Objectives and background: To determine if serum insulin-like growth factor-I (IGF-I) levels are associated with strength, body mass index (BMI), fatigue, 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 result of terminal axonal sprouting. Age-related decline in growth hormone and IGF-I (which support terminal axonal sprouts) is proposed as a contributing factor. Methods: As part of the North American Post-Poliomyelitis Pyridostigmine Study (NAPPS), baseline data on maximum voluntary isometric contraction (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 between serum IGF-I and MVIC in 12 muscles, BMI, two fatigue scales, and SF-36 scale scores. Results: There is a significant inverse correlation of IGF-I levels 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 correlations 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 = 0.0005). 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 with strength in several lower extremity muscles, BMI, and age. IGF-I is likely not an important factor in the pathogenesis of fatigue and in determining quality of life in PPS, but its role on strength should be studied further.
Bibliographical noteFunding Information:
This study was funded by ICN Pharmaceuticals, Inc. We acknowledge the help and support for the study provided by Dr Colin Granger, Dr Anne Nickel, and Ms Peggy Boag from ICN Pharmaceuticals, Inc. Dr Trojan is a Clinical Research Scholar, and Dr Collet is a Research Scholar supported by the Fonds de la recherche en santé du Québec. We acknowledge the help and expertise of Ms Pat Andres in assessing the reliability and standardizing the isometric muscle strength assessments at participating centers. We appreciate the generosity of Amgen Inc., Thousand Oaks, CA, who permitted us to use the section on procedures and methods for quantitative tests for neuromuscular evaluations (isometric muscle strength tests), which is part of the ‘Procedure Manual for the Clinical Evaluation of BDNF in ALS’ (Procedure Manual for BDNF Protocol 930121B) for the project manual for this study.
Copyright 2019 Elsevier B.V., All rights reserved.
- Body mass index
- Insulin-like growth factor-I
- Quality of life