Cigarette Smoking and Neuropathy in Diabetic Patients

We studied whether lifetime cigarette smoking is associated with the presence of diabetic neuropathy. The research design consisted of a case-control study conducted from a referral-based diabetes clinic at a major medical center. The patients were a 65% sample (163 insulin-dependent diabetes mellitus [IDDM] and 166 non-insulin-dependent diabetes mellitus [NIDDM] patients) of all patients admitted during a 26-mo period. Neuropathy was diagnosed on the basis of signs and symptoms. Smoking history was obtained by mailed questionnaire (66% response rate). Diabetes duration, HbA₁, age, sex, peripheral vascular disease, hypertension history, and lifetime alcohol consumption were measured as covariates. The prevalence of neuropathy was 49 and 38% in IDDM (n = 113) and NIDDM (n = 104) patients, respectively. In IDDM, but not NIDDM, current or ex-smokers were significantly more likely to have neuropathy than individuals who had never smoked (odds ratio 2.46, P = 0.02), and the prevalence of neuropathy increased with increasing number of pack-years smoked (P < 0.001). After adjustment for covariates, IDDM patients smoking ≥30 pack-yr were 3.32 times more likely to have neuropathy than patients smoking less than this amount (95% confidence interval 1.15–9.58, P = 0.026). Cigarette smoking was associated with the presence of neuropathy in this clinic-based population of IDDM patients. The hypothesis that cigarette smoking is associated with diabetic neuropathy should be investigated further, both prospectively and in a more representative population.