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Distal symmetric polyneuropathy can be further subdivided into small nerve fiber and large nerve fiber involvement.

Small Fiber Neuropathy

Small fiber pain is not well understood. It is thought that hyperglycemia may play a role in the increased sensitivity to pain caused by the damage of these fibers. Diabetic neuropathy seems to progress as these fibers (c-fibers) are damaged and sensitivity to pain is affected, causing pain of various intensity and severity. When the situation becomes chronic, there is no longer need for a stimulus to cause the pain, it is always present. Eventually, the fibers may die at which time the patient may no longer experience pain and may experience numbness.

Large Fiber Neuropathy

Large nerve fibers are myelinated and are associated with functions such as motor function, perception of vibration, sense of position, and perception of cold. Symptoms of large fiber neuropathy may be mild to severe and include:

• Impaired sense of vibration
• Dull pain in the bones of the lower leg or foot
• 'Hot foot' due to increased blood flow
• Shortened Achilles tendon

Most cases of diabetic neuropathy are a mixture of large and small fiber damage. Many patients experience the "glove or stocking" distribution of pain in the legs as an early sign of sensory loss.

Although some pain in diabetic neuropathy may resolve on its own, if the pain persists for more than 3 months, it is less likely to disappear. While symptoms from large fiber involvement (e.g., weakness, poor coordination) affect daily activities and may make a person more prone to falling, the effects of small fiber damage are more debilitating and significantly affect the overall wellbeing of the person since the pain be very intense, frequent, and/or last a long time.