Furthermore, data analysis showed that the average period of the disease was similar among patients with normal and abnormal amplitudes. However, it was significantly higher in patients with the following findings: abnormal amplitude of the sural and sensory median, increased latency of   the motormedian, ulnar, tibial and peroneal nerves, and raised latency of the sensory median nerves. The average duration of disease in patients with abnormal velocity of the all nerves was significantly more than those with normal velocity, except for the sural, the sensory ulnar and the motor tibial nerves (Table 4).

Discussion

The most common abnormality in this study was found in the NCV of the sural nerves (30%), followed by the tibial nerves (27.5%). The reported abnormalities of the peripheral nerves are various in the previous studies. For example, NCV abnormalities were reported in 29.4% of MS patients by Gartzenk et al. [7] and in only 5% by Misawa et al. [3]. In Shefner's study, 9 patients out of 14 showed normal amplitude and velocity [8]. In Pogonzelski's study, 74% of sufferers had at least one abnormality of the electrodiagnostic parameters that was not shown to be related to age, sex, and duration of the disease [5], while in our study some of the electrodiagnostic disturbances were seen in younger ages. In Ayromlu's study, abnormal amplitude (22.5%) and velocity of the motor nerves (33%) were common, while the frequency of abnormal velocity of the sensory nerves was not more common compared with the normal population [9].

In a study conducted by Anlar et al. the most common electrodiagnostic abnormality was low amplitude of ulnar and sural nerves that were detected in 16.5% of MS patients. Again, this research did not show any relationship between peripheral nerve disorders and MS signs, neurologic deficits and gender [10]. In contrast, the present study showed that abnormal amplitude  of some of the peripheral nerves was seen more in male patients, while velocity and latency disturbances did not differ with gender. Besides, it was observed that the longer duration of MS disease, the higher the frequency of some abnormal findings, specially delayed latencies of all motor nerves and the sensory median nerve.

On the other hand, the amplitude disturbances in our study, did not accompany a higher number of MRI plaques. Also, the EDSS scores were not related to electrodiagnostic parameters. Hence, we did not find an association between peripheral nerve affection and disability related to MS. Sarova-Pinhas et al. also showed no relationship between NCS findings and disability among MS patients [11], to best of our knowledge, the present study is the only one that analyzed the correlation between MRI plaques and NCS abnormalities.

Altogether, peripheral nerve involvements have been reported to be between 5 to 74 percent in MS patients [3,5,7,9,10]. This wide range of frequency may be attributed to genetic diversity or different sample sizes and inclusion/exclusion criteria. In the other Iranian study (Ayromlu et al.), the frequency of abnormalities was near to our study [9], which may be explained by genetic factors or common    environmental   agents  that  affect both peripheral and central nervous system. These findings may support some aspect of currently proposed pathophysiology of MS disease. On the other hand, based on the aim of the studies, the results are different. For instance, the lowest figure (5%) represented only significant demyelinating polyneuropathy reported by Misawa et al. [3], while the highest figure (74%) belonged to the Pogonzelski's study, showed any subclinical lesions of the peripheral nervous system in MS [5]. Also, sample size may justify the different results. Anlar et al.’ study with 20 subjects reported 16.5% abnormalities, while Gartzen et al. study with a sample size similar to our study (54 subjects) found 29.6% abnormal findings [7].

 In general, it seems that younger patients suffering from MS for longer periods of time are more susceptible to develop some peripheral nerve disorders, especially for delayed latencies of the motor ulnar and tibial, and the sensory median nerves. In addition, the presence of peripheral nerve abnormalities in some MS patients may open a window to understanding the nature of the demyelinating process in this disease.

Conclusion

This study showed that abnormalities of the peripheral nerve system occurred regardless of MRI plaques or EDSS. On the other hand, disease duration, age and gender were associated with some peripheral nerve abnormalities. 

Acknowledgments

 The authors appreciate the cooperation of electrodignostic staff in Qaem hospital and the neurology department of Mashhad University of Medical Sciences.

Conflict of Interest

The authors have no conflict of interest. 

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