Pruritus

Question 1

Non-dermatological disease Mechanism

Answer 1

• Systemic: Hepatogenic and nephrogenic pruritus
• Neurogenic/neuropathic
• Psychogenic

Question 2

Nondermatological Etiologies of Chronic Pruritus

Answer 2

• Adverse drug reaction
  
  • Psychiatric/mood disorders
  • Chronic renal failure
  • Cholestasis
  • Hepatitis
  • Thyroid disease (hyper or hypothyroid)
  • Iron deficiency
  • HIV infection
  • Parasitic infection
  • Malignancy
  • Peripheral neuropathies
  • Diabetes mellitus
  • Multiple sclerosis
  • Hemochromatosis

Question 3

Novel pruritogenic receptors

Answer 3

1. Vanilloid receptor TRPV1
2. Ccannabinoid receptors
3. Protease-activated receptor (PAR-2)
4. Opioid receptors

Question 4

Histamine-induced Pathophysiology (It’s not pain)

Answer 4

1. pruritogenic nerver ending receptor: Unmyelinated C-fiber
2. Mediator: Histamine
3. Dorsal horn
4. SPINOTHALAMIC tract: superficial portion of the dorsal horn lamina 1
5. CROSS MIDLINE
6. Lateral thalamus
7. anterior cingulate gyrus and sensorimotor cortex

Question 5

Opioid induced itch

Answer 5

• central itch
  - μ-receptor produces itch
  - κ-receptor agonism inhibits itch
• Treatment
  - Rotate/ Reduce dose opioid
  - Mirtazapine
  - Naltrexone
  - Subhypnotic dose Propofol

Question 6

Other mediators

Answer 6

serotonin, substance P, cytokines, proteases, prostaglandin E, opioid peptides, acetylcholine, bradykinin, and dopamine

Question 7

Non-pharmacological treatments

Answer 7

• Maintain a cool, humidified environment.
  
  • Eliminate irritating or tight clothing.
  • Avoid topical products with fragrances, alcohol, wool, alkaline soap, and potential allergens.
  • Limit bathing to once per day with a non-soap, low pH cleanser (e.g., Cera-Ve, Cetaphil, Aveeno, Dove) and lukewarm water temperature.
  • Wash gently; cleanser film should be rinsed off completely and skin should be patted lightly to dry.
  • Within 3 minutes after bathing, an emollient cream or ointment should be applied liberally to the skin.
  • Emollients (e.g., Aquaphor, Eucerin, Cera-Ve) should be applied twice daily in addition to after bathing.
  • Emollients should be refrigerated and can be compounded with 1% menthol, 10% urea, or 10% LCD to increase their effectiveness.

Topical use of doxepin 5% cream three to four times per day, capsaicin 0.075% cream three to five times per day, or pramoxine 1% cream four times per day.

uremic and hepatogenic pruritus

Question 8

Systemic Medications for Pruritus

Answer 8

Antihistamine: Histamine-induced pruritus, nocturnal pruritus, intractable pruritus

• Hydroxyzine 25-100 mg q8h
• Doxepin10-50 mg qhs: renal itch
• TCA

Steroid

Neuroleptic: Psychogenic itch,malignancy, uremic and hepatogenic pruritus

• Paroxetine 20-50 mg qd
• Mirtazapine15-30 mg qhs

Opiod antagonist: Hepatogenic pruritus, uremic

• Naltrexone 25-75 mg qd
• Butorphanol 1-4 mg intranasally qd

Antiseizure: Neurogenic pruritus, HD, intractable pruritus

• Gabapentin 900-1800 mg qd
• Gabapentin 100mg PO post HD three times a week

Antiemitic: Intractable pruritus, uremic and hepatogenic pruritus

• Ondansetron 8 mg q4h (IV or PO)

Anti TNF: Pruritus of HIV, uremic pruritus, prurigo nodularis

• Thalidomide 50-100 mg qd

Miss.

• Charcoal 6 g qd Uremic pruritus
• Cholestyramine 4-16 g qd Hepatogenic pruritus, uremic pruritus
• Rifampin 300-600 mg qd Hepatogenic pruritus
• Propofol 10-15 mg IV bolus, then 1 mg/kg/hr IV Hepatogenic pruritus, intractable pruritus

Question 9

Drugs of Choice

Answer 9

• Nephrogenic pruritus: Broadband ultraviolet B phototherapy → Mirtazapine
  
  • Hepatogenic pruritus: Mirtazapine → Butorphanol
  • Psychogenic pruritus: Mirtazapine → Paroxetine
  • Dermatological pruritus: Hydroxyzine → Doxepin
  • Nocturnal pruritus: Hydroxyzine → Mirtazapine

Question 10

Cholestatic pruritus

Answer 10

• Generalized, involved palms and soles.
• Bile acid accumulate in the liver and intestines, as pruritus can be palliated with rifampin, a potent liver and intestinal enzyme inducer, or by resin binders.
• Endogenous opioids (mu-receptor agonists in particular), which effect the brain. The serotonin system may mitgate this effect, as evidenced by a decrease in pruritis with the use of selective serotonin reuptake inhibitors (SSRIs).

Question 11

Cholestatic Pruritis approach

Answer 11

1. biliary drainage: stent/ drain placement
2. bile resin binders
3. Hepatic enzyme inducer: rifampin
4. Mu-antagonist; naltrexone or naloxone or Butorphanol
5. SSRI; sertraline, paroxetine.