The refractory period of an axon is the time during which the ability to conduct an action potentials is altered following initiation and propagation of a nerve impulse. A refractory period is demonstrable in peripheral motor and sensory nerves in response to repetitive stimulation, and is influenced by the diameter of the axons comprising the nerve. To evaluate the usefulness of measuring the refractory period in early diagnosis of diabetic polyneuropathy, we compared the absolute, relative, and true relative refractory period of the distal portion of the sensory median nerve of 20 healthy controls to those of 20 diabetic patients (Group I) without evidence of polyneuropathy in conventional nerve conduction studies and 29 diabetic patients (Group II) with polyneuropathy.

The results were as follows;

1) The fasting and postprandial 2 hour blood sugars were not significantly different between group I & II. The HbA1c level was significantly higher in group II.

2) The absolute, relative, and true relative refractory period were 0.74±0.04, 3.26±0.14, 2.51±0.16 msec in healthy controls, 0.73±0.03, 3.72±0.23, 2.99±0.22 msec in group I, and 0.75±0.03, 4.23±0.48, 3.48±0.47 msec in group II, respectively.

3) There was no significant difference in absolute refractory period, but the relative and true relative refractory period were longer in group II than in group I and were loner in group I than in healthy controls.

4) In group II, the true relative refractory period was longer in patients with axonal degeneration and demyelination than those with demyelination only. Therefore, the axonal degeneration might be a major factor affecting relative refractory period.

With above results, the refractory period measurement is a useful method for early diagnosis of diabetic sensory neuropathy.

Keywords :Diabetic mellitus, Absolute refractory period, Relative refractory period, True relative refractory period