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Howe EE, Apollinaro M, Bent LR. Mechanoreceptor sensory feedback is impaired by pressure induced cutaneous ischemia on the human foot sole and can predict cutaneous microvascular reactivity. Front Neurosci 2024; 18:1329832. [PMID: 38629048 PMCID: PMC11019310 DOI: 10.3389/fnins.2024.1329832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 03/06/2024] [Indexed: 04/19/2024] Open
Abstract
Introduction The foot sole endures high magnitudes of pressure for sustained periods which results in transient but habitual cutaneous ischemia. Upon unloading, microvascular reactivity in cutaneous capillaries generates an influx of blood flow (PORH: post-occlusive reactive hyperemia). Whether pressure induced cutaneous ischemia from loading the foot sole impacts mechanoreceptor sensitivity remains unknown. Methods Pressure induced ischemia was attained using a custom-built-loading device that applied load to the whole right foot sole at 2 magnitudes (15 or 50% body weight), for 2 durations (2 or 10 minutes) in thirteen seated participants. Mechanoreceptor sensitivity was assessed using Semmes-Weinstein monofilaments over the third metatarsal (3MT), medial arch (MA), and heel. Perceptual thresholds (PT) were determined for each site prior to loading and then applied repeatedly to a metronome to establish the time course to return to PT upon unload, defined as PT recovery time. Microvascular flux was recorded from an in-line laser speckle contrast imager (FLPI-2, Moor Instruments Inc.) to establish PORH peak and recovery rates at each site. Results PT recovery and PORH recovery rate were most influenced at the heel and by load duration rather than load magnitude. PT recovery time at the heel was significantly longer with 10 minutes of loading, regardless of magnitude. Heel PORH recovery rate was significantly slower with 10minutes of loading. The 3MT PT recovery time was only longer after 10 minutes of loading at 50% body weight. Microvascular reactivity or sensitivity was not influenced with loading at the MA. A simple linear regression found that PORH recovery rate could predict PT recovery time at the heel (R2=0.184, p<0.001). Conclusion In populations with degraded sensory feedback, such as diabetic neuropathy, the risk for ulcer development is heightened. Our work demonstrated that prolonged loading in healthy individuals can impair skin sensitivity, which highlights the risks of prolonged loading and is likely exacerbated in diabetes. Understanding the direct association between sensory function and microvascular reactivity in age and diabetes related nerve damage, could help detect early progressions of neuropathy and mitigate ulcer development.
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Affiliation(s)
- Erika E. Howe
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
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Thabit MN, Sedky A, Sayed MA, Baddary HM, Mohamed M. Double-Shock Stimulation of the Superficial Radial Nerve Compared With Standard Medial Plantar Nerve Conduction in the Early Detection of Asymptomatic Diabetic Neuropathy: A Pilot Study. J Clin Neurophysiol 2018; 35:474-480. [PMID: 30247382 DOI: 10.1097/wnp.0000000000000522] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE Diabetes mellitus is a major public health problem. Diabetic polyneuropathy (DP) is one of the most common complications of diabetes mellitus. The early detection of DP is very important for timely treatment of symptoms and preventative foot care. METHODS Participants were sorted into 3 age- and sex-matched groups: 20 "healthy" individuals; 21 diabetic patients without DP symptoms, "asymptomatic"; and 24 diabetic patients suffering from symptoms consistent with DP, "symptomatic." All study participants had normal results on conventional nerve conduction studies. All groups underwent both medial plantar mixed nerve conduction (as a single-shock stimulation technique) and superficial radial nerve conduction (double-shock stimulation) measurements. Interstimulus intervals of 2 to 8 ms were used to record sensory nerve action potentials (SNAP) 1 and SNAP 2 for both stimuli. RESULTS We found statistically significant decreases in medial plantar NAPs' amplitude and conduction velocity, and SNAP1/SNAP2 ratios between the three groups, especially at smaller interstimulus intervals. CONCLUSIONS Both medial plantar mixed nerve conduction and double-shock superficial radial nerve stimulation are reliable methods for the early detection of asymptomatic DP. However, the medial plantar mixed nerve technique is easier and less time-consuming.
