Chronic Pruritus in the Absence of Specific Skin Disease: An Update on Pathophysiology, Diagnosis, and Therapy

Nicoletta Cassano; Gianpaolo Tessari; Gino A. Vena; Giampiero Girolomoni

Disclosures

Am J Clin Dermatol. 2010;11(6):399-411. 

In This Article

Classification of Itch

Two recently proposed classifications of pruritus are based on the neurophysiologic origin of pruritus or the clinical picture and symptoms of the patient. Twycross et al.[16] classified itch into four categories: (i) pruritoceptive (originating in the skin); (ii) neuropathic (lesioned neurons themselves generate itch); (iii) neurogenic (central mediators generate itch without neuronal damage); and (iv) psychogenic (somatoform). Psychogenic pruritus should be suspected only after cautious exclusion of other causes. It is advisable that an expert in psychosomatics or psychiatry should confirm the diagnosis of somatoform pruritus independent of any other organic origin.[17] Psychological factors may influence itch perception or can complicate chronic itch even in the absence of a true psychiatric morbidity.

The International Forum for the Study of Itch (IFSI) distinguished three clinical groups of patients: (i) pruritus on primarily inflamed skin; (ii) pruritus on normal skin; and (iii) pruritus with chronic nonspecific secondary scratch lesions.[1] These three groups can be further classified into six subtypes after clinical and laboratory assessment (table II). Pruritus without skin changes has been previously named 'essential pruritus' or 'pruritus sine materia.' It has been recommended that these two definitions should no longer be used because they may generate confusion.[1] Indeed, most patients with chronic pruritus unrelated to skin diseases have skin lesions secondary to scratching or simply skin dryness. Therefore, it is very important to distinguish a definite skin disease from nonspecific (scratch- or rubbinginduced) skin changes. Pruritus is the most common symptom of most inflammatory skin disorders (e.g. atopic dermatitis, psoriasis, contact dermatitis, urticaria, drug reactions, pemphigoid, dermatitis herpetiformis), parasitic or infectious diseases (e.g. scabies, mycoses, chickenpox), as well as cutaneous T-cell lymphoma.

Nonspecific skin lesions associated with chronic itch include linear excoriations and crusts, skin marking (i.e. lichenification), and excoriated papules and nodules up to the picture of prurigo nodularis.[18] Prurigo nodularis is dominated by the presence of numerous excoriated papules and nodules, leaving hyperpigmented macules on the extensor surface of the limbs and the back.[18] In many cases it is an idiopathic disorder, but in some cases, prurigo nodularis may be the expression of atopic dermatitis or persistent insect bite reactions, and can also be diagnosed in patients with systemic infections such as hepatitis C virus (HCV), HIV, atypical mycobacteria infections, lymphoproliferative diseases (lymphoma), solid tumors (bladder and gastric cancer), and other diseases.[18] Patients with prurigo nodularis have a high frequency of psychiatric morbidity.[19]

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