Itching (comezon)

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Dermatology anD general health

Sue handfield-Jones

making a diagnosis in patients with itch is to determine whether there is an underlying inflammatory skin disease causing the itch or whether the itch is in the context of normal skin. Whilst this appears straightforward, in practice it can be difficult as the effects of scratching can make assessment of the skin difficult, andrashes can be evanescent.6,7 The main points to consider in the history and examination of itch are listed in Tables 1 and 2. Many skin conditions cause pruritus, either localized or generalized, and these are covered in the relevant sections in these issues. Dermatoses that are characterized by severe itch Whilst many inflammatory dermatoses cause itch, some, for reasons unknown, cause more severeitch than others. These are: • eczema of all types, including prurigo nodularis and lichen simplex • scabies • lichen planus • urticaria • immunobullous disorders, including dermatitis herpetiformis • Grover’s syndrome: this uncommon acantholytic dermatosis usually affects older men and is often associated with sun exposure. The rash is very non-specific clinically but can be diagnosed on skinbiopsy. Easily missed rashes Key to the management of patients with pruritus is distinguishing those who have rashes from those who do not. Some rashes are easily missed, either because they cannot be distinguished from scratch damage or because they are transient and may not be visible when the patient is in clinic. Dry skin – this is one of the most common causes of itch but the clinical signs canbe subtle or overlooked. Other terms used include xerosis, winter itch, senile pruritus and asteatotic eczema. The changes are most common on the lower legs. Exacerbating factors include age, low atmospheric humidity (centrally heated houses in winter) and overuse of soap and detergents on the skin, especially with hot water. Patients with hypothyroidism

Itching, also known aspruritus, is the major symptom of skin disease and is unique to skin and (less commonly) mucosae. It is a cause of great distress to patients. the pathophysiology of itch is complex, with a range of inflammatory mediators being implicated. Itch is not a diagnosis and itchy patients always need careful evaluation. Itch can be associated with a rash or can occur on normal skin. Some rashes such as lichenplanus are characterized by severe pruritus. It is important to detect signs of subtle inflammatory skin disease because a patient presenting with generalized itch in the absence of any rash needs to be investigated for underlying systemic causes. Systemic disease associated with itch includes malignancy, both haematological and solid tumours, renal, hepatic and thyroid dysfunction and infections.treatment of itch is difficult, with a range of topical, physical and systemic treatments used.

Keywords dermatoses; itch; pruritus; rash

Definition and general information
Itch is the unpleasant sensation that leads to the desire to scratch the skin. The terms ‘itch’ and ‘pruritus’ can be used interchangeably. Itch can be so severe that it causes insomnia, and scratching can be so intensethat the skin is left raw and bleeding. Chronic itch has a major impact on quality of life.1 Reproducible measurement of itch for research is difficult. Visual analogue scales can be used to give an indication of itch severity. Scratching can be measured using movement detectors.2 The pathophysiology of itch is still under investigation. Itch is caused by a complex interplay between chemicalmediators derived from both skin and blood with peripheral and central neural mechanisms. Whilst histamine is the best known mediator of itch there are many others. The sensation of itch is transmitted via unmyelinated pain fibres and functional imaging of the brain shows that multiple areas are involved in itching and scratching.3–5

History: key points
• time-course of itch: duration, onset,...
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