Thyroid

Background: The 131I therapy outcome is confirmed after 6 months from 131I treatment while some suggest at 3 months. Thus, the treatment outcome could be affected by several factors, and it is a challenge in predicting the therapeutic outcome of 131I treatment. This study aimed to assess the prognostic value of TSH level at the diagnosis in determining the early therapeutic success among hyperthyroid patients receiving 10 mCi of 131I.

Methods: This study was performed at the Nuclear Medicine Unit at Peradeniya for 89 patients (67 GD and 22 TMNG) who were followed-up at 3 and 6 months after fixed-dose of 10 mCi 131I treatment. The outcome of 131I treatment was assessed at 3 and 6 months. Therapeutic success was considered achieving euthyroid or hypothyroid status and therapeutic failure was considered if remain hyperthyroidism.

Results: A success rate of 75.3% (n = 67) was noted at 6 months among the study population. But 49 patients (55.1%) had permanent therapeutic outcomes at the end of 3 months and 40 patients (44.9%) had at 6months. Patients who had therapeutic outcomes at 3 months had higher mean TSH (0.109 ± 0 .248 mU/L) compared with patients with outcomes at 06 months (0.027 ± 0.050 mU/L; p = 0.033). Linear regression showed a significant relationship between early outcome and diagnostic TSH level (standardized coefficient β = –0.216, p = 0.048). A therapeutic success among 41.6% (n = 37) at 3 months and among 33.7% (n = 30) at 6 months was noted. Therapeutic success at 3 months had a higher mean TSH (0.138 ± 0.284 mU/L) compared with therapeutic success at 6 months (0.027 ± 0.054 mU/L; p = 0.033). Similarly, early development of therapeutic success and the TSH level at diagnosis showed a significant relationship (standardized coefficient β = –0.253, p = 0.047). But this relationship (standardized coefficient β = –0.155, p = 0.878) and the difference in TSH level wasn’t noted among patients who had therapeutic failure at early (0.028 ± 0.043 mU/L) or later (0.026 ± 0.039 mU/L; p = 0.878).

Conclusion: The TSH level at the time of diagnosis of hyperthyroidism shows an inverse relationship with the time required to reach the definitive outcome after 131I treatment.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
10 May 2022