Peripheral neuropathy is a term to describe damage to the peripheral nervous system, consisting of the nerve fibers that lie outside of the brain and spinal cord.
Many peripheral sensory neuropathies are length-dependent neuropathies, which means that the damage will be first exhibited in the periphery, meaning the feet and hands.
Peripheral sensory neuropathy can have many etiologies, one of the most common is Diabetes, but there may be many other origins like Herpes Zoster, Human Immunodeficiency Virus (HIV) or neuropathy due to neurotoxins like Chemotherapy-induced Poly-neuropathy (CIPN) are counted among its causes.
In addition, peripheral neuropathy is found in most patients suffering from renal disease, with polyneuropathy one of the most common consequences of chronic renal failure. The majority of these patients are asymptomatic, requiring electrophysiological testing to confirm the abnormality. The health of the peripheral nerve is recognized as an important, quantitative serial or longitudinal measure for the effectiveness of dialysis in uremic neuropathy.
Peripheral sensory neuropathy exhibits itself in different ways depending on the mechanism of the damage. It may affect large-diameter myelinated sensory fibers which are responsible for the sense of touch and vibration (gnostic sensitivity), or small diameter thinly or non-myelinated fibers that are responsible for the sense of temperature (warm and cold) and pain (vital sensitivity).
Methods are needed to quantitatively evaluate the integrity of both small and large-caliber sensory nerve fibers in order to detect, diagnose, and treat this condition early in its progression.
Quantitative sensory testing and peripheral sensory neuropathies
There are few methods available to test and quantify deficits in the function of peripheral sensory nerve fibers. Some of these methods, like EMG, or skin biopsy, can be painful and invasive, and in some conditions, hard to recuperate from.
Quantitative sensory testing (QST) allows to non-invasively test both gnostic and vital sensitivity. Research shows that QST may be able to detect sensory nerve deficits pre-clinically, before the patient complains of sensory disturbances, and can allow early intervention in this narrow window of opportunity.
For the smallest diameter nerve fibers (A-deta and C-fibers) thermal threshold testing is the only functional test available. Medoc’s thermal testing devices like the Pathway, TSA-II, TSA2, and Q-Sense have been widely tested, used, and validated on thousands of healthy controls and patients, with normative data for gender and age comparison available and integrated into the software. Our current thermal devices the TSA2, TSA2 Air and Q-Sense perform these tests for small fiber function.
Vibration testing is a sensitive and validated means to test the function of large-diameter (A-beta) sensory nerve fibers. Computerized vibration testing with Medoc’s VSA-3000 can allow precise and controlled vibration stimulation and comprehensive results. Vibratory thresholds have been described as an effective predictor of the risk of foot ulceration in diabetes. Several scientific conferences and organizations recommend the use of QST in treating and monitoring patients at risk for diabetic and metabolic neuropathies.