Evaluation of pruritus

Diseases

Summary

Pruritus is defined as an unpleasant sensation that causes a desire to scratch. The terms pruritus and itch are used synonymously. Pruritus is the most common subjective symptom in dermatology and may occur with or without visible skin lesions. It may be localized or generalized.

It is important to distinguish between acute and chronic pruritus. Pruritus lasting >6 weeks is defined as chronic pruritus.[1] [2] [3] Based on etiology, chronic pruritus may be classified as being of dermatologic, systemic, neurologic, psychogenic/psychosomatic, mixed, or unknown etiology. Chronic pruritus can be very distressing and refractory to treatment. Its intensity frequently correlates with degree of quality of life impairment, level of stigmatization, severity of depression, and emotional stress.

According to the currently accepted clinical classification, patients with pruritus may be characterized as those with itching on primarily diseased, inflamed skin; pruritus on primarily normal, noninflamed skin; and itchy skin with chronic secondary scratch lesions.[1]

Epidemiology

Itching is a common ailment. European population-based studies report pruritus prevalence (acute and/or chronic [>6 weeks duration]) of between 7% and 17%.[4] [5] [6]

Prevalence increases with age. One systematic review and meta-analysis reported an overall pooled prevalence of pruritus of 21% in older people (ages ≥60 years).[7] One large epidemiologic study conducted in Germany found an increase from 12.3% among young adults (16-30 years) to 20.3% among those aged 61-70 years.[5]

In a self-reported morbidity study conducted in Norway, itch was the most frequently mentioned skin symptom (7%).[4] [6] Patients reporting itch were younger, predominantly female, and more distressed; they had lower income, poorer social support, and experienced more negative life events.[8] Itch was reported significantly more often by men from East Asia (18%) and the Middle East/North Africa (13%).[6]

Pruritus is a common symptom of many skin diseases.[2] [9] For example, it is a cardinal symptom of atopic eczema, and all patients with this disease are believed to have pruritus at some point during their illness.[10] Similarly, about 70% to 90% of patients with psoriasis have pruritus.[11] [12] [13] [14] Pruritus may also complicate other systemic diseases, such as chronic renal failure, blood malignancies, or liver disorders.[15] For instance, the frequency of chronic pruritus in hemodialysis patients has been estimated to be between 25% and 55%.[16] [17] [18]

Pathophysiology

Pathophysiology depends on the underlying disease. Itch may be induced or modulated by many different mediators, including histamine, acetylcholine, catecholamines, hemokinins, chemokines, cytokines (interleukin 2, interleukin 31), neuropeptides, endothelin, endovanilloids, endocannabinoids, hormones of the hypothalamus-pituitary axis, kallikreins, proteases, prostaglandins, leukotriene B4, neurotropic peptides, and opioids.[19]

A specific neuronal pathway for itch has been identified. Pruritic stimuli are transmitted mainly by mechano-insensitive unmyelinated afferent C-fibers that have a particularly low conduction velocity, large innervation territories, and high transcutaneous electrical threshold.

In the spinal cord, the pruritic stimuli are transferred by specific pruriceptive neurons of dorsal horns to the posterior part of the ventromedial thalamic nucleus, which projects to the dorsal insular cortex. Itch pathway neurons have been identified in the spinal cord showing expression of gastrin-releasing peptide receptors.[20] [21] [22]Induced itch stimuli coactivate the anterior cingulate cortex, supplementary motor area, and inferior parietal lobe predominantly in the left hemisphere.

Following itch induction, the multiple activated sites in the brain argue against the existence of a single itch center and reflect the multidimensionality of pruritus.[23] Importantly, it has been demonstrated that the brain activity in patients suffering from chronic itch upon pruritic stimuli differs significantly from that observed in healthy subjects.[24]

Library

Acute urticaria: typical wheals
Urticaria: wheals
Scabies
Scabies: typical lesions within interphalangeal areas
Plaque type psoriasis
Psoriasis: symmetric plaques on the back covered with thick scales
Solar urticaria: photoprovocation upon UVA exposure
Atopic dermatitis: erythema, excoriations, and lichenification in popliteal area
Lichenification due to chronic rubbing in a patient with atopic dermatitis
Prurigo nodularis: a disease with extensive scratch lesions
Prurigo nodularis: note sparing of upper part of back, which is difficult to access for scratching
Prurigo nodularis: secondary scratch lesions
Atopic dermatitis: white dermographism
Lichen planus: lacy network traversing the buccal mucosa
Lichen planus: flat, violaceous papules with visible Köbner phenomenon (arrow)
Dermatitis herpetiformis: typical lesions on extensor surface of forearm
Dermatitis herpetiformis: highly pruritic vesicles, small blisters, and erosions on extensor surfaces of extremities
Bullous pemphigoid: tense blisters and erosions on erythematous background

Citations

Key Articles

Ständer S, Weisshaar E, Mettang T, et al. Clinical classification of itch: a position paper of the International Forum for the Study of Itch. Acta Derm Venereol. 2007;87:291-294.[Abstract]
Millington GWM, Collins A, Lovell CR, et al. British Association of Dermatologists' guidelines for the investigation and management of generalized pruritus in adults without an underlying dermatosis, 2018. Br J Dermatol. 2018 Jan;178(1):34-60.[Abstract][Full Text]
Weisshaar E, Szepietowski JC, Dalgard FJ, et al. European S2k guideline on chronic pruritus. Acta Derm Venereol. 2019 Apr 1;99(5):469-506.[Abstract]
Ständer S, Pereira MP, Berger, T; et al. IFSI-guideline on chronic prurigo including prurigo nodularis. Itch. 2020;5:e42.
Eichenfield LF, Tom WL, Chamlin SL, et al; American Academy of Dermatology. Guidelines of care for the management of atopic dermatitis. Part 1: Diagnosis and assessment of atopic dermatitis. J Am Acad Dermatol. 2014;70:338-351.[Abstract][Full Text]

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