Chapter 120: Pruritus

Pruritus (the Latin word for itch) is defined simply as the desire to scratch.

It is one of the most important dermatological symptoms and is usually a symptom of primary skin disease with a visible rash. However, it is a subjective symptom and diagnostic difficulties arise when pruritus is the presenting symptom of a systemic disease with or without a rash—‘pruritus sine materia’. An associated rash may also be a manifestation of the underlying disease.

The broad differential diagnoses of pruritus are:

• skin disease

• systemic disease

• psychological and emotional disorders

Itch arises from the same nerve pathway as pain, but pain and itch are distinct sensations. The difference is in the intensity of the stimulus. Unrelieved chronic itch, like unrelieved pain, can be intolerable and cause suicide. There are many similarities: both are abolished by analgesia and anaesthesia; subdued by counter-irritation, cold, heat and vibration; and referred itch occurs just like referred pain. Antihistamines that act on the H₁ receptor are often ineffective, suggesting that histamine is not the only mediator of itch.¹

Pruritus may be either localised or generalised. Localised itching is generally caused by common skin conditions such as atopic dermatitis (see TABLE 120.1). Scratch marks are generally presented. Pruritus is a feature of dry skin. An intense, localised itch is suggestive of scabies, also known as ‘the itch’.

Itching of the scalp, anal or vulval areas is a common presentation in general practice.

A careful examination is necessary to exclude primary skin disease; a detailed history and examination should be undertaken to determine if one of the various systemic diseases is responsible.

Notalgia paraesthetica is a common localised itch and/or paraesthesia (possibly also pain) in the interscapular area. It is considered to be due to pressure on spinal nerves from spinal dysfunction. It is usually relieved by physical therapy to the thoracic spine (see CHAPTER 24).² Pruritic rashes in children commonly include atopic dermatitis, varicella, urticaria (hives), insect bites and scabies.

Itch without rash (pruritus sine materia) may be a manifestation of systemic disease. It can accompany pregnancy, especially towards the end of the third trimester (beware of cholestasis), and disappear after childbirth. These women are then prone to pruritus if they take the contraceptive pill.^4,5

Systemic causes are summarised in TABLE 120.2 and a summary of the diagnostic strategy model is given in TABLE 120.3.

The history may provide a lead to the diagnosis—the itching of polycythaemia may be triggered by a hot bath which can cause an unusual prickling quality that lasts for about an hour.⁴ On the other hand, the itching may be caused by a primary irritant such as a bubble bath preparation.

Guidelines

• The prevalence of itching in Hodgkin lymphoma is about 30%. The skin often looks normal but the patient will claim that the itch is unbearable.⁴

• Pruritus due to dermographism is the most common of physical urticarias, with an exaggerated wealing tendency in response to stroking of the skin.⁶

• Pruritus can be the presenting symptoms of primary biliary cirrhosis and may precede other symptoms by 1–2 years.³ The itch is usually most marked on the palms and soles.

• Pruritus can occur in both hyperthyroidism and hypothyroidism, especially in hypothyroidism where it is associated with the dry skin.

• Sometimes the cause is not to be found, especially in elderly patients, but is more identifiable in children.

Key history

Enquire about nature and distribution of itching. Consider pregnancy, liver disease and malignancy of the lymphatic system, particularly Hodgkin lymphoma. A careful review of any drug history is important. Note any associated general symptoms such as fever.

Key examination

• General examination of the skin, abdomen and lymphopoietic systems

• Examine for dermographism by firmly drawing a line in the patient’s skin with a tongue depressor and observe for an urticarial response

Key investigations to consider

• Urinalysis

• Pregnancy test

• FBE

• ESR/CRP

• Iron studies

• Kidney function tests

• Liver function tests

• Thyroid function tests

• Random blood sugar

• Stool examination (ova and cysts)

• Chest X-ray

• Skin biopsy

• Allergy patch testing

• Lymph node biopsy (if present)

• Immunological tests for primary biliary cirrhosis (e.g. anti-mitochondrial antibodies)

Treatment

The basic principle of treatment is to determine the cause of the itch and treat it accordingly. Itch of psychogenic origin responds to appropriate therapy, such as amitriptyline for depression.¹

