logo Pruritus

Itchy skin disease

Pruritus

Objectives

  • Be familiar with the pathophysiology of pruritus (itch).
  • Be able to list common itchy skin conditions and systemic causes of itch.
  • Be familiar with symptomatic treatment for itch.

Key points

  • Itch is the sensation that results in scratching.
  • Itch is transmitted via C-fibres from free nerve endings in the skin.
  • Lateral spinothalamic tract lesions disrupt itch.
  • Itch can be induced by histamine, substance P, serotonin and opioids.
  • Itch is most often due to skin disease such as dermatitis, urticaria, infestation.
  • Neuropathic itch is often dermatomal.
  • Systemic disease (haematological, liver, kidney, thyroid, malignancy) may cause itch.
  • Treat the cause and relieve symptoms with moisturisers, cooling and sedation.
  • Note the spelling of pruritus.

Introduction

The predominant cutaneous symptom is itch (pruritus). Itch can be localised or generalised, intermittent or continuous. It can occur in the absence of skin disease but is more frequently caused by a dermatological problem. Little is known about the mediators or the neurological processes involved in either the detection of an itch stimulus or the induction of the main response to itch, scratch. Symptom control remains unsatisfactory.

Pathophysiology of itch

Itch is a subjective and variable sensation resulting in scratching. Although itch is mostly unpleasant, scratching is a pleasure, perhaps because the pain of scratching reduces the itch.

Peripheral nervous system

There are complex chemomediators on free nerve endings transmitted by C–fibres. It is possible that itch is low intensity pain at dermoepidermal junction, but specific itch fibres and nerve endings are now considered more likely. Mechanical and electrical stimuli and chemicals including histamine and substance P may induce itch.

Central nervous system

Itch activates a cerebral network resulting in a strong motor effect – itch provokes scratch, whereas pain results in withdrawal from the painful stimulus. Lesions of the lateral spinothalamic tract disrupt itch, pain and temperature sensations. Itch can be induced by centrally acting serotonin and opioids.

Evaluation of the itchy patient

History should determine what areas are affected by itch and its severity, exacerbating and relieving factors and the time course of the symptoms and signs.

Examine the patient’s skin all over and note the distribution of the itch/rash. Identify primary and secondary skin lesions. Scratching results in picked or linear excoriations, bruises and broken-off hair. Nails used for rubbing appear highly polished.

Perform a full medical examination, particularly if there appears to be generalised itch without a primary skin rash.

Excoriations but no primary lesions

Excoriated dermatitis

Rubbing the skin resulting in bruising

Excoriated insect bites

Excoriated atopic dermatitis

Excoriated nodular prurigo


Localised itch with no primary rash may be due to nerve root impingement resulting in dermatomal neuropathic pruritus. Scratching or rubbing the affected areas may result in secondary hyper/hypopigmentation and lichen simplex (localised lichenified eczema).

Treatment of neuropathic itch may include non-steroidal anti-inflammatory drugs, tricyclic antidepressants and physiotherapy.

Notalgia paraesthetica; hyperpigmentation of the upper back due to rubbing

Postherpetic neuralgia resulting in localised scalp itch


Genital regions are particularly prone to chronic itching.

Pruritus vulvae due to lichen sclerosus

Pruritus ani due to irritant factors


Generalised itchy rashes

A few primary skin disorders are intensely itchy even when there isn’t much rash to see.

Dry skin can be itchy

Itching from scabies is very intense

Itchy buttocks due to dermatitis herpetiformis

Urticaria tends to result in rubbing rather than scratching


Generalised itch without primary skin disease

Itch may due to various systemic diseases, but in most cases the mechanism is not understood and symptoms may be very severe. Increased opioidergic tone may have a role.

Intense generalised pruritus of central neurogenic origin

Severe pruritus due to chronic renal failure


Treatment of pruritus

Clearly it is important to identify the cause and treat the primary skin condition and dermatitis, which may be secondary to scratching and rubbing. General measures include:

Specific topical antipruritic agents include:

Oral agents