Assessment of cutaneous parameters and sympathetic skin response as a non-invasive complementary diagnostic tool in psoriasis: An exploratory study

   Abstract 


Background: Various diagnostic tools are used to assess cutaneous psoriasis, but most of it were subjective. Sympathetic skin response (SSR), skin PH and temperature objectively measure the skin barrier functions that could aid clinicians to evaluate accurately and predict skin disease incidence even before the onset of clinical symptoms. Aim and Objectives: The study's objective was to assess the utility of cutaneous parameters (skin temperature and pH) and SSRs influencing psoriatic patients' diagnosis management and treatment compared to controls. Materials and Methods: A total of 40 healthy participants and 40 psoriasis patients aged 18 to 65 years were recruited for this study. SSR, skin temperature and pH were assessed. The psoriasis disability index (PDI) was recorded from all the patients. Data analysis was carried out using SPSS version 20.0. Results: The results shows significantly increased skin temperature, prolonged SSR latency (bilaterally) and decreased SSR amplitude (bilaterally) among patients affected with psoriasis compared to control subjects. There is a positive correlation between SSR latency with PDI and a negative correlation between SSR amplitude and PDI in psoriasis patients. Conclusion: SSR reveals sympathetic sudomotor dysfunction and increased skin temperature in psoriasis. Furthermore, there is a link between increased SSR latency and PDI, which shows that local nervous system impairment significantly contributes to the inflammatory process in psoriasis. Thus, SSR can be used as a complementary tool for the early identification and assessment of epidermal barrier integrity in psoriasis patients, along with the clinician's standard protocols.

Keywords: Psoriasis, skin pH, skin temperature, sympathetic skin response


How to cite this article:
Sundareswaran L, Nagendran P, Subramanian SK, Dharmalingam A, Mohuiddin SG. Assessment of cutaneous parameters and sympathetic skin response as a non-invasive complementary diagnostic tool in psoriasis: An exploratory study. Indian J Dermatol 2023;68:195-9
How to cite this URL:
Sundareswaran L, Nagendran P, Subramanian SK, Dharmalingam A, Mohuiddin SG. Assessment of cutaneous parameters and sympathetic skin response as a non-invasive complementary diagnostic tool in psoriasis: An exploratory study. Indian J Dermatol [serial online] 2023 [cited 2023 Apr 28];68:195-9. Available from: 
https://www.e-ijd.org/text.asp?2023/68/2/195/375222    Introduction Top

The sympathetic skin response (SSR) recording is one of the non-invasive studies to assess the sympathetic nervous system. It correlates well with other autonomic function tests in various neurologic disorders such as diabetic neuropathy.[1],[2] SSR is explored on various skin disorders related to nervous system abnormality, including leprosy, scleroderma and palmoplantar hyperhidrosis.[1] A change in skin electrical potential caused by the activation of sudomotor unmyelinated sympathetic efferent fibers, which may occur spontaneously or reflexively in response to a variety of internally or externally applied physiological or psychological stimuli, is recorded as SSR.[3] Changes in skin impedance[4] owing to ion transport across skin sweat gland cell membranes, are indicative of this possible response.[5] Changes in SSR were associated with skin hydration or moisture content. Therefore, the characteristics of SSR could be used to assist the skin disorder diagnoses relatively early[6] and to identify their stages and guide treatment.

Psoriasis is an immune-mediated, papulosquamous dermatosis associated with pruritus that affects the quality of life of more than millions worldwide. The morphological types of psoriasis are psoriasis Vulgaris (Chronic stable plaque-type), guttate psoriasis, pustular psoriasis and erythrodermic psoriasis; we have considered only chronic stable plaque-type psoriasis, characterised by multiple well-defined silvery white micaceous scaly erythematous plaques predominantly affecting the scalp, extensors and lower back. To date, only management of symptoms with poor compliance of treatment to disease is available with no complete cure.[7] Traditionally, the severity and efficacy of psoriasis treatment are visually assessed by clinicians using various subjective parameters, such as erythema, scaling and infiltration. However, such methods are subjective, and the results can vary among investigators. Hence, diagnosing the disease at an earlier stage is imperative to begin treatment and to grade the severity objectively. Various non-invasive methods, such as changes in skin capacitance, skin conductance, trans-epidermal water and skin pH, are being explored for the same.[8],[9] The skin capacitance and trans-epidermal water loss exhibited a good correlation with the visual evaluation of skin dryness, but the skin conductance did not.[9]

Emerging evidence in the literature states that stress and psoriasis are highly related. The most common trigger for flaring in psoriasis is emotional stress.[10],[11] Sympathetic skin nerve activity is an indicator of sympathetic function and is also associated with emotional responses.[12] Studying the SSR in psoriasis patients also may provide preliminary information to the clinicians about the patient's brain–skin axis, the basis of local neuroimmunoendocrine circuitry toward the underlying cause and pathogenesis of allergic and inflammatory skin diseases triggered or aggravated by stress.[13]

With this background, the study was designed to assess and compare SSR, skin pH and skin temperature in patients affected with psoriasis with age and gender-matched control groups.

