Sweating patterns in atopic dermatitis patients

Skin neuropathy and immunomodulation in diseases

Skin is a vital barrier tissue of the body. Immune responses in the skin must be precisely controlled, which would otherwise cause severe disease conditions such as psoriasis, atopic dermatitis, or pathogenic infection. Research evidence has increasingly demonstrated the essential roles of neural innervations, i.e., sensory and sympathetic signals, in modulating skin immunity. Notably, neuropathic changes of such neural structures have been observed in skin disease conditions, implicating their direct involvement in various pathological processes. An in-depth understanding of the mechanism underlying skin neuropathy and its immunomodulatory effects could help reveal novel entry points for therapeutic interventions. Here, we summarize the neuroimmune interactions between neuropathic events and skin immunity, highlighting the current knowledge and future perspectives of this emerging research frontier.

Dry skin manifestations in Sjögren syndrome and atopic dermatitis related to aberrant sudomotor function in inflammatory allergic skin diseases

We have reported characteristic cutaneous manifestations of Sjögren syndrome (SS) with special references to autoimmune anhidrosis or hypoidrosis and related mucocutaenous manifestations in addition to annular erythema or cutaneous vasculitis. Although significance of cutaneous manifestations of SS has been gradually recognized in rheumatologists, sudomotor function has not been fully evaluated and recognized in the diagnosis of SS except for dermatologists. SS is a relatively underestimated collagen disease in contrast to SLE, systemic sclerosis, or dermatomyositis, special care should be needed not to make misdiagnosis of SS when we see the patients with common skin disease such as, drug eruption, infections skin disease or xerosis in the daily practice. In contrast to pathomechanisms of dry skin observed in SS, we recently reported that reduced sweating function and dry skin seen in atopic dermatitis (AD) are mediated by histamine or substance P, those are usually restored to normal levels after improvement of the dermatitis by topical corticosteroid ointment with or without oral anti-histamine. Therefore, xerotic skin lesions seen in SS and AD might be attributable to different pathomechanisms with similar dry skin manifestations. We recently reported that SS promotes dry skin when complicated with AD possibly due to acceleration of hypoidrosis. In this review, we would like to summarize our recent understanding of regulatory mechanism of impaired sweating function in allergic inflammatory skin diseases by introducing clinical presentations of AD/SS overlap cases as the model of hypoidrotic inflammatory skin diseases.

Sweat, the driving force behind normal skin: an emerging perspective on functional biology and regulatory mechanisms

The various symptoms associated with excessive or insufficient perspiration can significantly reduce a patient's quality of life. If a versatile and minimally invasive method could be established for returning sweat activity to normalcy, there is no question that it could be used in the treatment of many diseases that are believed to involve perspiration. For this reason, based on an understanding of the sweat-gland control function and sweat activity, it was necessary to conduct a comprehensive search for the factors that control sweating, such as the central and peripheral nerves that control sweat-gland function, the microenvironment surrounding the sweat glands, and lifestyle. We focused on the mechanism by which atopic dermatitis leads to hypohidrosis and confirmed that histamine inhibits acetylcholinergic sweating. Acetylcholine promotes the phosphorylation of glycogen synthesis kinase 3β (GSK3β) in the sweat-gland secretory cells and leads to sensible perspiration. By suppressing the phosphorylation of GSK3β, histamine inhibits the movement of sweat from the sweat-gland secretory cells through the sweat ducts, which could presumably be demonstrated by dynamic observations of the sweat glands using two-photon microscopy. It is expected that the discovery of new factors that control sweat-gland function can contribute to the treatment of diseases associated with dyshidrosis.

