A LONGITUDINAL-STUDY OF CHANGES IN BODY-MASS INDEX AND TOTAL-BODY COMPOSITION AFTER RADIOIODINE TREATMENT FOR THYROTOXICOSIS

Patients treated for thyrotoxicosis often complain of increases in bod y weight after treatment of their thyroid disorder. The objective of t his study was to define the extent of changes in body mass and composi tion following treatment of thyrotoxicosis with radioiodine I-131. We prospectively measured body mass index (BMT) in 75 patients (18 males, 57 females), ranging in age from 15-88 years heated for thyrotoxicosi s with I-131 (doses ranging from 5.2 to 25.7 mCi) between 1978 and 199 4. BMT pre- and post-radioiodine treatment were recorded for up to 10 years after treatment. Body composition studies were performed on a su bgroup of 9 patients (1 male, 8 females), aged 24 to 74 years treated with 6.0 to 12.2 mCi I-131. Bone mineral content, lean mass, and fat c ontent were determined prior to and following I-131 treatment through whole body scanning with a Hologic QDR-1000/W(R) dual energy x-ray den sitometer. Sustained increases in BMI averaging 2.33 kg/m(2) above bas eline (p<.01) were observed from the initial 6 months through the firs t 5 years after I-131 therapy. BMI was no different from pretreatment levels over the remainder of the 10-year follow-up period. Lean mass i ncreased significantly (p=.0004) by an average of 7.2 kg. Although bot h fat and mineral content appeared to increase, these changes were not statistically significant. Weight gain occurs within the first year a fter I-131 treatment of patients with thyrotoxicosis and is predominan tly due to increased lean mass (20.2%, p<.0005) although bone mineral content increased only marginally (4.62%, p=.10).