   Materials and Methods Top

The present study was carried out in the autonomic function lab, department of Physiology, at the All India Institute of Medical Sciences, Mangalagiri, Andhra Pradesh, India. This study was initiated after the approval of the institutional ethical committee (AIIMS/MG/IEC/2021-21/12). This study protocol was explained in detail to the patients attending the Dermatology clinic of AIIMS Mangalagiri, India, and informed written consent was obtained. The inclusion criteria are as follows: established clinical diagnosis of mild to moderate chronic stable plaque-type psoriasis patients who attended the Dermatology clinic.

Only patients willing to volunteer for this study of both genders between the age group of 18 and 65 years were allowed to enroll. Before the study initiation, a detailed medical history and medical examination were carried out, and 80 patients were randomly allocated (40 controls and 40 psoriasis patients) after the inclusion and exclusion criteria (alcoholics, smokers, diabetes and hypertensive patients consuming drugs or undergoing therapies for any other diseases). No reported or possible side effects were involved or reported in this study, and they were in regular follow-ups.

For skin pH measurement, it was recorded from the skin surface using the glass electrode technique. The meter was calibrated 30 min before measurements using standard buffers at pH 8.0 and 2.0. The measurement was conducted by placing the moistened pH electrode in the forearm, between the wrist and elbow. The electrode will be placed on the skin for 30 s, and an average of three readings will be taken.[14] The electrode was washed with distilled water before the measurement and every time between the readings. Before the recordings, the patients were asked to wash their hands with ordinary tap water and instructed to sit in the lab at an ambient temperature (20–22°C) and relative humidity (40–60%) to avoid the errors caused by temperature changes and sweating on pH. Also, they were instructed not to use any tropical or oil ointments before the day of the test.

Skin temperature: It was measured in degrees Celsius. The recording was done in the same room with a similar setup for pH. The temperature was measured from the skin surface of the areas with less lesionss or unaffected areas near the lesion areas of the forearm, the area between the wrist and elbow. An average of three recordings is noted.

SSR measurement protocol: The SSR was performed in the autonomic lab with an ambient temperature of 22°C to 24°C in a semi-darkened room. SSR was recorded using two-channel electrodes (Aleron 201, Recorders and Medicare systems Pvt Ltd, India) described by[15] (Aleron 201, Recorders and Medicare systems Pvt Ltd, India) to record SSR. Standard surface disc electrodes were used. Active electrodes were placed on the palmar side, and reference electrodes were placed on the dorsal side of both hands and secured using micropore plaster. After placing the electrodes, the subject was allowed 15 min of rest in the supine position. To evoke the SSR, the median nerve was stimulated at the wrist with a single square wave pulse of 0.1 ms duration at irregular periods with a minimum interval of 30 s between the stimuli to avoid habituation. The current strength was gradually increased until a clear response was obtained. Sensitivity was set at 500 V/div and time at 500 ms/div. The low-frequency filter was set at 0.2 Hz and the high-frequency filter at 500 Hz. At least 10 responses were recorded, and the response with the shortest latency was selected. The SSR was considered absent if no response was obtained after 10 trials performed on three occasions using a maximum current of 60 mA. The latency was measured from the onset of the stimulus artifact to the onset of the response, and peak-to-peak amplitudes were noted. From the tracings, SSR (latency and amplitude) will be calculated according to the standard guidelines.[16]

The subjects and psoriasis patients were asked to refrain from any drugs or any vasomotor substance (e.g., alcohol, coffee, tea, etc.) nor undergo any strenuous physical activity minimum of 2 h before evaluation on the day of the test. The same criteria and protocol were followed for the control subjects, and recording was done in the same setup. Psoriasis Disability Index (PDI) questionnaire contains 15 psoriasis-specific questions under the five headings: daily activities, work, personal relations, leisure and treatment to analyse the psoriasis disability associated with psoriasis.[17],[18]

Statistical Analysis: Data will be analysed using SPSS software package version 20.0 (SPSS Inc., Chicago, USA). Statistical significance between the different groups was determined by independent student T-test, and the significance level was fixed at P < 0.05.