Four cases of atopic dermatitis complicated by Sjögren's syndrome: link between dry skin and autoimmune anhidrosis

We report four adult cases of atopic dermatitis (AD) complicated by Sjögren's syndrome (SS). The patients fulfilled diagnostic criteria for AD and SS. All cases showed persistent itchy dry skin and eczematous lesions complicated by sicca symptoms including dry eyes and dry mouth with moderate joint pain. One case manifested annular erythema and another manifested widespread discoid erythema. To investigate the underlying cause of dry skin in these cases, sweating function was evaluated using a quantitative sudomotor axon reflex test (QSART) in which the axon reflex is stimulated by acetylcholine iontophoresis. The sweating latency time was significantly prolonged in eczematous skin of AD and AD/SS compared to normal controls. Axon reflex (AXR) sweat volume was also significantly reduced in AD (normal and eczematous skin) and AD/SS (normal and eczema) compared to normal control. In contrast, the direct sweat volume of lesional or non-lesional AD skin induced by direct stimulation with acetylcholine was only slightly reduced compared to that in normal controls, but not in SS and lesional skin of AD/SS patients. These results suggest that the impaired sweat response in AD is attributable to an abnormal sudomotor axon reflex, which is accelerated and modulated when complicated by SS resulting in dry skin in the present cases.

Mechanisms and controllers of eccrine sweating in humans

Human body temperature is regulated within a very narrow range. When exposed to hyperthermic conditions, via environmental factors and/or increased metabolism, heat dissipation becomes vital for survival. In humans, the primary mechanism of heat dissipation, particularly when ambient temperature is higher than skin temperature, is evaporative heat loss secondary to sweat secretion from eccrine glands. While the primary controller of sweating is the integration between internal and skin temperatures, a number of non-thermal factors modulate the sweating response. In addition to summarizing the current understanding of the neural pathways from the brain to the sweat gland, as well as responses at the sweat gland, this review will highlight findings pertaining to studies of proposed non-thermal modifiers of sweating, namely, exercise, baroreceptor loading state, and body fluid status. Information from these studies not only provides important insight pertaining to the basic mechanisms of sweating, but also perhaps could be useful towards a greater understanding of potential mechanisms and consequences of disease states as well as aging in altering sweating responses and thus temperature regulation.

A new wrinkle: skin manifestations of aging may relate to autonomic dysfunction

Various mechanisms have been argued for skin wrinkling, one of the hallmarks of aging. We hypothesize that chronic sympathetic bias is a previously unrecognized mechanism for wrinkling. In the acute setting of water immersion, reversible skin wrinkling is a well-known reflex mediated by the autonomic nervous system. We postulate that skin wrinkling results as a local maladaptive manifestation of a global chronic sympathetic bias that emerges during aging. The persistence of such changes may induce additional compensatory remodeling to cause permanent alteration of the skin. Sympatholytic agents may prove beneficial for arresting or ameliorating the development of wrinkles. Conditions that amplify sympathetic bias such as stress, smoking, amphetamine abuse, HIV, heart failure, and transplantation may accelerate wrinkling. Other common diseases of the skin may also arise as particular manifestations of aberrant autonomic activity through induction of vascular and immune dysfunctions. The temporal and spatial distribution of these dermatologic conditions may reflect variation of autonomic balance, which also regulates T helper immune balance. For all of these dermatologic conditions, local and systemic administration of drugs and medical devices that pharmacologically or electrically modulate autonomic nervous system activity may yield benefits as well.

Impaired sweating function in adult atopic dermatitis: results of the quantitative sudomotor axon reflex test

BACKGROUND

Impaired sweating is thought to be a cause of barrier dysfunction in atopic dermatitis (AD).

OBJECTIVES

To examine the sweating function in AD in a quantitative manner.

METHODS

We investigated the sweating response of lesional and non-lesional skin of adult patients with AD by a quantitative sudomotor axon reflex test in which the axon reflex is stimulated by acetylcholine iontophoresis. Sweat volume on the volar aspect of the forearm was measured in 18 adult patients with AD and in 40 non-atopic controls; five patients with Sjögren's syndrome were also studied as disease comparators. We also evaluated the sweating function in four AD patients after topical corticosteroid therapy. Latency time, direct (DIR) sweat volume and axon reflex-mediated indirect (AXR) sweat volume were the variables studied.