If no cause is found:

• apply cooling measures (e.g. air-conditioning, cool swims)

• avoid rough clothes; wear light clothing

• avoid known irritants

• avoid overheating

• avoid vasodilatation (e.g. alcohol, hot baths/showers—keep showers short and not too hot)

• treat dry skin with appropriate moisturisers (e.g. propylene glycol in aqueous cream)

• topical treatment

  • – emollients to lubricate skin

  • – local soothing lotion such as calamine, including menthol or phenol (avoid topical antihistamines)

  • – pine tar preparations (e.g. Pinetarsol)

  • – crotamiton cream

• consider topical corticosteroids

• sedative antihistamines (not very effective for systemic pruritus)

• non-sedating antihistamines during day

• antidepressants (e.g. doxepin) or tranquillisers (if psychological cause and counselling ineffective)

Scabies

Scabies is a highly infectious skin infestation caused by a tiny mite called Sarcoptes scabiei (see FIG. 120.1). It is common in school-aged children, in closed communities such as nursing homes and in some Indigenous communities. The female mite burrows just beneath the skin in order to lay her eggs. She then dies. The eggs hatch into tiny mites that spread out over the skin and live for only about 30 days. The mite antigen, in its excreta, causes a hypersensitivity rash. Diagnosis is by microscopic examination of skin scrapings. A new IgE diagnostic test is available.

Clinical features

• Intense itching (worse with warmth and at night)

• Erythematous papular rash

• Usually on hands and wrists

• Common on male genitalia (see CHAPTER 117) (see FIG. 120.2)

• Also occurs on elbows, axillae, feet and ankles, nipples of females (see FIG. 120.3)

The mites are spread from person to person through close personal contact (skin to skin), including sexual contact. They may also be spread through contact with infested clothes or bedding, although this is uncommon. Sometimes the whole family can get scabies. The spread is more likely with overcrowding and sexual promiscuity.

While the majority of cases have a relatively small number of mites (as few as 15), infestation with thousands or millions will cause the crusted condition of Norwegian scabies. Diagnosis is made on a scraping which reveals vast numbers of lesions. It may be encountered in nursing homes. Treatment is with ivermectin 200 mcg/kg (o) 2 doses, 7 days apart plus topical treatment. Treatment can be difficult and may require specialist input.⁵

Treatment⁵

For all ages (except children under 6 months):

• – permethrin 5% cream (treatment of choice)

  or

• – benzyl benzoate 25% emulsion (dilute with water if under 10 years)

• – best applied to clean, cool, dry skin

• Apply to entire body from jawline down (including under nails, in flexures and genitals).

• Leave permethrin overnight, then wash off thoroughly.

• Leave benzyl benzoate for 24 hours.

• Avoid hot baths or scrubbing before application.

• Treat the whole family at the same time even if they do not have the itch.

• Wash clothing, any soft toys and bedclothes as usual in hot water and hang in sun.

• One treatment is usually sufficient but repeat scabicide treatment in 1 week for moderate and severe infections.

• For children less than 6 months use sulphur 5% cream daily for 2–3 days or crotamiton 10% cream daily for 3–5 days.

Dermatitis herpetiformis

This extremely itchy condition is a chronic subepidermal vesicular condition in which the herpes simplex-like vesicles erupt at the dermo-epidermal junction. The vesicles are so pruritic that it is unusual to see an intact one on presentation.

Some consider that it is always caused by a gluten-sensitive enteropathy. Most patients do have clinical coeliac disease.

Clinical features

• Most common in young adults

• Vesicles mainly over elbows and knees (extensor surfaces)

• Also occurs on trunk, especially buttocks and shoulders (see FIG. 120.4)

• Vesicles rarely seen by doctors

• Presents as excoriation with eczematous changes

• Masquerades as scabies, excoriated eczema or insect bites

• Typically lasts for decades

• Associated with gluten-sensitive enteropathy

• Skin biopsy and immunofluorescence show diagnostic features

Treatment

• Gluten-free diet, which may suppress the condition but is slow to take effect.

• Dapsone 50 mg (o) daily, increasing up to 200 mg (o) daily with caution (usually dramatic response). Consider expert care.