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Affiliation(s)
- Mohamed N Thabit
- Department of Neurology, Sohag University Hospital, Sohag University, Sohag, Egypt
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3
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Allen MD, Doherty TJ, Rice CL, Kimpinski K. Physiology in Medicine: neuromuscular consequences of diabetic neuropathy. J Appl Physiol (1985) 2016; 121:1-6. [PMID: 26989220 DOI: 10.1152/japplphysiol.00733.2015] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 03/17/2016] [Indexed: 02/07/2023] Open
Abstract
Diabetic polyneuropathy (DPN) refers to peripheral nerve dysfunction as a complication of diabetes mellitus. This condition is relatively common and is likely a result of vascular and/or metabolic disturbances related to diabetes. In the early or less severe stages of DPN it typically results in sensory impairments but can eventually lead to major dysfunction of the neuromuscular system. Some of these impairments may include muscle atrophy and weakness, slowing of muscle contraction, and loss of power and endurance. Combined with sensory deficits these changes in the motor system can contribute to decreased functional capacity, impaired mobility, altered gait, and increased fall risk. There is no pharmacological disease-modifying therapy available for DPN and the mainstay of treatment is linked to treating the diabetes itself and revolves around strict glycemic control. Exercise therapy (including aerobic, strength, or balance training-based exercise) appears to be a promising preventative and treatment strategy for patients with DPN and those at risk. The goal of this Physiology in Medicine article is to highlight important and overlooked dysfunction of the neuromuscular system as a result of DPN with an emphasis on the physiologic basis for that dysfunction. Additionally, we sought to provide information that clinicians can use when following patients with diabetes or DPN including support for the inclusion of exercise-based therapy as an effective, accessible, and inexpensive form of treatment.
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Affiliation(s)
- Matti D Allen
- School of Medicine, Queen's University, Kingston, Ontario, Canada; School of Kinesiology and Health Studies, Faculty of Health Sciences, Queen's University, Kingston, Ontario, Canada; School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada;
| | - Timothy J Doherty
- School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada; Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada; Department of Physical Medicine and Rehabilitation, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada; and
| | - Charles L Rice
- School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Ontario, Canada; Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Kurt Kimpinski
- Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
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Kleggetveit IP, Namer B, Schmidt R, Helås T, Rückel M, Ørstavik K, Schmelz M, Jørum E. High spontaneous activity of C-nociceptors in painful polyneuropathy. Pain 2012; 153:2040-2047. [DOI: 10.1016/j.pain.2012.05.017] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Revised: 05/07/2012] [Accepted: 05/15/2012] [Indexed: 02/07/2023]
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Krishnan AV, Lin CSY, Park SB, Kiernan MC. Axonal ion channels from bench to bedside: a translational neuroscience perspective. Prog Neurobiol 2009; 89:288-313. [PMID: 19699774 DOI: 10.1016/j.pneurobio.2009.08.002] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 08/17/2009] [Accepted: 08/17/2009] [Indexed: 12/13/2022]
Abstract
Over recent decades, the development of specialised techniques such as patch clamping and site-directed mutagenesis have established the contribution of neuronal ion channel dysfunction to the pathophysiology of common neurological conditions including epilepsy, multiple sclerosis, spinal cord injury, peripheral neuropathy, episodic ataxia, amyotrophic lateral sclerosis and neuropathic pain. Recently, these insights from in vitro studies have been translated into the clinical realm. In keeping with this progress, novel clinical axonal excitability techniques have been developed to provide information related to the activity of a variety of ion channels, energy-dependent pumps and ion exchange processes activated during impulse conduction in peripheral axons. These non-invasive techniques have been extensively applied to the study of the biophysical properties of human peripheral nerves in vivo and have provided important insights into axonal ion channel function in health and disease. This review will provide a translational perspective, focusing on an overview of the investigational method, the clinical utility in assessing the biophysical basis of ectopic symptom generation in peripheral nerve disease and a review of the major findings of excitability studies in acquired and inherited neurological disease states.
