Effect of age on the fractional anisotropy (FA) value of peripheral nerves and clinical significance of the age-corrected FA value for evaluating polyneuropathies.

Introduction: We investigated the correlation between age and the fractional anisotropy (FA) values of peripheral nerves in healthy adults and compared the age-corrected FA values of peripheral nerves in healthy subjects and patients with polyneuropathy.

Methods: The institutional review board approved this study and informed consent was obtained from all participants before entry into the study. We optimized diffusion tensor imaging using a 3-T magnetic resonance scanner and an extremity coil for scanning tibial nerves. The effect of age and sex on the FA values of tibial nerves in healthy volunteers was investigated and the age-corrected FA values of tibial nerves in healthy volunteers and patients with polyneuropathy were compared.

Results: The maximum FA values of the tibial nerves remained constant until age 45 (approximately 0.516); they subsequently decreased by 0.004/year in healthy volunteers. After removing the effect of age with an age-adjusted equation, the median maximum FA values in the volunteers and patients were 0.518 (range, 0.406-0.616) and 0.442 (range, 0.376-0.530), respectively. The age-corrected FA values were significantly lower in the patients than the healthy volunteers (p < 0.001). There was no significant gender-related difference in the maximum FA values of the tibial nerves (p = 0.416).

Conclusion: The age-corrected FA value of the peripheral nerves helps to differentiate between age-related peripheral nerve degeneration and polyneuropathies.