Lichen planus

Lichen planus is an epidermal inflammatory disorder of unknown aetiology characterised by pruritic, violaceous, flat-tipped papules, mainly on the wrists (see FIG. 120.5) and legs. If in doubt, diagnosis is confirmed by biopsy. One differential diagnosis is a lichen planus-like drug eruption (e.g. antihypertensives, anti-malarials).

Clinical features

• Young and middle-aged adults

• 4Ps—papule, purple, polygonal, pruritic

• Small, shiny, lichenified plaques

• Symmetrical and flat-tipped

• Violaceous

• Flexor surfaces: wrists, forearms, groin, ankles

• Can affect oral mucosa—lacy white streaks (Wickham striae) or papules or ulcers

• Can affect nails, scalp and genital mucosa

Management

• Explanation and reassurance

• Cutaneous lichen planus usually resolves over 6–9 months, leaving discoloured marks without scarring

• Recurrence rare

• Asymptomatic lesions require no treatment

• Topical moderate to very potent corticosteroids (may use occlusive dressing)

• Oral prednisolone if not successful

• Intralesional corticosteroids for hypertrophic lesions

• Consider referral for expert advice

Pruritus ani

The generalised disorders causing pruritus may cause pruritus ani. However, various primary skin disorders such as psoriasis, dermatitis, contact dermatitis and lichen planus may also cause it, in addition to local anal conditions. It is covered in more detail in CHAPTER 36.

Pruritus capitis (itchy scalp)⁷

Scalp pruritus may be caused by several common skin conditions including seborrhoeic dermatitis, atopic dermatitis, psoriasis, tinea capitis, lichen simplex chronicus, contact dermatitis and pediculosis. Look for evidence of these conditions in the scalp and treat accordingly. The less severe form of seborrhoeic dermatitis is known as pityriasis capitis or dandruff.

Pruritus vulvae

Refer to CHAPTER 107.

Tinea cruris

Also known as Dhobie itch and jock itch, tinea cruris is a common infection of the groin area in young men (see FIG. 120.6), usually athletes, that is commonly caused by a tinea infection, although there are other causes of a groin rash (see TABLE 120.4). The dermatophytes responsible for tinea thrive in damp, warm, dark sites. The feet should be inspected for evidence of tinea pedis. It is transmitted by towels and other objects, particularly in locker rooms, saunas and communal showers.

Clinical features

• Itchy rash

• More common in young males

• Strong association with tinea pedis (athlete’s foot)

• Usually acute onset

• More common in hot months—a summer disease

• More common in physically active people

• Related to chafing in groin (e.g. tight pants, and especially synthetic jock straps)

• Scaling, especially at margin

• Well-defined border (see FIG. 120.7)

If left untreated, the rash may spread, especially to the inner upper thighs, while the scrotum is usually spared. Spread to the buttocks indicates T. rubrum infection.

Diagnostic aids

• Skin scrapings should be taken from the scaly area for preparation for microscopy (see CHAPTER 119).

• Wood’s light may help the diagnosis, particularly if erythrasma is suspected.

Management

• Fastidious drying of skin folds.

• Apply topical terbinafine 1% cream or gel once or twice daily for 7–14 days or an imidazole topical preparation (e.g. miconazole or clotrimazole cream).

• Apply tolnaftate dusting powder bd when almost healed to prevent recurrence.

• If itch is severe, a mild topical hydrocortisone preparation (additional) can be used.⁵

• For persistent or recurrent eruption, use oral terbinafine for 2–4 weeks or griseofulvin for 6–8 weeks.

Candida intertrigo

Candida albicans superinfects a simple intertrigo and tends to affect patients with predisposing factors (e.g. broad-spectrum antibiotic therapy, diabetes, general debility, immune incompetence, obesity, immobility).

Clinical features

• Erythematous, macerated rash

• Occurs in flexures, submammary area and other skin folds

• Less well-defined margin than tinea (see FIG. 120.8)

• Associated satellite lesions and whitish discharge

• Yeast may be seen on microscopy

Treatment⁵

• Treat predisposing factors where possible.

• Apply an imidazole preparation such as miconazole 2% or clotrimazole 1%, twice daily for 2 weeks.

