Electrophysiological patterns of diabetic polyneuropathy.

OBJECTIVE

This study evaluates the pattern of electrodiagnostic (EDX) abnormalities in diabetic sensorimotor polyneuropathies.

METHODS

EDX data from 112 consecutive patients with type 2 diabetes mellitus with distal, predominantly sensory, polyneuropathies were reviewed. Motor conduction velocities (CV), distal motor latencies (DML), compound muscle action potential (CMAP) amplitudes, distal to proximal amplitude ratios (PID), and F-wave latencies (FWL) were analyzed. Data were normalized based on normative reference values, and the proportion of nerves with abnormal values in the lower and upper limbs were evaluated. These data were also analyzed in relation to whether there was possible demyelinating versus axonal injury. Statistical analyses included comparison of the proportions of abnormal nerves in upper versus lower limbs as well as using Generalized Estimating Equations (GEE) to account for correlated observations for each patient between lower and upper limbs and adjusting for patient age effect.

RESULTS

CVs were significantly more abnormal in the legs than the arms (p < 0.0006) and decreased CMAP amplitudes meeting criteria for axonal injury were also more frequent in the legs (p < 0.0001). Using the GEE model, axonal injury was more common in the legs while demyelinating injury was more common in the arms based on FWLs, especially in younger persons (e.g., 40 years old vs. 50 years old). These differences are not readily explained by the duration of the diabetes.

CONCLUSION

Since in diabetics "axonal" type injury may be more common in the legs while "demyelinating" injury more frequent in the arms, this study emphasizes the limitation of this type of classification, and supports the idea that the pattern of EDX abnormalities in different types of neuropathies may be more helpful.