Sweating impairment in patients with multiple sclerosis

Autonomic nervous system disorders in multiple sclerosis

Multiple sclerosis (MS) is a chronic progressive demyelinating disease of the central nervous system (CNS), which also affects the autonomic nervous system (ANS). Manifestations of MS in the ANS include urological, sexual, gastrointestinal, cardiovascular, and thermoregulatory disorders as well as increased fatigue. These problems are common yet are often underestimated due to the non-specificity of the symptoms and the limited evaluation of the ANS in the usual clinical practice. Most of these symptoms seem to be related to localized lesions in the CNS. However, the mechanisms by which these disorders are caused in MS have not been fully investigated, thus preventing any focused etiological treatment. The most common disorders of the ANS in MS represent a challenge for clinicians due to the variability of the clinical picture and our minimal data on their diagnosis and treatment. Early diagnosis and initiation of individualized treatment regimens, often in need of multiple approaches, seem to yield the best results in managing ANS dysfunction in MS patients.

How to explore and explain autonomic changes in multiple sclerosis

Autonomic dysfunction (AD) in people with MS (pwMS) is a frequent finding. This narrative review will present an overview of central neural mechanisms involved in the control of cardiovascular and thermoregulatory systems, and methods of autonomic nervous system testing will be discussed thereafter. Since the need for standardization of autonomic nervous system (ANS) testing, we will focus on the standard battery of tests (blood pressure and heart rate response to Valsalva maneuver and head-up tilt, and heart rate response to deep breathing test plus one of the tests for sudomotor function), which can detect ANS pathology in the majority of pwMS. The review will briefly discuss the other types of AD in pwMS and the use of appropriate tests. While performing ANS testing in pwMS one has to consider the multiple sclerosis phenotypes, disease duration, and its activity, the degree of clinical disability of patients included in the study, and the disease-modifying therapies taken, as these factors may have a great influence on the results of ANS testing. In other words, detailed patient characteristics presentation and patient stratification are beneficial when reporting results of ANS testing in pwMS.

Multiple sclerosis-related heat sensitivity linked to absence of DMT prescription and subjective hand impairment but not autonomic or corticospinal dysfunction

OBJECTIVES

Heat sensitivity (HS) describes a temporary worsening of multiple sclerosis (MS) symptoms with increased body temperature. The pathophysiology may relate to central nervous system conduction deficits and autonomic dysfunction. We conducted deep clinical phenotyping of a cohort of persons with MS to identify predictors of HS.

METHODS

We recruited 59 MS participants with HS or No HS. Participants self-reported symptom severity (Hospital Anxiety and Depression Scale, Multiple Sclerosis Impact Scale, and fatigue visual analog scale) and underwent maximal exercise and transcranial magnetic stimulation testing to characterize autonomic and corticospinal function. We examined associations with HS using binomial logistic regression.

RESULTS

People with HS (36/59) had significantly greater disability, depression, fatigue, and physical and psychological functional effects of MS. They also had significantly lower corticospinal excitability but not conduction. After controlling for disease-modifying therapy (DMT), disability, and disease type, self-reported difficulty using hands in everyday tasks was significantly associated with a large increase in the odds of HS. Autonomic and corticospinal dysfunction were not associated with HS. Lack of DMT use alone was also associated with a large increase in the odds of HS.

DISCUSSION

Following a comprehensive assessment of plausible contributors to HS, HS was most strongly associated with lack of a DMT prescription and self-reported hand dysfunction. Surprisingly, objective measurement of autonomic and corticospinal integrity did not contribute to HS.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Thermal dysregulation in patients with multiple sclerosis during SARS-CoV-2 infection. The potential therapeutic role of exercise

Thermoregulation is a homeostatic mechanism that is disrupted in some neurological diseases. Patients with multiple sclerosis (MS) are susceptible to increases in body temperature, especially with more severe neurological signs. This condition can become intolerable when these patients suffer febrile infections such as coronavirus disease-2019 (COVID-19). We review the mechanisms of hyperthermia in patients with MS, and they may encounter when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Finally, the thermoregulatory role and relevant adaptation to regular physical exercise are summarized.

Understanding and managing autonomic dysfunction in persons with multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is a chronic demyelinating immune mediated disease of the central nervous system. Autonomic dysfunction (AD) is frequently present in persons with MS (pwMS) and increases with disease duration and progression.

AREAS COVERED

Cardiovascular, genitourinary, and sudomotor autonomic dysfunction in pwMS are reviewed and managing of these disorders is addressed.