• Use short-term hydrocortisone cream for itch or inflammation (long-term aggravates the problem).

Erythrasma

Erythrasma, a common and widespread chronic superficial skin infection typically in a skin fold, is caused by the bacterium Corynebacterium minutissimum, which can be diagnosed by coral pink fluorescence on Wood’s light examination. Itch is not a feature.

Clinical features

• Superficial reddish-brown scaly patches

• Enlarges peripherally

• Mild infection but tends to chronicity if untreated

• Coral pink fluorescence with Wood’s light

• Common sites: groin (especially men), axillae, submammary, toe webs (see FIG. 120.9)

Treatment

• Topical imidazole e.g. miconazole or erythromycin 2% gel

• Oral roxithromycin or erythromycin

• Loose fitting clothing and antibacterial wash may prevent recurrence

Asteatotic eczema (winter itch)

This often unrecognised problem, which can be very itchy, is a disorder of the elderly. It is a form of eczema that typically occurs on the legs of the elderly (see FIG. 120.10), especially if they are subjected to considerable scrubbing and bathing. Other predisposing factors include low humidity (winter, central heating) and diuretics. The problem may be associated with a malabsorption state, hypothyroidism or drugs e.g. statins, diuretics.

Clinical features

• Dry skin

• Fine scaling and red superficial cracking

• ‘Crazy paving’ appearance

• Occurs on legs, especially shins

• Also occurs on thighs, arms and trunk

Treatment

Based on correcting dry skin:⁸

• Quick, cool showers (<2–3 minutes)

• Use soap-free substitutes in the shower

• Liberal use of emollients on damp skin, after the shower

• Avoid excessive heating in winter

• Avoid use of electric blankets

• Apply topical steroid diluted in white soft paraffin to reddened skin

‘Golfer’s vasculitis’ (summer leg rash)⁹

This is a term used to describe an erythematous pruritic rash that appears on the legs after prolonged exercise such as golf or hiking, usually during summer months.

The rash is a red, blotchy, flat to slightly raised eruption on the lower leg. It is more common over age 50. It usually clears spontaneously within 3 days.

Brachioradialis pruritus

In this condition, itch and discomfort are limited to the outer surface of the upper limb above and below the elbow. It is often associated with sun damage, xerosis and nerve entrapment, hence the term ‘golfer’s itch’.²

Grover disease

Also known as transient acantholytic dermatosis, Grover disease produces small, firm, intensely pruritic, reddish-brown, warty papules with minimal scale, mainly on the upper trunk. It usually occurs in middle-aged to elderly men (typically 70–80 years). Trigger factors include heat, sweating, fever and occlusion, especially on photo-damaged skin. Diagnosis is by biopsy. Treatment is to relieve the itch until spontaneous resolution occurs. Effective treatments include topical (preferable) or oral corticosteroids and ultraviolet light.³

Cercarial dermatitis

Cercarial dermatitis (swimmer’s itch) is an acute allergic dermatitis caused by contact with schistosomes in warm freshwater lakes. Skin under swimwear is often protected.

Nodular prurigo (prurigo nodularis)

These are extremely pruritic firm lumps about 1–3mm in diameter that erupt on the arms, legs and trunk. They can affect all ages and may manifest in late pregnancy. Definite diagnosis is with skin biopsy. They tend to run a long course and are difficult to treat.

Lichen simplex

Lichenification is a form of dermatitis caused by repeated scratching or rubbing, which results in epidermal thickening. Lichen simplex is the term used when no primary dermatological cause can be found.

Urticaria⁵

Urticaria is a common condition that mainly affects the dermis. It can be classified as acute (minutes to weeks) or chronic (lasting more than 6 weeks). It can also be classified as diffuse weal-like or papular (hives).

The three characteristic features of diffuse urticaria are:

• transient erythema, often with central pallor

• transient oedema

• transient intense itch

The most common causes are infections, especially viral URTIs, drug allergies and IgE-mediated food reactions.

Classification according to site

1. Superficial: affecting superficial dermis = urticaria; occurs anywhere on body, especially the limbs and trunk.

2. Deep: affecting subcutaneous tissue = angio-oedema; occurs anywhere but especially peri-orbital region, lips and neck.

