Involvement of the peripheral and autonomic nervous systems is probably the most common complication of diabetes. Clinical diabetic neuropathy is categorized into distinct syndromes according to the neurologic distribution, although many overlap syndromes occur. In both type 1 and type 2 diabetes, the prevalence varies with both the severity and duration of hyperglycemia.
This topic will review the epidemiology and classification of diabetic neuropathy. Other aspects of diabetic neuropathy are discussed separately. (See "Pathogenesis and prevention of diabetic polyneuropathy" and "Clinical manifestations and diagnosis of diabetic polyneuropathy" and "Diabetic autonomic neuropathy" and "Treatment of diabetic neuropathy" and "Diabetic amyotrophy and idiopathic lumbosacral radiculoplexus neuropathy".)
Diabetic polyneuropathy is the most common neuropathy in the Western world . Clinical and subclinical neuropathy has been estimated to occur in 10 to 100 percent of diabetic patients, depending upon the diagnostic criteria and patient populations examined. Prevalence is a function of disease duration, and a reasonable figure, based upon several large studies, is that approximately 50 percent of patients with diabetes will eventually develop neuropathy [1-3].
The prevalence and incidence of diabetic polyneuropathy can be illustrated by the following observations:
- In a landmark study, over 4400 patient with diabetes were serially evaluated over 25 years [4-6]. Neuropathy was defined as decreased sensation in the feet and depressed or absent ankle reflexes. The onset of neuropathy correlated positively with the duration of diabetes and, by 25 years, 50 percent of patients had neuropathy.
- In a community-based study from northwest England of 15,692 patients with diabetes, the prevalence of clinical neuropathy, defined by the loss of pinprick, vibration, and temperature sensation, was 49 percent, while the prevalence of painful neuropathic symptoms was 34 percent . The prevalence of painful neuropathy symptoms accompanied by clinical neuropathy was 21 percent. The risk of painful neuropathy was increased in patients with type 2 diabetes, women, and those of South Asian ethnicity.
- In a cross-sectional multicenter study of 6487 diabetic patients in the United Kingdom, the overall prevalence of diabetic neuropathy was 28.5 percent . There was a correlation with disease duration such that the prevalence reached 44 percent in patients between 70 and 79 years of age. Patients were diagnosed with neuropathy if they had decreased or absent vibration, pin-prick, and temperature sensation at the great toe with reduced or absent ankle jerks and, if the signs were mild symptoms, such as burning, numbness, tingling, cramping, or aching.
- Two reports evaluated the incidence of new cases of diabetic neuropathy. In one, 231 patients with type 2 diabetes but no peripheral neuropathy were followed for a mean of 4.7 years . The incidence of new cases of distal symmetric sensory neuropathy was 6.1 per 100 person-years. As expected, the occurrence of neuropathy was associated with the level of hemoglobin A1C (HbA1c). A similar rate of new cases was described in a series of patients with type 1 diabetes . The incidence was increased in patients with hypertension (relative risk 4.1).
- In the UKPDS trial, 3867 newly diagnosed patients with type 2 diabetes were randomly assigned to either intensive therapy (sulfonylurea or insulin) or conventional therapy (diet control) . After ten years, absent ankle reflexes, as a sign of diabetic neuropathy, were noted in 35 and 37 percent, respectively.