The prevalence by staged severity of various types of diabetic neuropathy, retinopathy, and nephropathy in a population‐based cohort
The Rochester Diabetic Neuropathy Study

The magnitude of the health problem from diabetic neuropathies remains inadequately estimated due to the lack of prospective population-based studies employing standardized and validated assessments of the type and stage of neuropathy as compared with background frequency. All Rochester, Minnesota, residents with diabetes mellitus on January 1, 1986, were invited to participate in a cross-sectional and longitudinal study of diabetic neuropathies (and also of other microvascular and macrovascular complications). Of 64,573 inhabitants on January 1, 1986 in Rochester, 870 (1.3%) had clinically recognized diabetes mellitus (National Diabetes Data Group criteria), of whom 380 were enrolled in the Rochester Diabetic Neuropathy Study. Of these, 102 (26.8%) had insulin-dependent diabetes mellitus (IDDM), and 278 (73.2%) had non-insulin-dependent diabetes mellitus (NIDDM). Approximately 10% of diabetic patients had neurologic deficits attributable to nondiabetic causes. Sixty-six percent of IDDM patients had some form of neuropathy; the frequencies of individual types were as follows: polyneuropathy, 54%; carpal tunnel syndrome, asymptomatic, 22%, and symptomatic, 11%; visceral autonomic neuropathy, 7%; and other varieties, 3%. Among NIDDM patients, 59% had various neuropathies; the individual percentages were 45%, 29%, 6%, 5%, and 3%. Symptomatic degrees of polyneuropathy occurred in only 15% of IDDM and 13% of NIDDM patients. The more severe stage of polyneuropathy, to the point that patients were unable to walk on their heels and also had distal sensory and autonomic deficits (stage 2b) occurred even less frequently–6% of IDDM and 1% of NIDDM patients. Overall, two thirds of diabetic patients have objective evidence for some variety of neuropathy, but only about 20% have symptoms, and only 6% of IDDM and only 1% of NIDDM patients have sufficiently severe polyneuropathy to be graded stage 2b, and none were graded stage 3. Approximately one quarter of patients had subclinical carpal tunnel syndrome, but only 7.7% had symptomatic carpal tunnel syndrome. Thus, diabetic peripheral neuropathy is frequent but less severe than generally thought. As generally believed, however, neuropathy, retinopathy, and nephropathy are significantly associated.