Checklist of causes³

• Infections: viruses (the most common cause in children), bacteria (especially streptococcus infection), parasites, protozoa, yeasts

• C₁ esterase inhibitor deficiency (hereditary angio-oedema)—recurrent unexplained episodes of angio-oedema

• Allergies (acute allergic urticaria is dramatic and potentially very serious):

  • – azo dyes

  • – drugs: penicillin and other antibiotics

  • – foods: eggs, fish, cheese, tomatoes, others

• Pharmacological:

  • – drugs: penicillin, aspirin, codeine

  • – foods: fish, shellfish, nuts, strawberries, chocolate, artificial food colourings, wheat, soy beans

  • – plants: nettles, others

• Systemic lupus erythematosus

• Physical:

  • – cholinergic: response to sweating induced by exercise and heat (e.g. young athletes)

  • – heat, cold, sunlight

• Insect stings: bees, wasps, jellyfish, mosquitoes

• Pregnancy (last trimester), other hormonal

• Unknown (idiopathic)—80%; possible psychological factors

Investigations for chronic urticaria

• Full blood examination—look for eosinophilia of parasites

• ANA and DNA binding tests—consider SLE

• Skin prick tests

Treatment⁵

• Avoid any identifiable causes.

• Avoid salicylates and related food preparations (e.g. tartrazine).

• Consider elimination diets.

• Use oral antihistamines (e.g. cyproheptadine) or a less sedating one (e.g. cetirizine, loratadine, fexofenadine).

• Consider adding an H₂ antagonist (e.g. ranitidine 150 mg bd).

• Systemic corticosteroids (e.g. prednisolone 50 mg once daily) can relieve acute urticaria but should be avoided as high doses are required and symptoms usually return once treatment stops.⁵

• For severe urticaria with hypotension and anaphylaxis give IM adrenaline.⁵

• Use topical soothing preparation if relatively localised (e.g. crotamiton 10%, or phenol 1% in oily calamine or menthol 1% cream).

• Lukewarm baths with Pinetarsol or similar soothing bath oil.

Papular urticaria

This is a hypersensitivity to insect bites or insects in the environment, particularly seen in children aged 2–6 years. The lesions are grouped together, often as clusters of very itchy papules.

Common urticaria tends to come and go within hours but the lesions of papular urticaria persist.

The treatment for insect bites includes antipruritics and topical corticosteroids, e.g. betamethasone dipropionate 0.05% ointment or cream tds until resolved.

Flea bites

Fleas (see FIG. 120.11) cause itchy erythematous maculopapular lesions. They are usually multiple or grouped in clusters, occurring typically on the arms, forearms, leg and waist (where clothing is tight). Treat the source of infestation, particularly domestic cats and dogs. The itchy bites can be treated with an application of simple agents such as Stingose, alcohol, damp soap, anti-itch cream or a mild corticosteroid ointment.

Bed bug bites¹⁰

The common bed bug (Cimex lectularius, see FIG. 120.12) is now a major problem related to international travel. It travels in baggage and is widely distributed in hotels, motels and backpacker accommodation. The bugs hide in bedding and mattresses. Clinically bites are usually seen in children and teenagers. The presentation is a linear group of three or more bites (along the line of superficial blood vessels), which are extremely itchy. They appear as maculopapular red lesions with possible wheals. The lesions are commonly found on the neck, shoulders, arms, torso and legs. A bed bug infestation can be diagnosed by identification of rust-coloured specimens collected from the infested residence. In hotels and backpacker accommodation look for red specks in mattresses and check luggage.

Management

• Clean the lesions with antiseptic soap.

• Apply a corticosteroid ointment.

• A simple antipruritic agent may suffice e.g. calamine lotion.

• Call in a licensed pest controller.

Control treatment is basically directed towards applying insecticides to the crevices in walls and furniture. Be careful of used furniture and insist that mattresses are delivered in plastic coverings.

Sandfly bites

Refer CHAPTER 128.

• Lichen planus

• Dermatitis herpetiformis

• Norwegian scabies

Hand-out sheets from Murtagh’s Patient Education 7th edition:

• Bed bug bites

• Pruritus ani

• Scabies

• Urticaria (hives)