EXPERT OPINION

AD in pwMS can manifest with a myriad of symptoms including cardiovascular, urogenital, and sweating disorders. These symptoms can significantly impact the quality of life of pwMS with poor tolerance of upright position, difficulties in sexual function, and low endurance of physical activity especially in warm environments. Health professionals involved in care of pwMS should possess basic knowledge of the function of the autonomic nervous system and be informed of the way disorders of the autonomic function may manifest in pwMS in order to provide the proper care.

Sauna use as a lifestyle practice to extend healthspan

Sauna use, sometimes referred to as "sauna bathing," is characterized by short-term passive exposure to high temperatures, typically ranging from 45 °C to 100 °C (113 °F to 212 °F), depending on modality. This exposure elicits mild hyperthermia, inducing a thermoregulatory response involving neuroendocrine, cardiovascular, and cytoprotective mechanisms that work in a synergistic fashion in an attempt to maintain homeostasis. Repeated sauna use acclimates the body to heat and optimizes the body's response to future exposures, likely due to the biological phenomenon known as hormesis. In recent decades, sauna bathing has emerged as a probable means to extend healthspan, based on compelling data from observational, interventional, and mechanistic studies. Of particular interest are the findings from large, prospective, population-based cohort studies of health outcomes among sauna users that identified strong dose-dependent links between sauna use and reduced morbidity and mortality. This review presents an overview of sauna practices; elucidates the body's physiological response to heat stress and the molecular mechanisms that drive the response; enumerates the myriad health benefits associated with sauna use; and describes sauna use concerns.

Peripheral nervous system in multiple sclerosis-understanding the involvement via autonomic nervous system

AIM

The aim of this review is to summarize the clinical and paraclinical findings that demonstrate that multiple sclerosis (MS) affects the peripheral nervous system (PNS) as well as the central nervous system (CNS). Methods: Narrative review.

RESULTS

MS is traditionally defined as a chronic demyelinating immune-mediated disease of the CNS. However, there is emerging evidence that MS is a disease that does not solely affect the CNS but can manifest with PNS involvement as well. Several pathology studies have reported on signs of demyelination in the PNS, as well as on structural and functional involvement of the PNS in persons with MS (pwMS). From the functional aspect, several studies have shown autonomic nervous system (ANS) involvement in the form of sudomotor dysfunction measured with quantitative sudomotor axon reflex test (QSART) in different stages of MS, adding to the growing body of evidence that indicate PNS involvement in MS. In this review the clinical, pathological, neurophysiological, and imaging findings that demonstrate that MS affects the PNS as well as the CNS are summarized, with the emphasis on the ANS abnormalities.

CONCLUSION

Further large-scale research is needed in order to fully understand the frequency and importance of PNS affection in MS.

Frequency and characteristics of dysautonomic symptoms in multiple sclerosis: a cross-sectional double-center study with the validated Italian version of the Composite Autonomic Symptom Score-31

BACKGROUND

Dysautonomic symptoms (DS) are frequent but often underrecognized in multiple sclerosis (MS) patients, despite the relevant impact on quality of life and physical performance.

OBJECTIVES

To assess frequency and characteristics of DS in our MS population compared with healthy controls (HC). To investigate the relationship between DS and disease characteristics (MS subtype, disease duration, Expanded Disability Status Scale (EDSS), clinical and/or radiological activity, disability progression).

PATIENTS AND METHODS

Cross-sectional study includes 324 MS patients (mean age 44.9 ± 10.7 years; 66% female) and 190 HC (mean age 40.60 ± 12.83 years; 63% female). DS were assessed using the Italian validated version of the Composite Autonomic Symptom Score-31 (COMPASS-31). Possible confounding factors were considered.

RESULTS

More than 94% of enrolled MS patients reported alterations in ≥ 2 domains of the COMPASS-31 scale (score > 0) and significantly higher COMPASS-31 total and single domain median scores compared with HC, independently from possible confounding factors (orthostatic intolerance: p = 0.001; vasomotor: p = 0.017; secretomotor: p = 0.040; gastrointestinal: p = 0.047; bladder: p < 0.001; pupillomotor: p < 0.001; COMPASS-31 total score: p < 0.001). COMPASS-31 total, secretomotor, gastrointestinal, and bladder domain scores showed weak to moderate correlation with disease duration (Rho = 0.19, p < 0.001; Rho = 0.18, p = 0.01; Rho = 0.25, p = 0.030; Rho = 0.28, p < 0.001, respectively). A moderate correlation between EDSS score, COMPASS-31 total, and bladder domain scores (Rho = 0.32, p < 0.001 and Rho = 0.48, p < 0.001, respectively) was observed. Progressive subtypes showed higher COMPASS-31 total (p = 0.025), gastrointestinal (p = 0.07), and bladder (p < 0.001) domain scores vs relapsing-remitting patients.

