Itching, an unpleasant sensation leading to scratching.

Most common symptom in dermatology that may occur with or without visible skin lesions.

Reported as a symptom by patients with more than 7 million outpatient visits per year in the US, and 25% of such patients are 65 years or older.

May be localized or generalized in nature.

Incidence increases with age.

Affects nearly one third of nursing home patients.

In a Turkish study prevalence of chronic pruritus in a geriatric population in patients aged 65 years was 12% and nearly 20% for patients 85 years or older(Yalcin B et al ).

More common in women than men.

More common in Asians than whites.

May be induced or altered by histamine, catecholamines, chemokines, interleukin 2, interleukin 31, endothelin, neuropathies, acetylcholine, kallikreins, prostaglandins, proteases, leukotriene B4 and opioids.

The process may be acute or chronic, and if it lasts longer than 6 weeks it is referred to as chronic pruritus.

Acute disease is a physiologic symptom while chronic pruritus is a common symptom of a systemic or dermatological disorder.

Associated with a reduction in quality of life, as it may be as debilitating as chronic pain.

Associated with impaired sleep patterns, mood disturbances, anxiety, depression.

All of the above symptoms may exacerbate itching.

Severe itching should prompt an evaluation for evidence of underlying kidney, liver, or thyroid disease, underlying malignancy and dermatitis herpetiformis.

Dry skin is a common cause.

Chronic disease classified as dermatologic, systemic, neurologic, psychogenic, mixed or of unknown etiology.

Commonly associated with dermatological diseases including atopic eczema, psoriasis, lichen planus, and scabies.

May complicate systemic diseases, such as chronic renal failure, blood malignancies or liver disorders.

Pruritus is present at some point in the course of polycythemia Vera in approximately 65% of patients and is generally localized to the trunk and proximal extremities and classically occurs following a hot shower.

Biological processes contributing to itching includes loss of barrier function, immunosenescence and neuropathy.

Seen in 22-70% of hemodialysis patients.

Chronic pruritus associated with impaired quality of life, emotional distress and depression.

Aquagenic type refers to itching after exposure to water and is virtually pathognomonic for polycythemia rubra vera.

May be characterized as those with itching on primarily diseased skin or normal noninflamed skin, and chronic secondary scratch lesions.

The major symptom in atopic eczema, with essentially all patients suffering with this process sometime during the illness.

About 70% to 90% of patients with psoriasis suffer from pruritus.

Itching elicits secondary skin changes due to the scratching, rubbing, and picking.

The presence of secondary skin changes does not rule out a systemic disease.

Secondary skin changes of excoriation and nonspecific dermatitis can impair the diagnosis of cutaneous and non-cutaneous causes of itching.

A neuronal pathway for itch has been identified with stimuli transmitted mainly via small itch selective mechano-insensitive unmyelinated afferent C-fibers that have a particular low conduction velocity, large innervations territories and high transcutaneous electrical threshold.

Pruritic stimuli are transf2242ed via specific neurons of dorsal horns to the posterior part of the ventromedial thalamic nucleus, which projects to the dorsal insular cortex.

A number of mediators are involved in the sensation of itch and histamine triggered neurons and nonhistaminergic neurons may be involved.

Involves synapses of these neurons with secondary neurons cross to the contralateral spinothalamic tract and ascend to multiple sites in the brain that are involved with sensation, emotion, memory, reward and evaluation processes.

Chronic itch patients often have peripheral and central nervous system hypersensitization.

Itch stimuli induced predominantly in the left hemisphere.

Chronic pruritus frequently refractive to treatment.

Chronic pruritus exacerbated by sleep disturbances, and vice versa.

Can lead to frustration and depression.

Age associated changes that contribute to pruritus include a sensory neuropathy most commonly due to diabetes which can cause generalized itch, and neural impingement caused by localized pruritus commonly found in the genital area.

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