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Letters to the Editor |
University of California, Davis School of Medicine Sacramento, California 95817
In the previous letter, Karlsson et al. raise several issues. Although determination of remission rate was not a primary aim of our study, they question whether the remission rate for pediatric hyperthyroidism is truly 25% with every 2 yr of medical therapy. They cite concerns regarding lack of long-term follow-up. In our study (1), we defined remission as maintenance of normal serum T4 or fT4 concentrations without medication for greater than 6 months. Because our study was retrospective in design, long-term follow-up was not available for many patients. Use of a definition of remission that required follow-up periods longer than 6 months in a retrospective study would have resulted in excessive restriction of the sample size. Because determination of the remission rate was not the primary objective of our study, we felt justified in using this definition. We acknowledge that our definition of remission may have resulted in some patients being misclassified, and this was clearly stated in the limitation section of the article. While we cannot exclude the possibility of selection bias in determining which patients continued medical treatment, of the 85 patients who were excluded, 35 (41%) were lost to follow-up, 7 (8%) preferred initial treatment with surgery or radioablation, 10 (12%) were non-compliant, 9 (11%) had complications of medical therapy, 12 (14%) opted to discontinue medical therapy because of dissatisfaction with frequent office visits and blood testing, and 3 (4%) chose surgical therapy for cosmetic reasons. Only 9 (11%) continued to have elevated T4 and/or T3 concentrations at the time of surgery or radioablation and thus could possibly be said to have failed medical therapy. Of these 9 patients, however, noncompliance was suspected in 5. Thus, there is no clear indication that the exclusion of these 85 patients would have been likely to bias the results of the study.
Despite the limitations of our study as described above, we do not feel that the stated remission rate of 25% with every 2 yr of treatment is markedly inaccurate. The remission rate observed in our study agrees with that observed by Lippe et al. (2) and Collen et al. (3) in their previous prospective studies. In the initial study by Collen et al., the authors followed a cohort of 65 pediatric patients with hyperthyroidism for periods ranging from 3 months to 16 yr. They used life-table analysis methods to determine the distribution of remission times in the population. In that study, the authors defined remission as maintenance of clinical and biochemical euthyroidism for at least 1 yr without antithyroid medication. They determined that approximately 25% of patients achieve remission with every 2 yr of treatment. In a second study by Lippe et al., the same group followed the cohort of patients from the first study for an additional 5 yr. Even with this additional follow-up period, the remission rate remained the same. The authors note that only one of 36 patients who achieved remission experienced a relapse after remaining euthyroid for greater than 1 yr without antithyroid medication. The remaining 35 patients had been followed for a mean of 3.3 ± 2.9 yr (range 1–11.7 yr) without experiencing a relapse. Both the relatively long follow-up period in these studies as well as the concordance of the remission rate observed in these studies with that observed in our study argues strongly that the figure is likely an accurate one.
Karlsson et al. (4) state that, in their study of 31 pediatric patients with hyperthyroidism, only 19% entered remission after a median of 6.5 yr of medical therapy. The authors, however, do not report data regarding predictive variables such as goiter size and body mass, index which were determined in our study to influence the likelihood of early remission. In addition, the sample size for their study was small. Finally, 21% of the patients in their study were treated with antithyroid medication for 2 yr or less before surgery and 67% were treated for 4 yr or less. We feel that determination of accurate remission rates from this small study group, many of whom were treated for relatively brief periods, is difficult.
Karlsson et al. favor the use of surgery after a brief attempt at medical management. While the optimal treatment for pediatric hyperthyroidism continues to be controversial, we feel that their strategy would subject many children to unnecessary surgical procedures and the risk of surgical complications. We continue to advocate medical therapy as the first line of treatment, particularly in patients who present with small goiters and body mass index SD scores greater than -0.5 SD, indicative of a high likelihood of achieving remission within 2 yr.
As concerns the issue of increased risk of autoimmune thyroid disease in children with Down’s syndrome, this is a well-established fact. Children with Down’s syndrome constituted 3% of our study population. This information (along with information regarding other concurrent medical disorders in the study population) was not included in the manuscript merely because of the desire to keep the manuscript concise. Children with Down’s syndrome were not excluded from the analysis, and the care of children with Down’s syndrome in our clinics certainly is no different from that of other children.
Footnotes
Address correspondence to: Nicole S. Glaser, M.D., Department of Pediatric Endocrinology, University of California, Davis, 2516 Stockholm Boulevard, Room 339, Ticon II, Sacramento, California 95817.
Received January 9, 1998.
References
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