CONCLUSIONS

Our findings confirm that MS-related DS are frequent and tend to increase paralleling disease duration and clinical worsening, reaching the highest clinical impact in progressive subtypes.

Association between diurnal temperature range and emergency department visits for multiple sclerosis: A time-stratified case-crossover study

Although multiple sclerosis (MS) has been the leading cause of neurologically-induced disability in young adults, risk factors for the relapse and acute aggravation of MS remain unclear. A few studies have suggested a possible role of temperature changes on the relapse and acute aggravation of MS. We investigated the association between short-term exposure to wide diurnal temperature ranges (DTRs) and acute exacerbation of MS requiring an emergency department (ED) visit. A total of 1265 patients visited EDs for acute aggravation of MS as the primary disease in Seoul between 2008 and 2014 from the national emergency database. We conducted a conditional logistic regression analysis of the time-stratified case-crossover design to compare DTRs on the ED visit days for MS and those on control days matched according to the day of the week, month, and year. We examined possible associations with other temperature-related variables (ambient temperature, between-day temperature change, and sunlight hours). Short-term exposure to wide DTRs immediately increased the risk of ED visits for MS. Especially, 2-day average (lag0-1) DTR levels on the day of and one day prior to ED visits exhibited the strongest association (an 8.81% [95% CI: 3.46%-14.44%] change in the odds ratio per 1 °C increase in the DTR). Other temperature-related variables were not associated with MS aggravation. Our results suggest that exposure to wider DTR may increase the risk of acute exacerbation of MS. Given the increasing societal burden of MS and the increasing temperature variability due to climate change, further studies are required.

Impaired Thermoregulatory Function during Dynamic Exercise in Multiple Sclerosis

INTRODUCTION

Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared with healthy controls (CON) exercising at similar rates of metabolic heat production.

METHODS

Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass-, and BSA-matched CON during a single bout of cycling exercise (rate of metabolic heat production: ∼4.5 W·kg) for 60 min in a climate-controlled room (25°C, 30% RH).

RESULTS

Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS, 72 ± 51 g; CON, 104 ± 37 g; P = 0.04) and 60 min (MS, 209 ± 94 g; CON, 285 ± 62 g; P = 0.02), as well as lower sweating thermosensitivity (MS, 0.49 ± 0.26 mg·cm·min·°C; CON, 0.86 ± 0.30 mg·cm·min·°C; P = 0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30- or 60-min time points (P > 0.05). Cutaneous vasculature responses were also not different in MS compared with CON (P > 0.05).

CONCLUSION

Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.

Progressive multiple sclerosis patients have a higher burden of autonomic dysfunction compared to relapsing remitting phenotype

OBJECTIVE

To determine autonomic dysfunction (AD) differences in patients with relapsing remitting multiple sclerosis (pwRRMS) and progressive MS (pwPMS).

METHODS

Composite autonomic scoring scale (CASS) and heart rate variability (HRV) were performed in 40 pwRRMS and 30 pwPMS.

RESULTS

pwPMS had a significantly higher sudomotor index and total CASS score compared to pwRRMS (p < 0.001 and p < 0.001, respectively). Disease duration positively correlated with sudomotor index and total CASS (r_s = 0.409, p < 0.001 and r_s = 0.472, p < 0.001, respectively), while the Expanded Disability Status Scale (EDSS) positively correlated with sudomotor index and total CASS (r_s = 0.411, p < 0.001 and r_s = 0.402, p = 0.001, respectively) in all patients. Type of multiple sclerosis (pwRRMS or pwPMS) corrected for age, sex and disease duration, was a statistically significant predictor of CASS value (B = 1.215, p = 0.019). Compared to pwRRMS, pwPMS had a significantly lower standard deviation of NN intervals (SDNN), low frequency (LF), and high frequency (HF), during both the supine and tilt-up phases (all p-values <0.006). pwPMS had a significantly lower LF/HF (p = 0.008) during tilt-up.

CONCLUSION

There is a significant difference in autonomic function in pwRRMS and pwPMS; with pwPMS having a higher burden of AD, which is particularly evident for sweating dysfunction.

SIGNIFICANCE

Further research is needed to establish whether parasympathetic and sudomotor dysfunction may serve as markers of progressive MS.

