To investigate the serum levels of insulin-like growth factor-I (IGF-I) in patients with fibromyalgia (FM) compared to healthy controls and patients with other rheumatic diseases, and to explore possible etiologic mechanisms of low IGF-I levels in patients with FM.
Five hundred patients with FM and 152 controls (74 healthy blood donors, 26 myofascial pain patients and 52 patients with other rheumatic diseases) were studied. All had measurements of acid extracted serum IGF-I. A subset of 90 patients with FM were evaluated for clinical features that might explain low IGF-I levels. Twenty-five patients with FM underwent growth hormone (GH) provocation testing with l-dopa and clonidine.
The mean serum IGF-I level in patients with FM was 138 +/- 56 ng/ml and in controls 215 +/- 86 ng/ml (p = 0.00000000001). Low levels of IGF-I were not due to depression, tricyclic medications, nonsteroidal antiinflammatory drugs, poor aerobic conditioning, obesity, or pain level. Patients with focal myofascial pain syndromes had normal IGF-I levels (236 +/- 68), as did most patients with other rheumatic disorders, unless they had concomitant FM. Patients with FM with initially normal levels often had a rapid decline of IGF-I over 1 to 2 years. Most patients with FM with low IGF-I levels failed to secrete GH after stimulation with clonidine and l-dopa.
Many, but not all, patients with FM have low levels of IGF-I that cannot be explained by clinical associations. These results suggest that low IGF-I levels in patients with FM are a secondary phenomenon due to hypothalamic-pituitary-GH axis dysfunction.