Low levels of somatomedin C in patients with the fibromyalgia syndrome. A possible link between sleep and muscle pain

Objective. Fibromyalgia is a common syndrome of musculoskeletal pain and fatigue. Lacking distinctive tissue or laboratory correlations, it has often been considered a form of “psychogenic rheumatism.” In the present study, the notion that the stage‐4 sleep anomaly typically seen in the fibromyalgia syndrome may disrupt growth hormone secretion was tested. Because growth hormone has a very short half‐life, serum levels of somatomedin C were measured; somatomedin C is the major mediator of growth hormone's anabolic actions and is a prerequisite for normal muscle homeostasis. Methods. Serum levels of somatomedin C were measured in 70 female fibromyalgia patients and 55 healthy controls, using a peptide‐specific radioimmunoassay. Results. Significantly lower levels of somatomedin C were observed in the fibromyalgia patients compared with controls (mean ± SD 124.7 ± 47 ng/ml versus 175.2 ± 60 ng/ml; P = 0.000001). These results could not be explained by concomitant therapy or by weight, and in a subset of 21 patients in whom this was investigated, there was no correlation with various indices of disease activity. Conclusion. These findings indicate that there is a distinctive disruption of the growth hormone‐somatomedin C neuroendocrine axis in a majority of fibromyalgia patients. It is hypothesized that this abnormality may explain the link between disturbed sleep and predisposition to muscle pain.