Pruritus

Introduction

Pruritus is commonly known as itching. It is an uncomfortable, irritating sensation that creates an urge to scratch that can involve any part of the body.
It is the most common unpleasant experience involving the skin; provokes a desire to scratch.
It may be elicited by many normally occurring stimuli e.g.

  • Light touch
  • Temperature change
  • Emotional stress
  • Chemical, mechanical, thermal and
    electrical stimuli

It is mediated by the release of chemical
substances e.g. histamine, kinins, and proteases.
Prostaglandin E lowers the threshold for
histamine-induced pruritus, while
enkephalins, pentapeptides which bind
to opiate receptors in the brain modulate
pain and itching centrally

Symptoms and clinical features of pruritus

At a low level, it may merely be annoying.
It may actually torture the patient, interferes with sleep and lead to less than optimal performance.
There are great variations from person to person.
In the same person there may be variation in reactions to the same stimuli.
In the elderly, senile pruritus due to dry skin may be particularly bothersome.
Psychologic trauma, stress, absence of
distractions, anxiety, and fear may all
enhance itching.
It tends to be most severe at the time of
undressing for bed.
There are also regional variations.
The ear canals, eyelids, nostrils, and
perianal and genital areas are especially
susceptble to pruritus.
It may be localized or generalized
It may or may not be associated with skin lesions.
Excoriations are typically linear and occur where the patient can reach with his hands.
The middle of the back is typically spared except when the patient has used a back scratcher.
The scratch is usually erythematous,
with many tiny erosions scattered along it.
Fresh marks are usually weepy or bloody; older ones crusted.
Lesions may become impetiginized.
In addition to excoriations, some patients
may have smooth, shiny fingernails (the
polished nails of chronic pruritus)
Pruritus without skin lesions suggests:

  1. Biliary obstruction
  2. Diabetes mellitus
  3. Uraemia
  4. Lymphoma
  5. Hyperthyroidism
  6. Adverse reaction to medicines e.g.
    Histamine liberators, opioids
  7. Occult scabies
  8. Pediculosis
  9. Onchodermatitis
  10. Dermatitis herpetiformis
  11. Atopic eczema in remission
  12. HIV/AIDS
  13. Systemic mastocytosis

Polycythaemia vera is a notable cause of
pruritus; usually induced by temperature
changes.
Some patients complain of pruritus provoked by bath or immediately post-bath.
Factors include:

  1. Aquagenic pruritus
  2. Temperature-dependent pruritus due to cold/heat
  3. Cholinergic pruritus (when the core temperature is increased and there is sweating)
  4. Allergy to bath sponge or soap
  5. Mechanical scrubbing of the skin with coarse sponge causing degranulation of mast cells
  6. A forceful jet of water from the shower may trigger pruritus in some cases.

Differential diagnoses

  • All the above causes of pruritus

Complications of pruritus

  1. Sleep disturbance
  2. Less than optimal performance at home, work or school
  3. Emotional disturbance
  4. Suicidal ideation

Investigations

  • As suggested by meticulous history and physical examination

Treatment for pruritus

Treatment objectives

  1. Suppress itch
  2. Identify and treat cause(s)
  3. Improve quality of life
  4. Prevent complications

Drug treatment

A. General

Ketotifen

  • Adult: 2 mg orally taken before bath (with food)
  • Child 3 years and over: 1 mg orally twice daily

B. Depressed, itchy individuals

Doxepin

  • Adult initially 75 mg orally daily in divided doses or as a single dose at bedtime
  • Increased if necessary to a maximum of 300 mg daily in 3 divided doses
  • Up to 100 mg may be given as a single dose
  • Elderly: initially 10-50 mg daily; range of 30 –
    50 mg daily may be adequate
  • Not recommended for children
    Pruritus associated with partial biliary obstruction and primary biliary cirrhosis

Colestyramine

  • Adult: 4-8 g orally daily in water (or other suitable liquid)
  • Child
    • 1 month – 1 year: 1 g orally once daily mixed with water;
    • 1-6 years: 2 g once daily;
    • 6-12 years: 4 g once daily;
    • 12 – 18 years: 4 – 8 g daily, adjusted according to response in all age groups

C. Pruritus of renal failure

Activated charcoal

  • Adult: 50 g orally initially then 50 g every hours.
  • Treat vomiting with an anti-emetic
    because it may reduce the efficacy of charcoal treatment
  • In cases of intolerance reduce the dose and increase frequency of administration (e.g. 25 g every 2 hours or12.5 g every hour).
  • This may however compromise efficacy

Or:

Ultra Violet B therapy

D. Localized pruritus

  • Corticosteroid creams for inflammatory skin disease

Or:

Crotamiton cream 10%

  • Adult: apply topically 2-3 times daily
  • Child:
    • apply once daily for child below 3 years;
    • over 3 years: apply 2-3 times daily

Or:

Urea 10% hydrocortisone cream 1 %,
Adult and child: dilute with aqueous cream in first 1 week of use if stinging occurs

Or:

Emulsifying ointment BP

  • Adult and child: can be used as soap
    substitute; rub on skin before rinsing off completely

Or:

Doxepin hydrochloride

  • Adult: apply thinly 3-4 times daily (coverage should be less than 10% body surface area)

Adverse drug reactions, caution and contraindications

Colestyramine:

  • Counsel patients
  • Other drugs should be taken at least 1 hour before, or 4 -6 hours after colestyramine to reduce possible interference with absorption
  • May cause constipation and gastrointestinal discomfort
  • Interferes with the absorption of fat-soluble

vitamins

  • Supplements of vitamins A, D and K may be required

Activated charcoal:

  • Risk of aspiration in drowsy or comatose patients
  • Risk of intestinal obstruction in patients with reduced gastro-intestinal motility
  • Black stools

Doxepin:

  • Caution in patients with glaucoma, urinary retention, and severe liver impairment
  • May cause drowsiness, local burning, stinging, irritation and dry mouth

Prevention of pruritus

  • Use a cleansing bar (instead of soap) for baths
  • Pat rather than rub skin dry after bath and immediately lubricate skin with petroleum jelly or emulsifying ointment