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Affiliation(s)
- Arun V Krishnan
- Translational Neuroscience Facility, University of New South Wales, Randwick, Sydney, NSW, Australia
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6
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Nakatani-Enomoto S, Bandoh M, Kita Y, Yamanouchi H, Enomoto H, Kimura T, Hashimoto K, Yahara O, Ugawa Y. Paired stimulation study of the median nerve sensory action potential in diabetic patients. Acta Neurol Scand 2008; 118:94-8. [PMID: 18279481 DOI: 10.1111/j.1600-0404.2007.00989.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVES Conventional nerve conduction studies (NCS) are not sensitive to detect mild diabetic neuropathy. In order to detect subtle changes, we compared the conventional NCS with the relative refractory period (RRP) measurement of the median sensory nerve action potential by a paired stimulation method. METHODS Subjects were 29 diabetic patients whose conventional NCS were all normal. They were divided into two groups: neurologically symptomatic and asymptomatic groups. Twenty-eight age-matched control subjects were also studied. RESULTS The RRP of the symptomatic diabetic patients (5.9 +/- 0.5 ms) and that of the asymptomatic patients (5.6 +/- 0.5 ms) was significantly longer than that of the control subjects (4.9 +/- 0.6 ms). There was no significant difference in RRP between the symptomatic and asymptomatic patients. This may be due to the fact that NCS reflects mainly large myelinated fiber function and early symptoms represent mainly thin myelinated or unmyelinated fiber function. CONCLUSIONS The RRP measurement could reveal some mild involvement of peripheral nerves undetectable by conventional NCS, even though they caused no clinical symptoms.
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Affiliation(s)
- S Nakatani-Enomoto
- Department of Neurology, Tokyo Metropolitan Geriatric Hospital, Tokyo, Japan.
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Krishnan AV, Lin CSY, Kiernan MC. Activity-dependent excitability changes suggest Na+/K+ pump dysfunction in diabetic neuropathy. Brain 2008; 131:1209-16. [PMID: 18362098 DOI: 10.1093/brain/awn052] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Affiliation(s)
- Arun V Krishnan
- Prince of Wales Medical Research Institute, Prince of Wales Clinical School, University of New South Wales, Randwick, Sydney, NSW, Australia
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8
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Krishnan AV, Lin CSY, Park SB, Kiernan MC. Assessment of nerve excitability in toxic and metabolic neuropathies. J Peripher Nerv Syst 2008; 13:7-26. [DOI: 10.1111/j.1529-8027.2008.00155.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Krishnan AV, Kiernan MC. Uremic neuropathy: clinical features and new pathophysiological insights. Muscle Nerve 2007; 35:273-90. [PMID: 17195171 DOI: 10.1002/mus.20713] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Neuropathy is a common complication of end-stage kidney disease (ESKD), typically presenting as a distal symmetrical process with greater lower-limb than upper-limb involvement. The condition is of insidious onset, progressing over months. and has been estimated to be present in 60%-100% of patients on dialysis. Neuropathy generally only develops at glomerular filtration rates of less than 12 ml/min. The most frequent clinical features reflect large-fiber involvement, with paresthesias, reduction in deep tendon reflexes, impaired vibration sense, muscle wasting, and weakness. Nerve conduction studies demonstrate findings consistent with a generalized neuropathy of the axonal type. Patients may also develop autonomic features, with postural hypotension, impaired sweating, diarrhea, constipation, or impotence. The development of uremic neuropathy has been related previously to the retention of neurotoxic molecules in the middle molecular range, although this hypothesis lacked formal proof. Studies utilizing novel axonal excitability techniques have recently shed further light on the pathophysiology of this condition. Nerves of uremic patients have been shown to exist in a chronically depolarized state prior to dialysis, with subsequent improvement and normalization of resting membrane potential after dialysis. The degree of depolarization correlates with serum K(+), suggesting that chronic hyperkalemic depolarization plays an important role in the development of nerve dysfunction in ESKD. These recent findings suggest that maintenance of serum K(+) within normal limits between periods of dialysis, rather than simple avoidance of hyperkalemia, is likely to reduce the incidence and severity of uremic neuropathy.
