Background

  • Chronic pruritus defined as itching >6 months
  • May be generalized or localized to a specific body part
  • 14-24% may have an underlying systemic disease



Differential Diagnosis and Evaluation (Yosipovitch)

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Note:
  • Pruritus of Undetermined Origin (PUO) is defined as pruritus >3 weeks of undetermined origin (ultimately remains idiopathic in 70-80% with PUO)
    • Periodic re-evaluation is warranted if no cause is identified
  • The presence of a rash does not necessarily indicate a primary skin disease; lichenification, prurigo nodules, patches of dermatitis, and excoriations can result from rubbing and scratching
  • "Wheal-less urticaria" is thought to occur when histamine and other released mediators are sufficient to trigger a sensory response but not vascular effects (reported in case of aquagenic pruritus, contact urticaria, dermatographic urticaria, cholinergic urticaria)
  • Polycythemia vera - ~50% have severe, prickly, distressing discomfort within minutes of water contact ("bath itch") which lasts 15-60 min, may precede overt disease onset by several years, and may be associated with elevated serum/urinary histamine levels but antihistamines are generally ineffective
  • Hodgkin's disease - 30% have pruritus whch may be an early or presenting symptom, worse on lower body, burning and more intense at night, and the itch may correlate with disease severity
  • Brachioradial pruritus - sunlight-induced chronic episodic pruritus localized to outer aspect of elbow and adjacent lower and upper arms, more common in fair-skinned people in tropical climates; treatments include sun protection, topical camphor or menthol, cervical spine manipulation, capsaicin, topical anesthetics



Treatment (Yosipovitch)

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  • Example approach for chronic idiopathic pruritus:
    • Start with frequent moisturization, mild cleansers, topical antipruritic agents (e.g. pramoxine), avoidance of trigger factors (e.g. heat due to excessive bedding)
    • First line systemic therapy is often sedating antihistamines, but efficacy is limited
    • Second line systemic therapy may be gabapentin, starting at 300 mg/day and progressing up to 2400 mg/day in divided doses, with mirtazapine (7.5-15 mg) added at night if still symptomatic)



References