Characterization of cowhage-induced pruritus in inflamed and non-inflamed skin

Cowhage-induced itch scores and the current perception threshold in assessing sensitive skin: An observational laboratory study

BACKGROUND

The diagnosis of sensitive skin remains nonuniform, and the underlying mechanism is unclear. Previous studies were inconsistent in the current perception threshold (CPT) measurement for sensitive skin; thus, the neural sensitivity of sensitive skin needs to be clarified.

OBJECTIVES

This study aimed to compare the CPT measurement and the cowhage test for sensitive skin and to investigate the correlation between CPT values and cowhage-itch scores.

METHODS

Participants with and without sensitive skin (n = 30, 30) were included. The cowhage test and CPT measurement with its related sensations were performed.

RESULTS

No difference was found in CPT between the sensitive and nonsensitive groups at either the site of the face or the forearm (5, 250, or 2000 Hz). Once the CPT was reached, sensations (itch, stinging, and throbbing) were significantly different between the two groups. Cowhage provoked more intense itch with a longer duration in the face (visual analog scale [VAS] score 1.90 ± 1.47 vs. 0.52 ± 0.90, p < 0.001; duration 3.80 ± 3.31 vs. 0.87 ± 1.43 min, p < 0.001) and forearm (VAS 2.53 ± 2.60 vs. 0.72 ± 1.06, p < 0.001; duration 3.37 ± 3.46 vs. 1.33 ± 2.14 min, p < 0.01) of the sensitive group compared with the nonsensitive group. Cowhage-induced itch and CPT-related itch (5 Hz) showed moderate correlations in both the face (r = 0.441, p < 0.001) and forearm (r = 0.491 p < 0.001) and weak correlations in the forearm (r = 0.323 at 250 Hz, p = 0.012; r = 0.376 at 2000 Hz, p = 0.003).

CONCLUSIONS

Cowhage test showed better performance in assessing the neural sensitivity of sensitive skin in comparison with the CPT measurement. Evaluation of CPT-related sensations may add valuable information to sensitive skin assessment.

Characteristics of pruritus in various clinical variants of psoriasis: Final report of the binational, multicentre, cross-sectional study

BACKGROUND

Pruritus, which is the most frequent subjective symptom of psoriasis, may cause significant discomfort, embarrassment and even interfere with patients normal daily activities. However, the perception of itch in various psoriasis subtypes remains unknown.

OBJECTIVES

The aim of this study was to investigate and to characterize pruritus in different clinical variants of psoriasis.

METHODS

This cross-sectional, binational, multicentre study included 295 subjects suffering from nine different clinical subtypes of psoriasis: large-plaque psoriasis (n = 45), nummular psoriasis (n = 32), guttate psoriasis (n = 31), scalp psoriasis (n = 32), inverse psoriasis (n = 23), erythrodermic psoriasis (n = 33), palmoplantar psoriasis vulgaris (n = 33), palmoplantar pustular psoriasis (n = 42) and generalized pustular psoriasis (n = 23). Measures included sociodemographic and anthropometric data, detailed pruritus characteristics including but not limited to pruritus intensity, frequency and extend, as well as psoriasis severity.

RESULTS

The lifetime prevalence of pruritus in each clinical variant of psoriasis was similar and quite high, reaching up to 100% in some disease subtypes (i.e., nummular psoriasis, scalp psoriasis and generalized pustular psoriasis). Psoriasis severity correlated with pruritus intensity in scalp psoriasis, palmoplantar pustular psoriasis and generalized pustular psoriasis. The age, duration of psoriasis and BMI did not interfere with the intensity of itch.

CONCLUSIONS

Pruritus is highly prevalent in each clinical variant of psoriasis. However, the sensation of itch is very individual, difficult to universally describe even in the same subtype.

Characterization of Cowhage-induced Pruritus in Sensitive Skin: An Observational Laboratory Study

Sensitive skin is a prevalent syndrome, characterized by discomfort in response to mild stimuli, which impacts on quality of life. Pruritus is one of the major symptoms of sensitive skin. However, the pathomechanism of sensitive skin is insufficiently understood. As an experimental model for pruritus, the cowhage skin prick test might provide insight into the understanding of sensitive skin. This study aimed to specify the characteristics of cowhage-induced pruritus in sensitive skin. Female volunteers, 20 with sensitive skin and 20 controls, were recruited. Self-report questionnaires were distributed and the responses evaluated; moreover, alongside assessments by dermatologists, skin physiology assessments, lactic acid sting test, capsaicin test and cowhage skin challenge were performed. Pruritus in sensitive skin was perceived as more intense and longer-lasting than in normal skin, with different qualities of accompanying sensations. Cowhage skin challenge results showed moderate consistency with clinical assessments. The results suggest that cowhage skin challenge could be a new tool for the assessment of sensitive skin.

Flare Size but Not Intensity Reflects Histamine-Induced Itch

INTRODUCTION

Flare reactions arise due to the release of vasodilators from sensory nerves caused by antidromic transmission of action potentials after the induction of itch.

OBJECTIVE

We investigated the link between flare and itch using 3 models of itch.

METHODS

Skin provocations with histamine, capsaicin, and cowhage were performed in 31 subjects. Itch was quantified using the visual analog scale. Flare was assessed using laser speckle contrast imaging (LSCI) and digital photography.

RESULTS

The duration, intensity, and area under the curve of histamine-induced itch correlated with the area of increased blood flow measured with LSCI (r = 0.545, p = 0.002; r = 0.575, p = 0.001; and r = 0.649, p < 0.001, respectively). Itch and skin blood flow in response to capsaicin or cowhage did not correlate.

CONCLUSION

In histamine-induced skin inflammation, itch and increased blood flow are linked. Thus, the area of histamine-induced flare may be used as a surrogate marker for histamine-induced itch.