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Affiliation(s)
- Arun V Krishnan
- Prince of Wales Medical Research Institute and Prince of Wales Clinical School, University of New South Wales, Barker Street, Randwick, Sydney, NSW 2031, Australia
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Chen X, Levine JD. Mechanically-evoked C-fiber activity in painful alcohol and AIDS therapy neuropathy in the rat. Mol Pain 2007; 3:5. [PMID: 17319957 PMCID: PMC1819368 DOI: 10.1186/1744-8069-3-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Accepted: 02/23/2007] [Indexed: 11/10/2022] Open
Abstract
While altered activities in sensory neurons were noticed in neuropathic pain, caused by highly diverse insults to the peripheral nervous system, such as diabetes, alcohol ingestion, cancer chemotherapy and drugs used to treat AIDS, other infections and autoimmune diseases, as well as trauma, our understanding of how these various peripheral neuropathies manifest as altered neuronal activity is still rudimentary. The recent development of models of several of those neuropathies has, however, now made it possible to address their impact on primary afferent nociceptor function. We compared changes in mechanically-evoked C-fiber activity, in models of painful peripheral neuropathy induced by drinking ethanol (alcohol) or administering 2',3'-dideoxycytidine (ddC), a nucleoside reverse transcriptase inhibitor for AIDS therapy, two co-morbid conditions in which pain is thought to be mediated by different second messenger signaling pathways. In C-fiber afferents, ddC decreased conduction velocity. In contrast, alcohol but not ddC caused enhanced response to mechanical stimulation (i.e., decrease in threshold and increase in response to sustained threshold and supra-threshold stimulation) and changes in pattern of evoked activity (interspike interval and action potential variability analyses). These marked differences in primary afferent nociceptor function, in two different forms of neuropathy that produce mechanical hyperalgesia of similar magnitude, suggest that optimal treatment of neuropathic pain may differ depending on the nature of the causative insult to the peripheral nervous system, and emphasize the value of studying co-morbid conditions that produce painful peripheral neuropathy by different mechanisms.
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Affiliation(s)
- Xiaojie Chen
- Departments of Anatomy, Medicine and Oral and Maxillofacial Surgery, Division of Neuroscience, NIH Pain Center, University of California, San Francisco, CA 94143, USA
| | - Jon D Levine
- Departments of Anatomy, Medicine and Oral and Maxillofacial Surgery, Division of Neuroscience, NIH Pain Center, University of California, San Francisco, CA 94143, USA
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Nodera H, Kaji R. Nerve excitability testing and its clinical application to neuromuscular diseases. Clin Neurophysiol 2006; 117:1902-16. [PMID: 16631406 DOI: 10.1016/j.clinph.2006.01.018] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Revised: 01/16/2006] [Accepted: 01/23/2006] [Indexed: 11/22/2022]
Abstract
Non-invasive nerve excitability testing measures the membrane polarization, ion channel function and paranodal/internodal condition of peripheral nerves. This technique has been recently used for various neuromuscular disorders, such as pure motor conduction block in multifocal motor neuropathy, conduction block in carpal tunnel syndrome and Na(+) channel function disorders in diabetic neuropathy, to shed light on their pathophysiology. Here, we review the basics of ion channel functions and membrane properties that influence nerve excitability, the basic principles of nerve excitability testing and the reported findings in various disorders.
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Affiliation(s)
- Hiroyuki Nodera
- Department of Neurology, Graduate School of Medicine, Tokushima University, 2-50-1 Kuramoto, Tokushima 770-8503, Japan.
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Baslow MH, Guilfoyle DN. Functions Of N-Acetylaspartate and N-Acetylaspartylglutamate in Brain. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 576:95-112; discussion 361-3. [PMID: 16802707 DOI: 10.1007/0-387-30172-0_7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Morris H Baslow
- Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, New York 10962 USA.
