• Clinical science

Pruritus

Abstract

Pruritus is the medical term for itching of the skin. Pruritus may be generalized or localized, acute or chronic. Localized pruritus is usually caused by dermatological conditions (e.g., allergic contact dermatitis), whereas generalized pruritus can also have systemic (e.g., uremia, hyperbilirubinemia), neurologic, psychogenic, or mixed causes. The evaluation of pruritus is based on a complete medical history and a detailed skin examination. Treatment of pruritus involves symptomatic relief and management of the underlying disease.

Pathophysiology

  • Poorly understood
  • Trigger → activation of afferent C-fibers in the skin → interpreted by the CNS as pruritus
    • Triggers include mechanical, chemical, or thermal stimuli, or exposure to certain mediators (e.g., histamine, serotonin, prostaglandins, kinins, etc.)
  • Scratching and rubbing the skin → stimulates inhibitory circuits and pain receptors → decreases pruritus in the short-term (however, in many scenarios, scratching increases irritation and ultimately worsens itching)
    • Gate control theory: Painful input transmitted by A-fibers inhibits the transmission of pruritic input from the C-fibers.

Diagnostics

Medical history

  • Initiating factors
  • Location: generalized vs. localized
  • Onset: acute vs. chronic (> 6 weeks); time of day ; season
  • Allergies
  • Travel and environmental history
  • Underlying disorders and medications
  • Psychiatric history
  • Substance use

Physical examination

  • Skin examination
    • Goal: Determine whether there are primary skin lesions, secondary skin lesions , or no skin lesions at all.
    • If skin lesions are visible, it is necessary to identify:
      • Location
      • Type of lesion
      • Secondary changes as a result of scratching
    • Visible skin lesions are not always present!
  • General physical examination
    • Goal: Determine if there is evidence of an underlying disease.

A complete physical examination should always be performed!

Further diagnostics

Further evaluation depends on presentation and examination findings.

  • Generalized pruritus
    • Primary skin lesions present (likely skin disease) → consider skin biopsy (if indicated) or empirical treatment
    • Primary skin lesions absent (likely systemic disease) → CBC with differential, liver function tests, renal function tests, TSH, chest radiograph
  • Localized pruritus
    • Primary skin lesions present (likely dermatologic condition) → further evaluation depends on specific site affected
    • Primary skin lesions absent (likely neuropathic or psychogenic pruritus) → psychiatric/neurological evaluation

Pruritus without primary skin lesions must always be investigated, as it may be a sign of a serious underlying condition like a malignancy!

Differential diagnoses

The differential diagnoses listed here are not exhaustive.

Treatment