Diet-induced obesity decreases rate-dependent depression in the Hoffmann's reflex in adult mice

Rate-Dependent Depression of the Hoffmann Reflex: Practical Applications in Painful Diabetic Neuropathy

Measurement of the rate-dependent depression (RDD) of the Hoffmann (H) reflex, a technique developed over half a century ago, is founded on repeated stimulation of the H-reflex with tracking of sequentially evoked H-wave amplitudes in the resulting electromyogram. RDD offers insight into the integrity of spinal reflex pathways and spinal inhibitory regulation. Initially, RDD was predominantly utilized in the mechanistic exploration and evaluation of movement disorders characterized by spasticity symptoms, as may occur following spinal cord injury. However, there is increasing recognition that sensory input from the periphery is modified at the spinal level before ascending to the higher central nervous system and that some pain states can arise from, or be exaggerated by, disruption of spinal processing via a mechanism termed spinal disinhibition. This, along with the urgent clinical need to identify biological markers of pain generator and/or amplifier sites to facilitate targeted pain therapies, has prompted interest in RDD as a biomarker for the contribution of spinal disinhibition to neuropathic pain states. Current research in animals and humans with diabetes has revealed specific disorders of spinal GABAergic function associated with impaired RDD. Future investigations on RDD aim to further elucidate its underlying pathways and enhance its clinical applications.

Evidence of impaired H-reflex and H-reflex rate-dependent depression in diabetes, prediabetes and obesity: a mini-review

Diabetes Mellitus is a public health problem associated with complications such as neuropathy; however, it has been proposed that these may begin to develop during prediabetes and may also be present in persons with obesity. Diabetic peripheral neuropathy is the presence of signs and/or symptoms of peripheral nerve dysfunction in people living with diabetes, which increases the risk of developing complications and has a deleterious impact on quality of life. As part of the therapeutic protocol for diabetes, screening tests to identify peripheral neuropathy are suggested, however, there are no recommendations for people with prediabetes and obesity without symptoms such as pain, numbness, or paresthesias. Moreover, clinical screening tests that are usually used to recognize this alteration, such as tendon reflex, temperature sensation, and pressure and vibration perception, might be subjective as they depend on the evaluator's experience thus the incorrect application of these tests may not recognize the damage to small or large-nerve fibers. Recent evidence suggests that an objective study such as the impairment of the rate-dependent depression of the H-reflex could be used as a biomarker of spinal disinhibition and hence may provide more information on sensorimotor integration.

Impaired rate-dependent depression of the H-reflex in type-2 diabetes, prediabetes, overweight and obesity: A cross-sectional study

Type-2 diabetes is a chronic metabolic disorder characterized by hyperglycemia, resulting from deficits in insulin secretion or insulin resistance. According to the International Diabetes Federation, approximately 463 million people suffered from this condition in 2019, with a rapidly increasing impact in low-and middle-income countries. Obesity is a well-known risk factor for diabetes, and current data project a continuous increase in diabetes prevalence worldwide in obese individuals. Among the common complications, diabetic peripheral neuropathy (DPN) causes sensory symptoms, including pain that contributes to foot ulceration, and if not controlled, limb amputation may occur. The diagnosis of DPN is a clinical problem. Rate-dependent depression (RDD) of the Hoffmann reflex in the lower limbs has been proposed as a test to determine the presence of neuropathic pain in subjects with type-1 and type-2 diabetes. Recently, impaired RDD has been described in obese and diabetic rodent models. In this study, we characterized the RDD by evaluating the H-reflex at 0.2, 1, 2, 5, and 10 Hz in 39 patients with type-2 Diabetes mellitus (T2DM) and 42 controls without diabetes, subsequently classified as overweight/obese and prediabetic. A significant decrease in the RDD of the H-reflex was found in T2DM subjects at 1, 2, 5, and 10 Hz (P < .001) stimulation frequencies compared to controls, but not at 0.2 Hz (P = .48). A major finding of this study is that impaired RDD was also found in 11/25 overweight and obese subjects in at least 2 stimulation frequencies, being 10 of those classified in prediabetic levels according to their HbA1C values. The RDD of the H-reflex could be used as a quantitative and sensitive tool to study T2DM subpopulations with peripheral neuropathy. RDD could be used as a screening tool in combination with clinical tests to diagnose DPN and evaluate the progression of this condition.