ABSTRACT
Diabetic neuropathy has been defined as a demonstrable disorder, either clinically evident or subclinical, that occurs in the setting of diabetes mellitus without other causes for peripheral neuropathy. It includes manifestations in the somatic and/or autonomic parts of the peripheral nervous system (1), which are classified along with clinical criteria. However, due to the variety of the clinical syndromes with possible overlaps there is no universally accepted classification. The most widely used classification of diabetic neuropathy, proposed by Thomas (2), has recently been modified (3). This proposal differentiates between rapidly reversible, persistent symmetric polyneuropathies, and focal or multifocal neuropathies (Table 1). The distal symmetric sensory or sensorimotor polyneuropathy (DSP) represents the most relevant clinical manifestation affecting approximately 30% of the hospital-based population and 20% of community-based samples of diabetic patients (4). The incidence of DSP is approximately 2% per year. The most important etiological factors that have been associated with DSP are poor glycemic control, visceral obesity, diabetes duration and height, with possible roles for hypertension, age, smoking, hypoinsulinemia, and dyslipidemia (4). Moreover, DSP is related to both lower-extremity impairments such as diminished position sense and functional limitations such as walking ability (5). There is accumulating evidence suggesting that not only surrogate markers of microangiopathy such as albuminuria but also those used for polyneuropathy such as nerve conduction velocity (NCV) and vibration perception threshold (VPT) may predict mortality in diabetic patients (6,7). Elevated VPT also predicts the development of neuropathic foot ulceration, one of the most common causes for hospital admission and lower limb amputations among diabetic patients (8). Pain associated with diabetic neuropathy exerts a substantial impact on the quality of life, particularly by causing considerable interference in sleep and enjoyment of life (9). Chronic neuropathic pain is present in 16% to 26% of diabetic patients (10,11). Pain is a subjective symptom of major clinical importance as it is often this complaint that motivates patients to seek health care. However, in a recent survey from the United Kingdom only 65% of diabetic patients received treatment for their neuropathic pain, although 96% had reported the pain to their physician (10). Pain treatment consisted of antidepressants in 43.5% of the cases, anticonvulsants in 17.4%, opiates in 39%, and alternative treatments in 30%. While 77% of the patients reported persistent pain over 5 years, 23% were pain free over at least 1 year (10). Thus, neuropathic pain persists in the majority of diabetic patients over periods of several years.
