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Diabetes mellitus (type 1 and type 2) is the most common cause of peripheral neuropathy in Western countries and accounts for more diabetes-related hospitalizations than any other complication. The cause of diabetic neuropathy is not completely understood but some researchers theorize that the metabolic consequences of insulin deficiency and hyperglycemia (higher than normal levels of sugar in the blood) are related to the initial damage to the nerve fibers and vascular insufficiency, which is common in diabetes, and which may accelerate the neuropathic injury. Additional factors related to the development of diabetic peripheral neuropathy include duration of diabetes and obesity.

It appears that hypertension, age, smoking, and dyslipidemia may also elevate the risk of developing diabetic peripheral neuropathy.

Peripheral neuropathy is one of the most common long-term complications of diabetes. Estimates of incidence vary widely and range from approximately 10% to 90% with the average reported as approximately 60%. It occurs equally among type 1 and type 2 diabetes and has more of an effect on the quality of life of diabetic patients than other aspects of the condition, such as dietary restriction. The number of people affected by diabetic neuropathy increases with age (approximately 50% of diabetics over the age of 60) since it can develop several years after the onset of diabetes. It is important to distinguish the origin of the symptoms of peripheral neuropathy in the diabetic patient since up to 10% of diabetics may have signs of peripheral neuropathy from nondiabetic causes. It is not clear whether progression of diabetic neuropathy is closely related to controlling the level of glucose in the blood (glycemic control).

The most serious complication associated with diabetic neuropathy is foot ulceration which is due to:

• Loss of sensation in the feet (patient may not be aware of injury or pressure sores so it goes untreated)
• Abnormalities of motor function
• Autonomic involvement that causes dry, chapped skin because of reduced production of sweat
• Poor circulation to the extremities

Diabetic foot ulcers can lead to the onset of gangrene and may require amputation. The presence of neuropathy significantly increases the risk of amputation. By some estimates, diabetic neuropathy is responsible for up to 75% of non-trauma related amputations among diabetics. This highlights the need for diabetic patients to be screened for any signs of neuropathy even if there is no clinical evidence of neuropathy since early symptoms may be subacute or mild.

The progression of diabetic neuropathy differs for type 1 and type 2 diabetes. In type 1 diabetes, there is typically a rapid deterioration of nerve function soon after onset and then it slows, whereas, in type 2 diabetes, the nerve damage and symptoms of neuropathy are present at diagnosis and progress thereafter at a steady rate.

Diabetic neuropathy is typically a sensory neuropathy but often affects the autonomic nervous system as well. Nearly 50% of diabetic patients with neuropathy may have symptoms of autonomic peripheral neuropathy which can be mild or subclinical but, nevertheless, potentially life threatening. Symptoms associated with cardiac disease, (e.g., silent cardiac ischemia, orthostatic hypotension) can be fatal or can cause significant morbidity. Cardiac disease accounts for up to 25% of deaths of diabetic patients over a 10-year period from the time of diagnosis and is an independent risk factor for stroke. Medical professionals involved in the care and treatment of diabetic neuropathy include an endocrinologist, neurologist, rehabilitation specialist, and physical and/or occupational therapist. Other professionals who may be involved include a social worker or vocational counselor.