Small- and Large-Fiber Involvement in Early Diabetic Neuropathy: A Study With the Medial Plantar Response and Sensory Thresholds

Abstract

Small- and large-fiber function in diabetic neuropathy was studied in 68 patients (mean age 45.4 +/- 12.9 yr; 27 type I and 41 type II diabetics) with psychophysical tests of vibration and thermal sensation and neurophysiological measurements, including the medial plantar sensory action potential (MPSAP). Thermal sensitivity at the dorsolateral aspect of the foot (Pfizer thermal tester) correlated significantly with vibration thresholds (Somedic vibrameter) at three sites in the foot and two in the hand. Forty patients had normal sensory thresholds, but 18 of these lacked an MPSAP. Smaller groups had a single abnormal sensory threshold: 12 (18%) had an abnormal vibration threshold, and 24 (35%) had abnormal thermal sensitivity; 8 of the former group and 17 of the latter group lacked an MPSAP response. Only 8 (12%) had both abnormal vibration and thermal sensation (6 without an MPSAP). Fifteen of the 17 symptomatic patients had lost the MPSAP, but there was no consistent pattern of sensory loss. In this relatively young group of diabetics, more patients showed absent MPSAP responses than an abnormality in either sensory test on its own. The MPSAP is frequently absent in patients with no abnormalities in psychophysical tests of peripheral large-fiber function (vibration sensation) and small-fiber function (thermal sensitivity).

Quantitative measurement of cutaneous perception in diabetic neuropathy

“…Most of these studies used a hand-held instrument (bioesthesiometer) which is known to lack reproducibility. Levy et al 23 reported a coefficient of variation of 0.46 for thermal and 0.40-0.65 for vibratory threshold on three repeated testings. Kenshalo and BergenI8 reported a pronounced intraindividual consistency of thermal testing in a few well-trained subjects.…”

Thermal Threshold: Research Study on Small Fiber Dysfunction in Distal Diabetic Polyneuropathy

“…These techniques do not evaluate small fiber, which conduct autonomic function, sense cold, heat, and pain, and are altered earlier than thick fiber in DM patients and glucose intolerants. 15,[16][17][18][19][20] Hence our interest in comparing DSPN frequency in T2DM patients by using two different methods: (1) thermal threshold (TT) which studies small fiber function and (2) EMG and NC, which study large fiber function.…”

Diabetic neuropathy in patients with "Latent Autoimmune Diabetes of the Adults" (LADA) compared with patients with type 1 and type 2 diabetes

“…Electrophysiological testing led to the detection of abnormalities in a majority of patients with diabetes, even in patients who were free of neurological symptoms and of definite signs on the physical neurological examina- tion [13,1]. However, this study emphasized important differences concerning the development and course of diabetic neuropathy between LADA and type 2 diabetes patients.…”

“…Several tests are available for obtaining more quantitative information about the involvement of different types of nerve fibres [13]. Nerve conduction studies are useful for large myelinated motor and sensory nerve fibres.…”