The usefulness of standardization of the nerve conduction study in the diagnosis and follow up of the demyelinating polyneuropathy

ABSTRACT

BACKGROUND: Nerve conduction study is an objective and quantitative diagnostic method for the diagnosis and follow-up study of polyneuropathy. Sometimes it is hard to interpret the nerve conduction study, because there are many segmental variables to test and uneven distribution of abnormalities in polyneuropathy. And there can be some interpersonal differences in the interpreting the results. It is obvious that one objective and quantitative value that represents the many segmental variables is helpful for the clinical interpretation and follow?up of polyneuropathy. METHODS: We evaluated 242 normal subjects and 71 patients with demyelinating polyneuropathy to find out a standardized representative value, distinguishing patients from normal subjects. The standardized representative value was made by combination of the some standardized segmental variables which showed marked differences between two groups. We evaluated the clinical usefulness of this value by comparing the sequential changes of this value with the clinical course. RESULTS: Statistically significant differences were present in each segmental value of the nerve conduction study between the groups of patients and normal persons. The diagnostic sensitivity of the segmental value was in range of 25.7%-81.8% in case of 2SD criteria. The diagnostic sensitivity of each functional standardized value - average of the segmental standardized values of same nature - was in range of 54.1%-89.9% in case of 2SD criteria. Using 3SD criteria the sensitivity was reduced to 20.9%-81.1%, more in sensory and mixed nerve than motor nerve. By combination of these functional standardized values, the diagnostic sensitivity could increase up to 79.1%-93.2% on 3SD criteria. CONCLUSION: The best combination which represents the NCV study is the average of the motor nerve terminal latency, the motor nerve conduction velocity, and the ratio of conduction block with 93.2% sensitivity and 100% specificity. This representative value well reflects the clinical course of patient in follow-up studies.