Serum insulin-like growth factor-I (IGF-I) does not correlate positively with isometric strength, fatigue, and quality of life in post-polio syndrome

Objectives and background: To determine if serum insulin-like growth factor -I (IGF-I) levels are associated with strength, body mass index (BMI), fati gue, or quality of life in post-poliomyelitis syndrome (PPS). PPS is Likely due to a distal disintegration of enlarged post-polio motor units as a res ult of terminal axonal sprouting. Age-related decline in growth hormone and IGF-I (which support terminal axonal sprouts) is proposed as a contributin g factor. Methods: As part of the North American Post-Poliomyelitis Pyridos tigmine Study (NAPPS), baseline data on maximum voluntary isometric contrac tion (MVIC), BMI, subjective fatigue (fatigue severity scale, Hare fatigue symptom scale), health-related quality of Life (short form health survey-36 ; SF-36), and serum IGF-I levels were gathered on 112 PPS patients. Pearson correlation coefficients were calculated to evaluate the association betwe en serum IGF-I and MVIC in 12 muscles, BMI, two fatigue scales, and SF-36 s cale scores. Results: There is a significant inverse correlation of IGF-I l evels with MVIC in left ankle dorsiflexors (r=-0.30, P<0.01), and left and right knee extensors (r=-0.22, -0.25, P=<0.01, 0.01), but no significant co rrelations in other muscles. When men and women were evaluated separately, inverse correlations of IGF-I levels with MVIC were found only in men. IGF- I correlated inversely with BMI (r=-0.32, P=0006) and age (r=-0.32, P=0.000 5). IGF-I did not correlate with the fatigue or SF-36 scales. Conclusions: In this exploratory study, we found that contrary to our expectations, IGF- I did not correlate positively with strength. IGF-I correlated negatively w ith strength in several lower extremity muscles, BMI, and age. IGF-I is lik ely not an important factor in the pathogenesis of fatigue and in determini ng quality of life in PPS, but its role on strength should be studied furth er. (C) 2001 Elsevier Science BN. All rights reserved.