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13
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Jørum E, Schmelz M. Chapter 29 Microneurography in the assessment of neuropathic pain. HANDBOOK OF CLINICAL NEUROLOGY 2006; 81:427-38. [DOI: 10.1016/s0072-9752(06)80033-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Krishnan AV, Kiernan MC. Altered nerve excitability properties in established diabetic neuropathy. ACTA ACUST UNITED AC 2005; 128:1178-87. [PMID: 15758031 DOI: 10.1093/brain/awh476] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The underlying cause of diabetic neuropathy remains unclear, although pathological studies have suggested an ischaemic basis related to microangiopathy, possibly mediated through effects on the energy-dependent Na+/K+ pump. To investigate the pathophysiology of diabetic neuropathy, axonal excitability techniques were undertaken in 20 diabetic patients with neuropathy severity graded through a combination of quantitative sensory testing (QST) using a vibratory stimulus, assessment of symptom severity using the Total Neuropathy Symptom Score (T-NSS) and measurement of glycosylated haemoglobin as a marker of disease control. To assess axonal excitability, compound muscle action potentials were recorded at rest from abductor pollicis brevis following stimulation of the median nerve, and stimulus-response behaviour, threshold electrotonus, a current-threshold relationship and the recovery of excitability were recorded in each patient. All patients had established neuropathy, with abnormalities of T-NSS present in all patients and QST abnormalities present in 65%. Compared with controls, diabetic neuropathy patients had significant reduction in maximal CMAP amplitude (P < 0.0005), accompanied by a 'fanning in' of threshold electrotonus. In addition, the strength-duration time constant was decreased in diabetic neuropathy patients and recovery cycles were altered with reductions in refractoriness, the duration of the relative refractory period, superexcitability and subexcitability. It is proposed that while the changes in threshold electrotonus with supportive findings in the current-threshold relationship are consistent with axonal depolarization, possibly mediated by a decrease in Na+/K+ pump activity, the alterations in the recovery cycle of excitability could be explained on the basis of a smaller action potential, reflecting a limitation on the nodal driving current imposed by a reduction in Na+ conductances.
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Affiliation(s)
- Arun V Krishnan
- Institute of Neurological Sciences, Prince of Wales Hospital, Sydney, NSW, Australia
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Rutkove SB, Chapman KM, Acosta JA, Larrabee JE. Foot temperature in diabetic polyneuropathy: innocent bystander or unrecognized accomplice? Diabet Med 2005; 22:231-8. [PMID: 15717867 DOI: 10.1111/j.1464-5491.2005.01486.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
AIM To explore mechanisms by which temperature could influence the pathogenesis and symptoms of diabetic polyneuropathy. METHODS We conducted a literature review attempting to identify mechanisms by which diabetic polyneuropathy could be affected by temperature. RESULTS Cooling can theoretically hasten the progression of diabetic polyneuropathy through several different mechanisms. Specifically, cooling can enhance neuronal ischaemia, increase formation of reactive oxygen species, slow axonal transport, increase protein kinase C activity, and interfere with immune function. Short-term temperature fluctuations (both warming and cooling) can initiate and exacerbate neuropathic pain by causing neuronal hyperexcitability and functional deafferentation. Although normal fluctuations of distal extremity temperature may be sufficient for these effects, impaired thermoregulation may make the distal extremities more susceptible to temperature extremes. Eventually, a 'vicious cycle' may ensue, resulting in neuronal deterioration with further disruption of temperature regulation. Limited epidemiological data suggest a higher prevalence of diabetic polyneuropathy in populations living in colder locations, supporting our hypothesis. CONCLUSIONS Variations in foot temperature may play an important but as yet unrecognized role in the development and symptoms of diabetic polyneuropathy. Further basic and clinical research exploring this concept could help elucidate the natural history of diabetic polyneuropathy and lead to novel therapeutic strategies.
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Affiliation(s)
- S B Rutkove
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
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Boërio D, Hogrel JY, Créange A, Lefaucheur JP. Méthodes et intérêt clinique de la mesure de la période réfractaire nerveuse périphérique chez l'homme. Neurophysiol Clin 2004; 34:279-91. [PMID: 15890161 DOI: 10.1016/j.neucli.2004.08.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2004] [Accepted: 08/03/2004] [Indexed: 11/17/2022] Open
Abstract
Immediately after action potential occurrence, owing to transient sodium channel inactivation, axon excitability is reduced for a short period of time, including the absolute refractory period, a first period of total inexcitability, followed by the relative refractory period. There are basically two different stimulation protocols to estimate axonal refractoriness, i.e. "paired-pulse" and "collision" techniques. Refractory period has been assessed in various conditions and appeared to depend on several physiological or methodological factors, featuring the type of nerve or the characteristics of the subject, but also the technique of stimulation or the method of data analysis. In addition, refractory periods can be altered by pathological conditions. Several studies showed prolonged refractory periods in patients suffering from alcoholic, diabetic or toxic neuropathies. Refractory period abnormality is a sensitive marker of axonal dysfunction as observed in Guillain-Barré syndrome, carpal tunnel syndrome or multiple sclerosis. Thus, the measurement of the refractory periods is a valuable tool to study the pathophysiology of peripheral nerves, complementary to standard nerve conduction studies. However, the application of these techniques in the routine practice of clinical neurophysiology remains limited.