RESULTS

The latency time in AD patients was significantly prolonged and AXR sweat volume significantly reduced compared with those in non-atopic control subjects. The latency time and AXR sweat volume of lesional AD skin were significantly more prolonged and reduced, respectively, than those of non-lesional skin. In contrast, the DIR sweat volume of lesional or non-lesional AD skin induced by direct stimulation with acetylcholine was only slightly reduced when compared with that in non-atopic controls. Latency time and sweat volumes of lesional and non-lesional AD skin improved after topical corticosteroid therapy.

CONCLUSIONS

These results suggest that the impaired sweat response in AD is attributable to an abnormal sudomotor axon reflex, which is reversed by topical corticosteroid administration.

Do training-dependent differences in perspiration exist between healthy and atopic subjects?

Sweating (perspiratio sensibilis) serves predominantly for thermoregulation and is triggered, among other stimuli, by physical stress. Although consensus on sex-dependent differences in sweating has not been reached so far and recent studies revealing abnormal diminution of the sweating capacity in atopic subjects are mainly based on heat exposure experiments, the influence of endurance training on perspiration in atopics has not yet been evaluated. Using a special sweat collector device reliable even during intensive body movement, we compared the sweat production of age-matched male and female healthy controls (14 m, 10 f) to that of in-patients with atopic eczema (AE: 14 m, 10 f) during and 5 min after physical exercise (30 min) with a bicycle ergometer under standardized experimental conditions. The individual stress limit was determined by a previous endurance test including repeated lactate blood level measurements and continuous heart rate control. Informed consent was obtained from every participant in the study. One half of both the patients and the controls underwent three week endurance training, and the preceding sweat measurements were repeated in all patients and controls after the training period under identical conditions. On average, the healthy males perspired nearly twice as much as the corresponding females (p < 0.0016). Highly significant mean differences of maximum sweat secretion rates were also found between the atopics and the controls. Healthy individuals of both sexes perspired nearly three times as much as did the patients with AE (males: p < 0.0004; females: p < 0.00009). Among the atopics there were remarkable, yet statistically insignificant, sexual differences in sweat production. After three weeks, sweating rates were similar to the initial ones in the training group as well as in the non-trained control group. Gender differences in perspiration do not only exist between healthy males and females but also in patients with atopic skin disorder, yet the latter ones at significantly lower levels as compared to healthy control subjects. No influence of a three-week-exercise phase on sweat secretion in atopics and controls could be proven. For designing further studies on intra- or intersexual differences of drug-independent perspiration, standardized physical stress can be recommended as an experimental prerequisite for sweat measurements.

Quantitative sudomotor axon reflex test (QSART): a new approach for testing distal sites

The quantitative sudomotor axon reflex test (QSART) is a useful tool in the evaluation of C-fiber function. Because many neuropathies show a length-dependent loss of nerve function, a new capsule was designed for distal performance of the QSART, allowing measurements on fingers and toes. We investigated 20 healthy volunteers and 15 patients with insulin-dependent diabetes mellitus and normal sensory nerve conduction studies. A QSART was performed on the forearm and on the thumb. The groups showed no differences in the QSARTs on the forearm, but the sweat volume on the thumb was significantly lower in patients. Calculation of the forearm/finger ratio reduced the interindividual variation and showed the highest sensitivity for detecting C-fiber dysfunction in the patient group. We conclude that the distal measuring device and the forearm/finger ratio are more sensitive tools for the early detection of distal-onset neuropathies than are the commonly used proximal testing sites.

