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Frederick Vogel, Leah Braun, German Rubinstein, Stephanie Zopp, Sarina Benedix, Holger Schneider, Katrin Ritzel, Katharina Schilbach, Ralf Schmidmaier, Felix Beuschlein, Martin Bidlingmaier, and Martin Reincke

Background

Glucocorticoid excess leads to muscle atrophy and weakness in patients with endogenous Cushing’s syndrome. Insulin-like growth factor I (IGF-I) is known to have protective effects on muscle loss. We hypothesized that individual serum IGF-I concentrations might be predictive for long-term myopathy outcome in Cushing’s syndrome.

Patients and methods

In a prospective longitudinal study of 31 patients with florid Cushing’s syndrome, we analyzed IGF-I and IGF binding protein 3 (IGFBP 3) concentrations at the time of diagnosis and following surgical remission over a period of up to 3 years. We assessed muscle strength by grip strength measurements using a hand grip dynamometer and muscle mass by bio-impedance measurements.

Findings

Individual serum IGF-I concentrations in the postoperative phase were strongly predictive of long-term grip strength outcome (rs = 0.696, P ≤ 0.001). Also, lower IGF-I concentrations were associated with a lower muscle mass after 3 years (rs = 0.404, P  = 0.033). While patients with high IGF-I s.d. scores (SDS; >1.4) showed an improvement in grip strength within the follow-up period (P  = 0.009), patients with lower IGF-I SDS (≤−0.4) had a worse outcome with persisting muscle dysfunction. In contrast, preoperative IGF-I concentrations during the florid phase of Cushing’s syndrome did not predict long-term muscle function outcome (rs = 0.285, P  = 0.127).

Conclusion

Lower individual IGF-I concentrations 6 months after curative surgery for Cushing’s syndrome are associated with adverse long-term myopathy outcome and IGF-I might be essential for muscle regeneration in the early phase after correction of hypercortisolism.