Serum growth hormone and insulin but not insulin-like growth factor-1 levels are elevated in patients with fibromyalgia syndrome

Standard radioimmunoassay (RIA) was employed to quantify basal serum growth hormone (GH), insulin-like growth factor-I (IGF-1), and insulin levels in 32 normoglycemic patients with clinically active fibromyalgia and in 29 normoglycemic control subjects. The GH concentration was significantly higher (P<0.001) in female fibromyalgia patients than age-matched, normal female subjects. In contrast, basal serum IGF-1 concentrations did not differ between these groups. A scatter plot generated from two-stage, least-squares analysis showed that serum GH lacked correlation with the serum IGF-1 concentrations of normal female subjects (P=0.73) and female fibromyalgia patients (P=0.19). In addition to the results from serum GH and IGF-1 RIA, we also found significantly higher fasting serum insulin levels (P=0.03) in male fibromyalgia patients and a trend toward elevated fasting serum insulin levels in the female fibromyalgia population (P=0.07), with the mean fasting level in the male fibromyalgia group (35.7 μU/ml^-1) exceeding the upper limit of normal serum insulin levels (i.e., 27 µU/ml^-1). Based on these results, basal serum GH and fasting serum insulin levels appear to be valuable surrogate markers in clinically active, normoglycemic fibromyalgia patients.