Composite nerve conduction scores and signs for diagnosis and somatic staging of diabetic polyneuropathy: Mid North American ethnic cohort survey

Abstract

Introduction/aims: In the Diabetes Control and Complications Trial (DCCT), the minimal nerve conduction (NC) criterion for diabetic sensorimotor polyneuropathy (DSPN) was abnormality of NC in more than one peripheral nerve without specifying the attributes of NCs to be evaluated. In the present study, we assess individual and composite scores of NCs meeting the DCCT criterion and signs for improved diagnosis and assessment of DSPN severity.

Methods: Evaluated were 13 attributes and 6 composite NC scores and signs and symptoms in 395 healthy subjects (HS) and 388 persons with diabetes (DM).

Results: Percent abnormality between subjects with DM and HS was remarkably different among individual attributes and the six composite NC scores. For diagnosis of DSPN using the DCCT criterion, assessment of conduction velocities (CVs) and distal latencies (DLs) provided sensitive diagnoses of DSPN. NC amplitudes provided stronger measures of severity. In studied cohorts, DSPN was staged: N0, no NC abnormality using NC score 2 (CVs and DLs), 60.0%; N1, NC abnormality only, 18.4%; N2, NC abnormality and signs of feet or legs, 16.3%; and N3, NC abnormality and signs of thighs, 5.3%.

Discussion: For sensitive and standard diagnosis of DSPN using the DCCT NC criterion, specifically defined composite scores of CVs and DLs, e.g., score 2, is recommended. A composite score of amplitudes, e.g., score 4, provides a stronger measure of neuropathy severity. Also, provided are HS reference values of evaluated attributes of NCs and estimates of staged severity of DSPN of mid North American DM cohorts.

Keywords: composite nerve conduction scores; diabetic complication in Northern Plains Indians and Latinos; diagnosis of diabetic sensorimotor polyneuropathy; epidemiology survey of diabetic sensorimotor polyneuropathy; nerve conduction assessment and reference values in health and in diabetes; staged severity of diabetic sensorimotor polyneuropathy; validation of diagnosis and staged severity of diabetic sensorimotor polyneuropathy.

Figure 1:

Shown are the plotted individual values of motor nerve conduction velocities of ulnar, fibular, and tibial nerves and of sural nerve distal latency of healthy subjects, without diabetes, drawn from studied ethnic cohorts: RDNS, NPI, and Lat cohorts. Shown also is the 5^th percentile regression line on height for conduction velocities and the 95^th regression line for sural nerve distal latency. The percentile range difference related to age is indicated by showing the difference in a person aged 25 and 75 years. These reference values were used by us in formulating composite NC score #2 highly sensitive for the NC diagnosis of DSPN.

Figure 2:

Shown are individual values of the CMAPs of ulnar, fibular, and tibial nerves and of SNAP amplitudes of sural nerve, attributes of NCs assessed in composite score #4. Shown are the 5^th and 1^st percentile regression lines for each of the assessed attributes of NCs. Composite score #4 is not as sensitive for diagnosis of DSPN as is composite score #2, but is a more useful measure of severity of DSPN as detailed in Discussion.

Figure 3:

A plot of staged severity of DSPN in HS and persons with DM in studied mid North American ethnic cohorts. Stage 0 is without abnormality of composite NC score #2, of four sensitive CVs and DLs of limb nerves. Stage 1 persons have abnormality of composite NC score #2 without neuropathy signs. Stage 2 has NC abnormality and neuropathy signs of feet or legs. Stage 3 has NC abnormality and signs extending to the thighs.

Figure 4:

The ROC/AUC plots of different measures of DSPN as compared to composite NC score #2 of sensitive CVs and DLs of limb nerves. Individual sensitive MNCVs, as expected, have large AUCs. NIS and composite NC score #4 had intermediate AUC values and fibular CMAPs and sural SNAPs had lower values. This data indicates that composite score #2 of CVs and DLs are sensitive measures of DSPN especially useful for diagnosis. Composite score #4 of CMAP/SNAP amplitudes are less sensitive for the diagnosis of DSPN than composite score #2 but are valid measures of staged severity proposed in this report.