Variable relationship between peripheral somatic and autonomic neuropathy in patients with different syndromes of diabetic polyneuropathy.
The relationship between abnormal peripheral nerve electrophysiology and abnormal cardiovascular autonomic function has been studied in four groups of diabetic subjects, comparable with regard to age, duration, and type of diabetes. Thirty-three had no symptoms of neuropathy, 28 had newly developed painful neuropathy, 24 had chronic painful neuropathy, and 21 had painless neuropathy with associated recurrent foot ulcers. In all three symptomatic groups, electrophysiology and autonomic function were more abnormal than in asymptomatic diabetic subjects. There was a significant overall relationship between peripheral nerve (electrophysiologic) and autonomic (cardiovascular reflex) dysfunction. However, when considered by groups, the degree of cardiovascular reflex abnormality was similar in the three symptomatic groups, whereas electrophysiology was appreciably worse in the foot ulcer group than in patients with painful neuropathy. Thus, patients with painful neuropathy had a higher ratio of autonomic (small fiber) abnormality to electrophysiologic (large fiber) abnormality. By contrast, foot ulceration was associated with the worst electrophysiologic (large fiber) abnormality. Heavier alcohol consumption and more severe retinopathy were also related to foot ulceration. In diabetic subjects with symmetrical sensory neuropathy, the relationship between large fiber and small fiber damage is not uniform. We conclude that there may be different etiologic influences on large and small fiber neuropathy in diabetic subjects and that the predominant type of fiber damage may determine the form of the presenting clinical syndrome.