VARIABLES INFLUENCING NEUROPATHIC END-POINTS - THE ROCHESTER DIABETICNEUROPATHY STUDY OF HEALTHY-SUBJECTS

We determined the normal limits for various neuropathic tests in healt hy subjects. The study, the Rochester Diabetic Neuropathy Study (RDNS) , is noteworthy because of its size (more than 400 subjects), random s election of subjects, and selection of at least 15 men and 15 women wi thout neuropathy, neurologic disease, or diseases predisposing to neur opathy from each hemidecade between 18 and 74 years of age from the po pulation of a defined region (Rochester, MN). Subjects were classified into those with (nonhealthy subjects, RDNS-NS) and without (healthy s ubjects, RDNS-HS) neuropathy, neurologic or psychiatric disease, or di seases known to predispose to neuropathy. The study provides normal li mits for tests used in the RDNS but it has broader uses as well. We fo und that (1) less than 10% of subjects in the third decade, approximat ely 20% in the fourth decade, and approximately 30% in the fifth or ol der decades were placed into the RDNS-NS category; (2) healthy subject s (RDNS-HS) retain their ability to walk on toes and heels regardless of age, excessive weight, or lack of physical fitness, but not their a bility to arise from a kneeled position-lost in more than 5% of person s 60 years and older; (3) the frequency of decreased or absent ankle r eflexes exceeds 5% in healthy subjects older than 50 years-limiting th eir value as a sign of diabetic polyneuropathy and necessitating a gra ding change with age in the neuropathy impairment score. We also found that (1) physical variables other than age influence neuropathic endp oints; (2) the variables are different among neuropathic endpoints; an d (3) it is now possible to compute specific percentile values automat ically for neuropathic endpoints for a given patient. We found that th e improved estimates of normal limits sometimes provide a different es timate of normality from the one that was available from age considera tion only. We suggest that the percentile approach considering physica l variables influencing neuropathic endpoints might be adopted by clin ical EMG, sensory, and autonomic laboratories. Continued use of normal limits tables, which are corrected only for age, provides quite inade quate reference values, especially for some attributes of nerve conduc tion and for the extremes of height and weight.