Itchy skin disease
- 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.
- 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.
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
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 (itchy vulva)
- Pruritus ani (itchy anus)
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.
- Winter itch affects the elderly and is thought related to xerosis (dry skin).
- Scabies: look for burrows and nodules between fingers, wrists and elbows. Signs may be subtle. Immune response results in the rash and generalised itch; mediators are toxic to mites and evoke scratch. Treat with insecticides.
- Dermatitis herpetiformis is an immunobullous disease affecting extensor surfaces due to gliadin hypersensitivity and associated with gluten enteropathy.
- Urticaria - shifting itchy wheals that may be absent at the time of examination or may not occur at all.
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.
- Biliary or obstructive liver disease especially primary biliary cirrhosis
- Chronic renal failure especially dialysis patients
- Haematological disease especially iron deficiency, polycythaemia rubra vera, lymphoma and myeloma
- Advanced malignancy
- Thyroid disease (hypo- or hyper-)
- Human immunodeficiency virus infection
- Neurological disease including some strokes, multiple sclerosis and brain tumours
- So-called ‘neurotic excoriations’ of psychogenic or central nervous system origin
- Drugs: opioids, aspirin, acetylcholinesterase (ACE) inhibitors and others
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:
- Advise short nails to minimise damage
- Wear cool, loose and smooth clothing
- Apply emollients to treat dryness and relieve itch
- Cool affected areas using water and creams containing menthol and/or camphor
- Cool or conversely burning-hot showers frequently provide relief
- Relaxation: music therapy, self-hypnosis and exercise programmes may help
- Phototherapy with UVB and/or UVA
Specific topical antipruritic agents include:
- Topical steroids; use mild products to avoid skin atrophy
- Topical anaesthetics/antihistamines; these may sensitise, i.e. provoke contact allergic dermatitis
- Conventional antihistamines may act centrally as they are sedative
- Antidepressants such as amitriptyline have anthistamine and neural effects
- Slow release serotonin reuptake inhibitors and in some instances antipsychotics may help
- Opiate antagonists esp. naltrexone
- Thalidomide probably is effective because of its potent anti-tumour necrosis factor (TNF) action.