Central centrifugal cicatricial alopecia severity is associated with cowhage-induced itch.

BACKGROUND: Patients with central centrifugal cicatricial alopecia (CCCA) often suffer from varying degrees of itch, pain and burning sensations. However, the neural component of these skin sensations has not been assessed. OBJECTIVE: To conduct a comprehensive analysis of C nerve fibre function relating to itch and pain perception in patients with CCCA using thermosensory testing and experimental itch models. METHODS: Fifteen healthy African-American women and 16 African-American female patients with CCCA participated in the study and underwent quantitative computerized thermosensory testing to assess warmth and heat pain thresholds. Itch was induced using histamine iontophoresis and application of cowhage spicules, and the intensity of each itch was assessed. The association between itch intensity and CCCA severity score was examined. RESULTS: A positive correlation between CCCA severity score and peak itch ratings of cowhage on the lesional scalp (crown) was observed (P = 0·023, r = 0·562). Notably, the histamine peak itch rating was not found to have a significant correlation with CCCA severity score (P = 0·913). The crown also had significantly higher warmth and pain thresholds than the occiput in both healthy subjects and patients with CCCA. CONCLUSIONS: Our results suggest a putative role for the protease-activated receptor (PAR)-2, which is activated by cowhage, in the pathogenesis of CCCA. Future studies should examine PAR-2-directed therapeutics for patients with CCCA. Examining for itch and other dysaesthesias in patients with CCCA is of vital importance to dermatologists in assessing disease severity.

Aberrant C nerve fibre function of the healthy scalp.

BACKGROUND: The scalp is commonly associated with itch and burning sensations. Previous studies have shown the scalp is highly innervated compared with other body areas. However, limited data are available on sensory testing associated with C nerve fibres of the healthy scalp. OBJECTIVE: To examine the function of C nerve fibre-mediated sensations such as warmth, heat pain, itch and neurogenic inflammation in two areas of the scalp (crown and occiput) in comparison to forearm skin. METHODS: Twenty-two healthy subjects (11 women, 11 men) underwent quantitative computerized thermosensory testing to assess warmth and heat pain thresholds. Itch was induced using histamine iontophoresis and application of cowhage spicules, and the intensity of each itch was assessed. Skin blood flow was measured at baseline and after each itch induction to assess degree of neurogenic inflammation. RESULTS: A majority (64%) of the crown warmth threshold measurements exceeded 50°C while all 22 forearm warmth thresholds measurements were significantly lower than 50°C. Both scalp sites had significantly higher warmth and heat pain thresholds compared with the forearm (P<0·001). Itch ratings of histamine and cowhage on both scalp sites were significantly lower than on the forearm (P≤0·001). Histamine and cowhage induced an increase in skin blood flow from baseline on the forearm compared with the scalp (P< 0·001). CONCLUSIONS: This study demonstrates a significant insensitivity of C nerve fibres of the scalp to warmth, heat pain, itch and neurogenic inflammation. These results suggest that the scalp has an aberrant response of C nerve fibres.

The pleasurability of scratching an itch: a psychophysical and topographical assessment.

BACKGROUND: Scratching an itch is perceived as being pleasurable. However, an analysis of topographical variations in itch intensity, the effectiveness of scratching to provide itch relief and the associated pleasurability has not been performed at different body sites. OBJECTIVES: To examine the role of scratching pleasurability in providing itch relief by investigating whether itch intensity is perceived differently at three different sites and to assess a potential correlation between the pleasurability and itch attenuation induced by scratching. METHODS: Itch was induced on the forearm, ankle and back using cowhage spicules in 18 healthy subjects. These sites were subsequently scratched by an investigator with a cytology brush immediately following itch induction. The intensity of itch with and without scratching at these sites and the pleasurability of scratching were recorded by taking visual analogue scale ratings at 30-s intervals. RESULTS: Mean itch intensity and scratching pleasurability ratings at the ankle and back were significantly higher than on the forearm. For the forearm and ankle, the greater the itch while scratching, the higher was the pleasurability. A higher baseline itch was linked to a higher itch reduction secondary to scratching in all tested areas. Pleasurability paralleled the curve of itch reduction for the back and forearm; however, scratching pleasurability at the ankle remained elevated and only slightly decreased while itch was diminishing. CONCLUSIONS: There are topographical differences in itch intensity, the effectiveness of scratching in relieving itch and the associated pleasurability. Experimental itch induced by cowhage was more intensely perceived at the ankle, while scratching attenuated itch most effectively on the back.