Abstract
Background: Diabetic poly neuropathy, a common complication of diabetes, is diagnosed by symptoms, signs, physical examination, nerve conduction studies, and other neuro-physiological methods. Although nerve conduction studies are useful in the diagnosis and evaluation of diabetic neuropathy, there are difficulties in using them for the differential diagnosis of peripheral neuropathy because the pathological changes of diabetic neuropathy are varied.

Aims & Objective: To investigate the usefulness of a new parameter, the ratio of motor nerve conduction velocity to F-wave conduction velocity (M/F ratio), for the differential diagnosis of diabetic neuropathy.

Materials and Methods: Nerve conduction studies were conducted in 100 patients with diabetic neuropathy during the period of December 2012 to February 2013, 45 non diabetic patients with peripheral neuropathy, and 25 normal control participant. Non diabetic patients with neuropathy were grouped by clinical diagnosis as follows: segmental demyelination (n = 15), axonal neuropathy (n = 11), alcoholic poly neuropathy (n = 5), and other poly neuropathy (n = 14). Motor nerve conduction velocity (MCV) of post-tibial nerves, sensory nerve conduction velocity (SCV) of sural nerves, and F-wave conduction velocity (FWCV) of post-tibial nerves were measured by standardized techniques. The M/F ratio was calculated from these measurements.

Results: The motor conduction velocity (MCV) and sensory conduction velocity (SCV) of diabetic patients were significantly slower and the M/F ratio was significantly lower than those of normal participants: MCV, 43.7 ± 5.4 vs. 47.1 ± 2.9 m/s, P < 0.001; SCV, 44.7 ±11.1 vs. 48.3 ± 5.7 m/s, P < 0.05; M/F ratio, 0.84 ± 0.09 vs. 0.90 ± 0.06, P < 0.001. The FWCV of non-diabetic patients with neuropathy was significantly slower (40.0 ± 6.3 vs. 48.3 ± 4.0 m/s, P < 0.001) and the M/F ratio was significantly higher (1.04 ± 0.12, P < 0.001) than that of normal participants, respectively. Although MCV, SCV, and FWCV were correlated with age in normal control participants, the M/F ratio was independent of age in the diabetic as well as the non-diabetic patients with neuropathy.

Conclusion: Results suggest that the M/F ratio, which is influenced by the neuronal damages in the distal segment of peripheral nerves, is useful in the differential diagnosis of diabetic neuropathy.

Key words: Diabetes; F Waves; Neuropathy; Polyneuropathy