Pruritic Condition

Nerve fiber involvement
1. Origin of itch is within skin Free Nerve Endings
  1. Fibers most concentrated in wrists and ankles
  2. Unmyelinated C fibers to dorsal horn in spinal cord
2. Scratching is a spinal reflex response
3. Ascends to cerebral cortex via Spinothalamic Tract
Chemical mediators
1. Substance P
2. Opioid and nonopioid peptides
3. Somatostatin
4. Neurokinin A
5. Histamine
6. Serotonin
7. Prostaglandins
External mediators
1. Skin inflammation
2. Environmental heat or dryness
3. Vasodilation
4. Psychological concerns

Group 1: Pruritis on Diseased Skin
1. Dermatologic causes
Group 2: Pruritus on Non-Diseased Skin
1. Systemic, neurogenic or psychogenic causes
Group 3: Chronic reactive lesions from skin manipulation (rubbing, picking, scratching)
1. Mixed presentations and complications from primary condition

Identify primary Dermatologic Causes of Pruritus
1. Atopic Dermatitis: Atopy, Asthma, or Urticaria
2. Contagious contacts (Pediculosis or Scabies)
3. Pathognomonic skin lesions (e.g. Psoriasis, Eczematous Dermatitis, Dermatophytosis)
4. Consider Localized Causes of Pruritus
5. Consider Timing (Xerotic Eczema worse in winter)
Identify potential exposures
1. See Medication Causes of Pruritus
2. Travel history and new animal exposures (fleas, Scabies, Dermatophytosis)
3. Contagious Contacts (e.g. Parvovirus B19, Varicella)
4. Consider Environmental Causes of Pruritus (e.g. solvents, cleaners, adhesives)
  1. See Allergic Contact Dermatitis
  2. See Occupational Contact Dermatitis
  3. See Irritant Contact Dermatitis
  4. Ask about new skin or hair products (e.g. soaps, lotions, detergents, cosmetics)
  5. Consider Photodermatitis
Review mental health concerns (e.g. Major Depression)
Consider Systemic Causes of Pruritus
1. Observe for cholestasis (e.g. Jaundice, Hepatomegaly)
2. Consider Renal Failure Associated Pruritus (e.g. Nausea, decreased Urine Output, Fatigue)
3. Consider Thyroid disease (esp. Hyperthyroidism)
4. Consider malignancy (e.g. Night Sweats, weight loss, Fatigue, Lymphadenopathy)

Approach
1. Base lab testing on history and physical
2. Avoid broad shotgun approach to lab testing
3. Consider lab testing in >2 weeks of persistent Pruritus without other obvious causes
Dermatologic Cause Evaluation
1. Skin Scrapings for Scabies and Dermatophytosis
2. Skin biopsy
  1. Mastocytosis
  2. Mycosis Fungoides
  3. Autoimmune Bullous Disease
Systemic Cause Evaluation (esp. age >65 years, generalized Pruritus, chronic Pruritus >6 weeks)
1. Thyroid Function Test (evaluate for Hyperthyroidism)
2. Complete Blood Count (CBC)
3. Comprehensive Metabolic Panel
  1. Serum Creatinine
  2. Blood Urea Nitrogen (BUN)
  3. Liver Function Tests (evaluate for cholestasis)
    1. Serum Bilirubin
    2. Alkaline Phosphatase
4. Iron Studies
  1. Serum Ferritin
  2. Serum Iron
  3. Iron binding capacity
5. Other labs to consider