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Affiliation(s)
- D Boërio
- Service de Physiologie, Explorations Fonctionnelles, Hôpital Henri-Mondor, AP-HP, 51, avenue du Maréchal-de-Lattre-de-Tassigny, Créteil, France
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Misawa S, Kuwabara S, Ogawara K, Kitano Y, Yagui K, Hattori T. Hyperglycemia alters refractory periods in human diabetic neuropathy. Clin Neurophysiol 2004; 115:2525-9. [PMID: 15465442 DOI: 10.1016/j.clinph.2004.06.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/08/2004] [Indexed: 02/07/2023]
Abstract
OBJECTIVE To investigate the effects of hyperglycemia on axonal excitability in human diabetics. Diabetic nerve dysfunction is partly associated with the altered polyol pathway and Na+-K+ ATPase activity, probably resulting in a decrease in the trans-axonal Na+ gradient and reduced nodal Na+ currents. METHODS Threshold tracking was used to measure the relative refractory periods (RPs) of median motor axons in 58 diabetic patients, 45 normal subjects, and 12 patients with non-diabetic axonal neuropathy. In diabetic patients, the relationship of RPs with hemoglobin A1c (HbA1c) levels was analyzed. RESULTS The mean RP was similar for diabetics and normal controls as a group, but was longer in patients with non-diabetic neuropathy than in normal controls (P=0.02). Diabetic patients with good glycemic control (HbA1c levels <7%) had longer RPs than patients with poorer glycemic control and normal controls (P=0.01). RP was longest at the HbA1c level of 6%, gradually decreasing and reaching a plateau at the HbA1c level of 8-9%. CONCLUSIONS Hyperglycemia shortens RPs, possibly because metabolic abnormalities lead to reduced nodal Na+ currents, and thereby to a lower inactivation of Na+ channels when generating an action potential. SIGNIFICANCE RP measurements could provide new insights into the ionic pathophysiology of human diabetic neuropathy.
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Affiliation(s)
- Sonoko Misawa
- Department of Neurology, Chiba University School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.
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Affiliation(s)
- Andrew J M Boulton
- Division of Endocrinology, University of Miami School of Medicine, P.O. Box 016960 (D-110), Miami, Florida, USA.
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Kitano Y, Kuwabara S, Misawa S, Ogawara K, Kanai K, Kikkawa Y, Yagui K, Hattori T. The acute effects of glycemic control on axonal excitability in human diabetics. Ann Neurol 2004; 56:462-7. [PMID: 15455400 DOI: 10.1002/ana.20232] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In diabetic nerves, the activation of the polyol pathway and a resulting decrease in Na(+)-K(+) ATPase activity lead to intra-axonal Na(+) accumulation and a smaller Na(+) gradient across the axolemma than normal. To investigate whether glycemic control is associated with acutely reversible changes in axonal excitability and Na(+) conductance, we measured the multiple excitability indices (strength-duration time constant, rheobase, refractoriness, and refractory period) of the median motor axons of 21 diabetic patients before and after intensive insulin treatment. Within 4 weeks after treatment was begun, there was a significant improvement in nerve conduction velocities, associated with increased strength-duration time constant, decreased rheobase, increased refractoriness, and prolonged refractory periods. Assuming that the strength-duration time constant partly reflects persistent Na(+) conductance, and that refractoriness/refractory periods depend on inactivation of transient Na(+) channels caused by prior depolarization (the influx of Na(+)), the patterns of changes in these indices may reflect a reduced trans-axonal Na(+) gradient during hyperglycemia and its restoration by glycemic control in diabetic patients. Measurement of the excitability indices could provide new insights into the pathophysiology of human diabetic neuropathy.
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Affiliation(s)
- Yukiko Kitano
- Department of Neurology, Chiba University School of Medicine, Chiba, Japan
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20
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Current literature in diabetes. Diabetes Metab Res Rev 2003; 19:248-55. [PMID: 12789659 DOI: 10.1002/dmrr.348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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