Is the Small Fiber Neuropathy a Form of Diabetic Polyneuropathy?

초록

Objective: A small fiber neuropathy often presents with pain, tingling and cold sensation of extremities. Diabetes mellitus (DM) brings both vascular and metabolic peripheral neuropathies affecting small unmyelinated and large myelinated nerve fibers; and it is the most common cause of metabolic small fiber neuropathy with symptoms mentioned above. Nerve conduction study (NCS) has been regarded as standardized diagnostic tool for diabetic neuropathy. Since NCS represents the function of only large myelinated fibers it rarely evaluates small fiber neuropathies. On the other hand, thermoregulatory sweat test (TST) has been used to measure the function of small nerve fibers based on the perspiration of the whole body by inducing central sweating through core temperature control. This study is to investigate the usefulness of TST in examining of small fiber neuropathy in DM patients with neuropathic symptoms and to investigate its compatibility with NCS. Methods: We enrolled 6 DM patients who visited with paresthesia or pain of limbs. We excluded those who were diagnosed with diseases, other than DM, which might cause neuropathic symptoms as well. NCS included motor and sensory nerves in upper and lower extremities. TST was done in a heat-and-humidity-controlled thermoregulatory chamber, and the elevation of the patient’s core temperature was strictly controlled (at least 1.0oC above baseline temperature, or up to 38oC). Alizarin red was used as an indicator dye. Sweating pattern was analyzed by skin color change, and digital photography was taken to calculate the area of sweating by using rules of nine. Results: Four of 6 patients had tingling sensation on both upper and lower extremities, and four patients had limb pains. Mean HbA1c was 7.1%, which indicates mild increase and moderately-controlled blood glucose. On NCS one patient showed definite polyneuropathy and two with borderline abnormality. Five of 6 patients showed distal pattern of anhidros