Itch and brain

Itch is an unpleasant somatic sensation that evokes the urge to scratch. Chronic itch is a severe problem that diminishes quality of life. There are many patients suffering from chronic itch across the world. The brain is the final terminal to receive itch‐related signals from the body and plays an important role in perceiving the itch sensation. Thus, to understand the cerebral mechanism of itch perception and how this mechanism differs between healthy subjects and chronic itch patients is important for advancing our understanding on the pathophysiology of chronic itch. Itch is suppressed by scratching or applying painful stimuli. The pleasurable sensation evoked by scratching an itch increases the urge to scratch. Viewing others in itch or imagining the itch sensation may evoke real itch sensations and the scratching response. To understand the mechanisms responsible for these phenomena may provide useful information for the development of treatment of itch and advance our understanding of the cerebral mechanism of itch and scratch. Several functional brain imaging studies have addressed these issues and reported interesting findings. In this review article, the authors discussed the findings of previous studies and how they have advanced our understanding of the central mechanisms of itch, scratch and chronic itch.     

Itch and pain

The discovery of a specialized neuronal pathway for itch has markedly improved our understanding of itch processing under physiological conditions. However, the complex interactions of pain and itch are only partly understood. This review focuses on the neurophysiological mechanisms involved in clinical and experimental itch conditions. There is emerging evidence that similar patterns of peripheral and central sensitization occur in chronic pain and chronic itch conditions. It will be of major interest to reveal whether the underlying mechanism for sensitization in the itch and pain pathways are also similar, as this might have major implications for therapy.     

大鼠瘙痒模型中瘙痒信号的初级传入通路追踪研究

目的建立大鼠瘙痒模型,观察瘙痒信号的外周传入部位。方法大鼠颈背部皮内注射2%5-羟色胺(5-HT)建立大鼠瘙痒模型。1周后,随机挑选4只大鼠行颈背部皮内注射辣根过氧化物酶(HRP),再用神经束路追踪术(TMB法)观察大鼠颈2~5(C2~C5)背根神经节(DRG)内HRP阳性细胞的分布。结果DRG中HRP阳性细胞呈散在分布,C3 DRG中阳性细胞最多见,C4中较少,C2,C5中缺乏。结论大鼠颈背部中线区域的瘙痒信号主要通过C3 DRG传入脊髓。     

瘙痒的病理生理学和治疗进展

瘙痒的产生是一个复杂的、多因素作用的结果 ,其具体机制尚不完全清楚。近年来神经病理生理学的研究对瘙痒的临床分型和治疗产生了重要的指导作用。现对瘙痒的临床分型、神经病理生理学新发现和治疗进展作一综述。     

Itch following photochemotherapy for psoriasis

Itch was measured quantitatively as nocturnal scratch in 12 patients with psoriasis treated with 8-methoxypsoralen and UVA and in 7 treated with dithranol. Three of those treated with PUVA showed an increase in nocturnal limb movement which was mostly due to itch but partly due to restlessness. There was little change in nocturnal limb movement in patients treated with dithranol.     

Dogger Bank Itch and cyclosporin

Two cases of Dogger Bank Itch responding to oral cyclosporin (Neoral) are reported. The first, a 42-year-old shell-fisherman, presented with eczema on his face, forearms and hands. Oral prednisolone was ineffective and in subsequent years systemic steroids and topical clobetasol propionate allowed him to continue his work. In the shellfishing season of 1996, cyclosporin (Neoral) was introduced and the eczema was subsequently satisfactorily controlled. The second fisherman, aged 46, presented with an irritant eczema of the hands and forearms. Initial treatment with emollients and potent topical steroids had little effect. A subsequent course of cyclosporin provided good control of the eczema.     

Cutaneous Innervation and Itch in Keloids

Abstract is missing (Letter).     

Itch and atopic dermatitis: an overview

Itching is the hallmark of atopic dermatitis, and a vicious itch-scratch circle is easily established. Itching and scratching are important factors in the maintenance of symptoms and can have a significant impact on the sufferer's quality of life. The pathophysiology of itch in atopic dermatitis is still not understood. Unlike in urticaria, histamine is not considered to be a major pruritogen in atopic dermatitis. In fact, the peripheral pruritogens and their cellular origin(s) still remain to be identified in this disease. Various treatments are used to relieve the skin inflammation, itching, and scratching in patients with atopic dermatitis, but no specific antipruritic therapy is available. However, several nonspecific therapies can effectively break the vicious itch-scratch circle. The use of topical corticosteroids and emollients and the elimination of individual trigger factors are still first-line measures.     

Itch in systemic disease: therapeutic options

A new pathophysiologically based classification of itch is proposed, which should help the clinician adopt a rational approach to diagnosis and management of generalized itch. Focusing on neurogenic itch (itch without visible rash), common causes are reviewed and guidelines for laboratory and radiologic investigation are proposed. A stepwise approach to the management of generalized itch resulting from systemic disease is recommended. Specifically, the relative merits of broad versus narrowband ultraviolet B (UVB) are discussed and the pros and cons of doxepin, opioid antagonists, and selective serotonin reuptake inhibitors (SSRIs) such as paroxetine are considered. Attention is drawn to some novel approaches, including bright-light phototherapy and molecular adsorbent recirculating system (MARS) for selected patients with intractable itch caused by hepatic failure, and mirtazapine for nocturnal itch.     

Itch pathophysiology may differ among ethnic groups

The prevalence of itch is higher in individuals with darker skin types. In this paper, we review the systems involved in the physiology of itch and how they may differ across the races. Current data point out that the differences may be explained by barrier function, mast cell physiology, and itch receptor polymorphisms.