Pilocarpine-induced cholinergic sweat secretion compared with emotional sweat secretion in atopic dermatitis

We studied pilocarpine-induced cholinergic sweating, emotional sweating and sympathetic reflex sweating in atopic dermatitis (AD) patients. Secreted sweat was measured both with equipment that continuously records sweat rate and with a filter paper method that measures sweat weight absorbed. Comparison of the two methods revealed that the filter paper method underestimated the sweat secretion in AD patients. While AD patients showed no significant abnormalities in emotional sweating and sympathetic reflex sweating, the duration of pilocarpine-induced sweating was prolonged. The time from the maximal sweat rate until the sweat rate fell to half of the maximal rate was significantly longer in AD patients than in control subjects. In contrast, the time from the beginning of sweat secretion until the maximal sweat rate was not significantly different between AD patients and control subjects. There was no significant difference between AD patients and control subjects in sweat volume secreted in 20 min after pilocarpine iontophoresis. In AD patients, the total sweat volume secreted after pilocarpine iontophoresis was greater than in control subjects, although not significantly. These results suggest that the system of deactivation of pilocarpine-induced sweat secretion is impaired in AD patients whereas the activation system is not altered.

Thermal and sweating responses in normal and atopic subjects under internal and moderate external heat stress

To compare the thermoregulatory responses of normal subjects and patients with atopic dermatitis, the effect of exercise under moderate heat stress was examined in two groups of subjects. Each group of eight subjects (controls or clinical atopics) underwent a 90-min experiment after being equipped with probes for measurement of core and skin temperatures, heart rate and overall and local sweating rates. Sweat surface tension was determined from sweat collection made at the end of the session. The experimental procedure was as follows: 30 min rest at thermoneutrality, 30 min cycling at 90 W at 36 degrees C, followed by 30 min recovery sitting at rest at 36 degrees C on the cycloergometer. None of the registered variables differed significantly between the normal and atopic subjects except for variations in mean skin temperature, core-to-skin temperature difference and sweat surface tension. Since local sweating on non-affected skin under a controlled thermal clamp was not altered by atopy, it can be concluded that the thermoregulatory modifications under heat stress is of vasomotor origin, the benefit of which, in terms of heat dissipation capacity, remains uncertain. There may be alterations in the constituents of sweat, but not in its excretion rate. Local, rather than central, factors are probably involved in this qualitative change, which remains to be investigated.

Sweating response to moderate thermal stress in atopic dermatitis

The local sweating response to thermal stress (mean ambient temperature 33 degrees C) was assessed under resting conditions on the non-eczematous back skin of 26 young men with atopic dermatitis (AD) and in 22 non-atopic controls with other dermatoses. The baseline (transepidermal) water loss was separately determined at room temperature (mean 23.6 degrees C) to calculate the pure sweat loss. A gravimetric collecting method was used for the measurements at 40, 60 and 80 min. In the heated room the sweat loss in AD patients was significantly lower at all time intervals. The cumulative sweat loss was 50-60% lower in AD patients than in the controls (P less than 0.02). Subjects with dry AD skin had a lower sweat loss than subjects with normal-looking skin. Compared with controls the sweat loss in AD patients was lowest at 40 min, suggesting a retarded sweating response. Half of the patients with AD and half of the controls had active participation in sports, and showed a greater sweat loss compared to the non-sporting subjects in the same group.

Baseline water loss and cholinergic sweat stimulation in atopic dermatitis: a gravimetric measurement of local skin water loss

The sweat gland function in atopic dermatitis (AD) and in respiratory atopy is a matter of controversy. We examined the baseline water loss and local sweating response in non-eczematous back skin of 146 young men: pure AD, AD with rhinitis/asthma, rhinitis/asthma alone, non-atopic dermatosis and non-atopic healthy. All AD subjects were further divided into the subgroups AD dry and AD normal skin. Following injections of saline and a high concentration of methacholine (5 x 10(4) mol/l) into separate sites the moisture losses were collected into closed pads over a period of 40 min. The baseline water loss was significantly increased (P less than 0.001) and median pure sweat loss was significantly decreased (P less than 0.01) in AD compared with nonatopic healthy individuals. These trends were accentuated in AD dry skin. Respiratory symptoms had no appreciable influence on results. A depressed sweating response occurred in 30% of AD subjects and 9% of non-AD subjects. An elevated baseline water loss value and a depressed sweat loss value coexisted in 22% of subjects with AD dry skin compared with 3% of the non-atopics.