Effect of TENS on Sensory Parameters in Diabetic Polyneuropathy

Diabetic polyneuropathy is a common complication of diabetes that damages the nerves of the feet and legs. Besides causing pain, it gradually reduces the ability to feel light touch on the sole of the foot. This loss of protective sensation is important because it removes the warning signal that normally prevents unnoticed injuries, which can lead to foot ulcers. Transcutaneous electrical nerve stimulation (TENS) is a non-drug treatment that delivers mild electrical currents through the skin using surface electrodes. It is inexpensive, widely available, and generally well tolerated. Most previous studies of TENS in diabetic polyneuropathy have looked at whether it relieves pain. Far less is known about whether it affects touch sensation, and whether the frequency of the stimulation matters. This study compares three groups of patients with long-standing diabetic polyneuropathy. One group receives high-frequency TENS (100 Hz), one receives low-frequency TENS (5 Hz), and one receives sham stimulation at an intensity too low to have a treatment effect. Treatment is given five days a week for eight weeks, with electrodes placed on the calf and the sole of the foot. The main measure is the lightest touch a participant can feel on the big toe, tested with Semmes-Weinstein monofilaments before and after the eight-week period. Additional measures include electrical and pressure pain thresholds and questionnaires on pain, mood, and quality of life. Participants and the researchers performing the assessments do not know which group each participant is in.

Inclusion Criteria: * Type 1 or type 2 diabetes mellitus * Clinically confirmed diabetic peripheral polyneuropathy of at least five years' duration, diagnosed by an endocrinologist during routine outpatient follow-up on the basis of distal symmetric sensory symptoms together with abnormal bedside sensory testing * Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) score of 9 or above * Standardized Mini-Mental State Examination score above 24 * Glycated haemoglobin (HbA1c) below 8.5% * Wagner grade 0 feet (intact plantar skin without ulceration) * Willing to continue prescribed diet and hypoglycaemic treatment unchanged throughout the study Exclusion Criteria: * Use of a cardiac pacemaker * Alcohol dependence * Peripheral arterial disease * Renal failure * Hepatic failure * Hypothyroidism * Vitamin B12 deficiency * Folate deficiency * Sarcoidosis * Active infection * Malignancy * Coagulopathy * Skin lesion, discolouration, or allergic reaction at the electrode sites