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Chapter 18: Pruritic Skin Conditions

TEY Hong Liang; LOW Meiyin Lynette Charlene

INTRODUCTION

Pruritus (itch) can be defined as an unpleasant sensory and emotional experience that provokes a desire to scratch. In the approach to the management of a pruritic skin condition, identification of an underlying cause is important. The first step is to determine the presence of an underlying dermatological disease. If no primary dermatosis is identified and only secondary excoriations from chronic scratching are present, the patient should be evaluated for an underlying systemic and/or neurological cause for the pruritis. Psychogenic causes are considered only after the exclusion of organic causes.

ETIOLOGIES OF CHRONIC PRURITUS

There are four major categories of conditions causing chronic pruritus—dermatological, systemic, neurological, and psychogenic (Table 18.1). In some patients, more than one factor contributes to the occurrence and such cases are classified as “mixed.” Dermatological diseases are the most common cause, being present in 60% to 95% of patients consulting the dermatological clinic for chronic itch. Systemic disease accounts for 15% to 40% of patients presenting with generalized pruritus.

Table 18.1Etiological Classification of Chronic Pruritus
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Table 18.1 Etiological Classification of Chronic Pruritus
Category Etiological Subgroups Example of Diseases
Dermatological Inflammatory dermatoses Eczema (endogenous and exogenous), psoriasis, contact dermatitis, dry skin, elderly pruritus, drug reactions, lichen planus, lichen sclerosis, pityriasis rosea, scars
  Infectious dermatoses Mycotic, viral infections, bacterial folliculitis, scabies, pediculosis, arthropod reactions, insect bites, parasitosis
  Autoimmune dermatoses Bullous dermatoses (especially dermatitis herpetiformis and bullous pemphigoid), dermatomyositis, scleroderma
  Genodermatoses Darier's disease, Hailey-Hailey disease, congenital ichthyoses, epidermolysis bullosa pruriginosa
  Dermatoses of pregnancy Polymorphic eruption of pregnancy, pemphigoid gestationis, prurigo gestationis
  Neoplasms Cutaneous T-cell lymphoma (especially erythrodermic variants), cutaneous B-cell lymphoma, leukemia cutis
Systemic Endocrine and metabolic diseases Chronic renal failure, liver diseases with or without cholestasis, hyperthyroidism, diabetes mellitus, carcinoid syndrome, malabsorption
  Infectious diseases HIV infection, parasitosis
  Hematological diseases Polycythemia rubra vera, Hodgkin's disease, non-Hodgkin's lymphoma, leukemia, systemic mastocytosis
  Visceral neoplasms Solid tumours of the cervix, prostate, or colon
  Pregnancy Pruritus gravidarum with and without cholestasis
  Drug-induced pruritus Opioids, ACE inhibitors, aspirin, epidermal growth factor receptor (EGFR) inhibitors
Neurological Peripheral nervous system Post-herpetic neuralgia, brachioradial pruritus, notalgia paresthetica
  Central nervous system Stroke, neoplasm, abscess, multiple sclerosis, Creutzfeldt-Jakob disease
Psychogenic Neuroses Somatoform pruritus/functional itch disorder, obsessive-compulsive disorders, factitious dermatitis, impulse control disorder (neurotic excoriation and a subgroup of prurigo nodularis)
  Psychoses Delusion of parasitosis, schizophrenia with tactile hallucination
Mixed Co-existence of systemic, dermatological, neurological, and/or psychogenic itch Uremia, HIV-associated pruritus

CLINICAL EVALUATION

In a patient presenting with chronic pruritus, the history is directed at elucidating the cause and to provide insight into the disease process. In the physical examination, an attempt is made to identify the presence of primary skin pathology or features of an underlying systemic disease that may account for the itch. It is essential ...

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