Thermoregulatory dysfunction in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurologic disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurologic symptoms with heat exposure (Uhthoff's phenomenon). This heat intolerance in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. Isolating and interpreting mechanisms responsible for autonomic dysfunction due to MS can be difficult as it may involve sensory impairments, altered neural integration within the central nervous system, impaired effector responses, or combinations of all of these factors. MS lesions occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacologic) for the MS patient to preserve function and decrease symptom worsening during heat stress. This review focuses on four main themes influencing current understanding of thermoregulatory dysfunction in MS: (1) heat intolerance; (2) central regulation of body temperature; (3) thermoregulatory effector responses; and (4) countermeasures to improve or maintain function during thermal stress.

Impaired sweating responses to a passive whole body heat stress in individuals with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system (CNS), disrupting autonomic function. The aim of this study was to test the hypothesis that individuals with MS have blunted control of thermoregulatory reflex increases in sweat rate (SR) and cutaneous vasodilation compared with controls during a passive whole body heat stress (WBH). Eighteen individuals with relapsing-remitting MS and 18 healthy controls (Con) participated in the study. Core temperature (T_core), skin temperature, heart rate, arterial blood pressure (10-min intervals), skin blood flow (laser-Doppler flux, LDF), and SR were continuously measured during normothermic baseline (34°C water perfusing a tube-lined suit) and WBH (increased T_core 0.8°C via 48°C water perfusing the suit). Following WBH, local heaters were warmed to 42°C, inducing peak cutaneous vasodilation at the site of LDF collection. Cutaneous vascular conductance (CVC) was calculated as the ratio of LDF to mean arterial pressure and expressed as a percentage of peak achieved during local heating. Individuals with MS had attenuated SR responses to WBH (ΔSR from baseline: Con, 0.65 ± 0.27; MS, 0.42 ± 0.17 mg·cm^-2·min^-1, P = 0.003), whereas Δ%CVC_42C from baseline was similar between groups (Con, 42 ± 16%; MS, 38 ± 12%, P = 0.39). SR responses were blunted as a function of T_core in MS (interaction: group × T_core, P = 0.03), of which differences were evident at ΔT_core 0.7°C and 0.8°C (P < 0.05). No interaction was observed in Δ%CVC_42C Taken together, the findings show MS blunts sweating responses, whereas control of the cutaneous vasculature is preserved, in response to WBH.NEW & NOTEWORTHY This study is the first to assess the reflex control of the thermoregulatory system in individuals living with multiple sclerosis (MS). The novel findings are twofold. First, attenuated increases in sweat rate in subjects with MS compared with healthy controls were observed in response to a moderate increase (0.8°C) in core temperature via passive whole body heat stress. Second, it appears the reflex control of the cutaneous vasculature is preserved in MS.

Autonomic Dysregulation in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, progressive central neurological disease characterized by inflammation and demyelination. In patients with MS, dysregulation of the autonomic nervous system may present with various clinical symptoms including sweating abnormalities, urinary dysfunction, orthostatic dysregulation, gastrointestinal symptoms, and sexual dysfunction. These autonomic disturbances reduce the quality of life of affected patients and constitute a clinical challenge to the physician due to variability of clinical presentation and inconsistent data on diagnosis and treatment. Early diagnosis and initiation of individualized interdisciplinary and multimodal strategies is beneficial in the management of autonomic dysfunction in MS. This review summarizes the current literature on the most prevalent aspects of autonomic dysfunction in MS and provides reference to underlying pathophysiological mechanisms as well as means of diagnosis and treatment.

Aquatic training in MS: neurotherapeutic impact upon quality of life

Three fundamental principals associated with aquatic therapy differentiate it with respect to exercise on land, and in air. These are buoyancy (reduction in weight of the body within the buoyant medium of water), viscosity (a “drag force” is generated when moving within water, when compared with the same movement in air), and the thermodynamic aspect of water exercise, during which the heat capacity of water is about 1000 times greater than that of an equivalent amount of air; equating to a heat transfer from the body into water at a rate 25 times faster than that of air. Aquatic conditioning, can improve neurologic functioning, with dividends favorably impacting activities of daily living, health maintenance, safety, and ultimately quality of life. Here, we review the application of aquatic exercise training in MS patients.

Autonomic dysfunction in multiple sclerosis: implications for exercise

Multiple sclerosis (MS), a progressive neurological disease, can result in autonomic dysfunction. Impairments in the autonomic control of cardiovascular and thermoregulatory function during exercise have been observed in MS. Attenuated elevations in blood pressure during exercise in MS patients can negatively impact blood flow to skeletal muscle. Diminished sweating during exercise may impair heat dissipation likely limiting the exercise intensity that can be performed before detrimental core temperatures are reached. Further understanding the physiologic mechanisms of autonomic dysfunction during exercise in MS may lead to the development of novel therapeutic strategies targeted at improving quality of life in individuals with this disease.

