Mechanically evoked itch in humans.

When a newly developed experimental method to vibrate vellus hairs on human skin was applied to the face and arm in healthy subjects, intense itch was reproducibly induced on the face, but not on the arm, without any flare reactions. In contrast to histamine-induced itch, mechanically evoked itch was not characterized as burning or stinging by any subjects, and was resistant to histamine H1-receptor antagonists. When the stimulation was continued for 10 min, mechanically evoked itch reached the maximum intensity within 10 s, but gradually attenuated after 60 to 90 s and was rarely perceivable at the end of stimulation. When the stimulation was discontinued at 90 s, mechanically evoked itch rapidly attenuated after the end of stimulation, but took more than 10 min before it completely diminished. These results indicate a possible involvement of C-tactile neurons in mechanically evoked itch because they have consistent characteristics such as low mechanical thresholds, intermediate adaptation, after discharge, favorable response to slowly moving stimuli, and fatigue during repeated mechanical stimulation, although it needs to be confirmed by future microneurographic studies. Touch-alloknesis was present in the adjacent skin area until mechanically evoked itch completely diminished, supporting the hypothesis that itch sensitization can be caused by a continuous activation of peripheral itch neurons whether or not they are histamine-sensitive C nerves. In conclusion, this study provides direct evidence of mechanosensitive nerves involved in itch in human skin. The purity of mechanically evoked itch without any pain-related sensory components is a major advantage for investigating the differentiation of itch from pain.

Effects of bepotastine and fexofenadine on histamine-induced flare, wheal and itch.

BACKGROUND: Urticaria is mainly caused by mast cell-derived histamine through the histamine H(1) receptor. Antihistamines are occasionally used on demand upon a recurrence of urticaria; therefore, rapidly acting agents should be explored. The onset of action is assumed to depend on time to maximum concentration (T(max)), but the speed of action needs to be evaluated not only through blood concentration analysis but also by measuring in vivo effectiveness. METHODS: In this study, we chose two representative second-generation antihistamines (bepotastine and fexofenadine) with relatively short T(max) values and evaluated their effects on histamine-induced skin responses using both visual and laser Doppler imaging scales. RESULTS: Suppression of histamine-induced flare and itch was observed 3 and 6 h after administration of both antihistamines. Attenuation of itch was seen 30 min after the administration of each drug and thereafter until 6 h. In addition, bepotastine suppressed flare formation after only 30 min following application. CONCLUSION: These results suggest that antihistamines suppress histamine-induced itch and flare, followed by wheal formation, and that bepotastine suppresses skin symptoms sooner after administration than fexofenadine does, which is relatively consistent with the T(max) results.

Cerebral representation of the relief of itch by scratching.

Cerebral processing of itch-scratching cycles was studied with functional magnetic resonance imaging (fMRI) in healthy volunteers. The back of the hand was repetitively scratched in the absence and presence of itch induced by histamine applied close to the scratched site. Blood-oxygenation-level-dependent (BOLD) effects were assessed in predefined cortical and subcortical brain regions of interest. Scratch-related activation clusters were found in cortical and subcortical areas which had been associated before with pain processing, namely S1, S2, parietal association cortex, motor and premotor cortex, anterior and posterior insula, anterior and medial cingulum, lateral and medial frontal areas, ipsilateral cerebellum and contralateral putamen. Cortical activations were generally stronger in the contralateral hemisphere. General linear model (GLM) analysis and GLM contrast analysis revealed stronger activations during itch-related trials in the motor and premotor cortex, in lateral frontal fields of both sides, and in a left medial frontal cluster. Subcortically, stronger activation during itch-related scratching trials was found in the contralateral putamen and in the ipsilateral cerebellum. Time course analysis showed significantly higher BOLD levels during the last 3-6 s before the start of scratching when the itch intensity was strongest. This effect was found in frontal areas, in the putamen, and in the somatosensory projection areas. During the scratching, no significant differences were found between itch and control conditions with the exception of the putamen, which showed stronger activations during itch-related scratch bouts. We interpret these itch-related activations anticipating the scratching as possible cerebral correlates of the itch processing and the craving for scratch.

Primary localized cutaneous amyloidosis with unusual clinical features in a patient with Sjögren's syndrome.

A 69-year-old woman presented with a 2-year history of an eczematous lesion covering the genital area. Histopathological examination showed deposits of amorphous, eosinophilic material and an infiltrate of plasma cells through the entire dermis into the subcutaneous fatty tissue. Congo red-stained deposits showed apple-green birefringence with polarizing microscopy. On immunohistochemistry, the deposited material was positively stained with anti-lambda light chain antibodies but not with anti-lambda light chain. A diagnosis of primary localized cutaneous amyloidosis (PLCA) was made, and the patient was also diagnosed as having Sjögren's syndrome (SjS) based on clinical and laboratory findings. The lesion of PLCA has spontaneously regressed over a period of 18 months. We report a unique case of PLCA and SjS that clinically demonstrated genital eczematous features and spontaneous involution, and we also describe a possible association between PLCA and SjS.