Prevalence of fibromyalgia in children: a clinical study of Mexican children.

Objective: To determine the prevalence of fibromyalgia (FM) in schoolchildren according to the 2 stage classification process proposed by the 1990 American College of Rheumatology (ACR) Multicenter Criteria Committee on Fibromyalgia.

Methods: Stage 1: we administered a pain questionnaire to a sample of 548 schoolchildren (264 boys, 284 girls; mean age 11.9 yrs, range 9-15). Stage 2: two rheumatologists examined all children with diffuse pain. Using thumb palpation, they examined 18 fibromyalgia tender points and 3 pairs of controls points followed by dolorimetry. Additionally, a random sample of 79 children with no pain were selected as controls, following the same procedures (thumb palpation and dolorimetry). The Wilcoxon test was used to compare the distribution of tenderness thresholds between FM and non-FM groups. Kappa statistics for multiple raters was used to assess interobserver agreement.

Results: Seven children, all girls, fulfilled the ACR diagnostic criteria for FM. Thus, the prevalence of FM in this group of schoolchildren reached only 1.2%. The girls with FM had a mean of 14 tender points, whereas controls (n = 79) had 2.4. Pain thresholds were 3.4 kg in children with FM and 5.1 kg in controls (p = 0.004).

Conclusions: The prevalence of FM in our study was 5-fold lower than a previous report. This variance may be due to (1) racial and sociocultural differences between populations; and (2) differences in methodological approach. The difficulties of making accurate estimates of FM across different studies are highlighted.