Autonomic dysfunction in multiple sclerosis

Multiple sclerosis (MS) is the leading cause of neurological disability in young adults. Since the pathophysiology of MS is characterized by dissemination in space, as well as in time, the autonomic nervous system is inevitably damaged in the course of the disease in many patients and the proportion of affected patients increases with disease duration. Autonomic dysfunction (AD) in MS is explained by lesions in regions responsible for autonomic regulation such as nuclei in the periventricular region of fourth ventricle in the brainstem as well as medullar lesions. Reports about frequency of AD in MS patients vary notably between groups. Nevertheless its impact on quality of life is substantial but, unfortunately, often overlooked. The aim of this article is to present a concise review of various symptoms and signs of autonomic system dysfunction in MS.

[Autonomic nervous system alteration in multiple sclerosis patients with urinary symptoms. Clinical, urodynamic and cardiovascular study]

OBJECTIVE

To assess symptoms related to autonomic nervous system alteration in a population of patients suffering from multiple sclerosis (MS) and presenting with urinary symptoms.

PATIENTS AND METHODS

We investigated 65 patients (mean age 47.5 years) suffering from MS, and presenting with urological dysfunction by means of symptom scores, urodynamic investigation, cardiovascular autonomic function tests (orthostatic hypotension testing, Valsalva test, deep breath test, cold pressor test) and sympathetic skin responses.

RESULTS

Forty-five (69%) patients suffered from overactive bladder, 48 (73%) from voiding dysfunction, 14 (21%) from urinary retention and 13 (20%) from fecal incontinence. Urodynamic investigation demonstrated overactive detrusor in 46 (70%) cases, and underactive detrusor in four (6%) cases. Twenty-five (38%) patients had dysautonomia without correlation neither with clinical or urodynamic data, nor gravity of multiple sclerosis (EDSS).

CONCLUSION

In this series, the prevalence of dysautonomia was high in patients suffering from MS and presenting with urinary disorders.

Sensitivity to heat in MS patients: a factor strongly influencing symptomology--an explorative survey

BACKGROUND

Many individuals diagnosed with Multiple Sclerosis (MS) are sensitive to increased body temperature, which has been recognized as correlating with the symptom of fatigue. The need to explore this association has been highlighted. The aim of this study was to investigate the occurrence of heat sensitivity and its relations to disease course, disability, common MS-related symptoms and ongoing immunosuppressive treatments among individuals 65 years of age or younger diagnosed with MS.

METHODS

A cross-sectional designed survey was undertaken. A questionnaire was sent to MS-patients with an Expanded Disability Status Score (EDSS) in the interval of 0-6.5 and who were between 20 and 65 years of age, living in an eastern region of Sweden (n = 334). Besides occurrence of heat sensitivity (Yes/No) and corresponding questions, the Fatigue Severity Scale (FSS), the MS-related symptom checklist and the Perceived Deficit Questionnaire (PDQ) were included. Data were analysed in relation to data level using Chi-square, Mann Whitney U-test, and Student's t-test. Pearson's and Spearman's correlations were calculated. In the logistic regression analyses (enter) dichotomized MS-symptoms were used as dependent variables, and EDSS, disease-course, time since onset, heat-sensitivity, age and sex (female/male) were independent variables. In the linear regression analyses, enter, mean FSS and summarized PDQ were entered as dependent variables and EDSS, disease-course, time since onset, heat sensitivity, age and sex (female/male) were independent variables.

RESULTS

Of the responding patients (n = 256), 58% reported heat sensitivity. The regression analyses revealed heat sensitivity as a significant factor relating not only to fatigue (p < 0.001), but also to several other common MS symptoms such as pain (p < 0.001), concentration difficulties (p < 0.001), and urination urgency (p = 0.009).

CONCLUSIONS

Heat sensitivity in MS patients is a key symptom that is highly correlated with disabling symptoms such as fatigue, pain, concentration difficulty and urination urgency.

Thermoregulation in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurological disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurological symptoms with heat exposure. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. This review focuses on five main themes regarding the current understanding of thermoregulatory dysfunction in MS: 1) heat sensitivity; 2) central regulation of body temperature; 3) thermoregulatory effector responses; 4) heat-induced fatigue; and 5) countermeasures to improve or maintain function during thermal stress. Heat sensitivity in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block, which can be quantitatively characterized using precise measurements of ocular movements. MS lesions can also occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Fatigue during thermal stress is common in MS and results in decreased motor function and increased symptomatology likely due to impairments in central conduction. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacological) for the MS patient to preserve function and decrease symptom worsening during heat stress.