   Results Top

Groups with age group; control group 44.35 ± 10.84 and psoriasis group 46.42 ± 11.25; P value = 0.818) and gender (control n = 40, Male/Female – 34/6; Study group n = 40 Male/Female – 37/3, P value = 0.762).

Sympathetic skin response: [Table 1] compares SSR latency and amplitude and skin pH and temperature between the control and study groups. SSR latency was significantly higher, and SSR amplitude was significantly lower in the Psoriasis group [Figure 1] and [Figure 2]. Skin temperature was significantly higher in the psoriasis group, while skin pH was similar.

Figure 1: Sympathetic skin response recording of N- type in psoriasis patients with amplitude and latency values

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Figure 2: Sympathetic skin response recording of P-type in healthy control subjects with amplitude and latency values

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PDI scores: [Table 2] PDI scoring: It is to be noted that the majority of the psoriasis patients have greater PDI scores.

[Figure A] shows that PDI scores significantly positively correlate with SSR latency (r = .598, P < .001). PDI scores could explain 32% of the variance in SSR latency (based on the R2 value). [Figure B] shows that PDI scores are significantly negatively correlated with SSR amplitude (r = -.419, P = .007). PDI scores could explain 17% of the variance in SSR latency (based on the R2 value).

   Discussion Top

To date, the precise cause of psoriasis remains unclear, which makes the treatment challenging. The cause is chiefly attributed to Th1-mediated autoimmunity, which could be due to various reasons, including trauma, infections, medicines, genetic factors and smoking.[19],[20] However, decreased sweating in psoriasis patients might be due to ANS dysfunction. Psoriasis has been shown to alter epidermal barrier function,[21] which preserves cutaneous homeostasis and defends the body against various external stressors.[22] Skin surface pH[23] and temperature[24] are typically used to evaluate epidermal barrier function. Hence, the present study aimed to study autonomic function (using the SSR approach), skin pH and temperature among psoriasis patients.

We observed an increased skin temperature among psoriasis patients compared to the control group, with no significant changes observed in skin pH, the similar results were observed in psoriasis vulgaris patients with plagues combined with balenotherapy.[25] This study's findings suggest that increased temperature in psoriatic skin with no change in skin pH could be due to a compromised epidermal barrier in psoriatic patients, not just the psoriatic plaques[26] or it could be due to the inflammatory process.[27]

Inflammatory mediators such as TNF- alpha, IL 1, IL 12, IL 17 and IL 23 have been implicated in the complex pathogenesis of psoriasis. Pro-inflammatory cytokines have been shown to inhibit the sympathetic nervous system at the site of inflammation in patients with psoriasis.[28] Scientific literature documented the vital role of the nervous system in the process of inflammation.[29] In support of these findings, an increased SSR latency was observed, suggestive of sympathetic sudomotor impairment in psoriasis patients compared to the control group. This study's findings are in line[30] as well as contradictory[31] with the previous studies in psoriasis patients.

Increased sympathetic sudomotor dysfunction in psoriasis, as evidenced by prolonged SSR latency, is positively linked with PDI, and SSR amplitude is negatively associated with PDI, which indicates that there could be significant involvement of sympathetic sudomotor dysfunction in the pathophysiological process of psoriasis. This further explains the link between the cutaneous inflammatory process and the autonomic and sensory nerves involvement leads to skin inflammation that may consequently affect the local nervous system.[30]

The observed temperature changes could be due to impaired local temperature regulation[32] Further a study states that even if the skin may appear normal or asymptomatic, the psoriasis-associated chronic immune response can be present.[33] Hence, considering only the skin lesions for diagnosis might delay the patient's diagnosis and treatment. Hence, the rapid and non-invasive parameters such as skin temperature, pH and SSR can be considered along with the routine protocols for psoriasis diagnosis, management and treatment by the clinicians. It necessitates the design of a new protocol with these parameters in mind, which would be the logical extension of this study in future.

   Conclusions Top

SSR reveals sympathetic sudomotor dysfunction and increased skin temperature in psoriasis. Furthermore, there is a link between increased SSR latency and PDI, which shows that local nervous system impairment significantly contributes to the inflammatory process in psoriasis. Thus, SSR and skin temperature can be used as complementary tools for the early identification and assessment of impaired epidermal barriers in psoriasis patients, along with the clinician's standard protocols.

Acknowledgements

This article also would like to extend sincere thanks to the Department of Dermatology and Physiology, AIIMS Mangalagiri, Andhra Pradesh, India, and volunteers for participation and for providing the necessary support.

Financial support and sponsorship

Self-funded.

Conflicts of interest

There are no conflicts of interest.

 

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  [Figure 1], [Figure 2]
 
 
  [Table 1], [Table 2]

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