Practice scenario: Generalised, widespread rash

Key points

• Generalised rash is very common and there are multiple possible causes
• Misdiagnosis is common, so good safety netting is vital.

Common causes of generalised rash

Conditions ruled out on the basis of age are not included.

Contact dermatitis: causes redness, drying of the skin and irritation, as well as possible papules and vesicles. Itching is a prominent feature and often causes the patient to scratch, which results in broken skin with subsequent weeping.

In chronic cases, the skin becomes dry and scaly and can crack and fissure. In the acute phase, lesions tend to appear rapidly, within six to 12 hours of contact and the rash tends to be well demarcated.

Common causes include cosmetics, topical medications, metal, latex, textiles, dyes, sunscreens and cement.

Discoid eczema: raised, scaly, coin-shaped itchy red/brown lesions (1-3cm in diameter) particularly affect the legs but also the arms, flanks, hips, hands and feet.

They often occur symmetrically and over time can show central clearing. More common in middle-aged people.

Drug eruption: typically, a maculopapular rash is seen and often affects the face, hands and feet. Can be caused by a number of medicines but particularly allopurinol, beta-lactam antibiotics, sulfonamides, anticonvulsants, ACE inhibitors, non-steroidal anti-inflammatory drugs, hypoglycaemics and thiazide diuretics. 

Folliculitis: can be due to infection, occlusion, irritation or skin disease. Often seen when hairs regrow following activities such as waxing or shaving. Multiple small pustules localised to hair follicles is the typical presentation.

Insect bites: itching papules, often intense, is the hallmark symptom. Occasionally, these blister as a result of scratching. Bites tend to be in groups, are asymmetrical and occur on exposed areas.

Plaque psoriasis: characteristic salmon-pink round or oval lesions with silvery-white scales and well-defined boundaries. On darker skin, this colour is not apparent.

Typically affects elbows, knees, scalp, central trunk, umbilicus, genitalia, lower back or gluteal cleft, often symmetrically distributed.

If the scales on the surface of the plaque are gently removed, it will reveal pinpoint bleeding points from the superficial dilated capillaries. This is known as the Auspitz sign and is diagnostic.

Scabies: severe generalised pruritus, especially at night, is the hallmark symptom. Lesions are typically seen on wrists, interdigital spaces of the fingers and extensor aspects of limbs as well as penile and scrotal skin in men and beneath the breasts and nipples in women.

The rash typically shows small red papules, and the surrounding skin is often sore and damaged due to itching. 

Seborrhoeic dermatitis: characterised by a history of intermittent skin problems.

Distribution of the rash is typically symmetrical, affecting the central part of the face, scalp, eyebrows, eyelids, ears, nasolabial folds and mid-chest. The rash is red and non-itchy, with greasy-looking scales. 

Tinea corporis: usually presents as asymmetrical, itchy pink or red, scaly, slightly raised annular patches with a well-defined inflamed border, which enlarge outwards.

Over time, lesions often show central clearing. Lesions range in size and occur singly or can be numerous. 

Urticaria (or hives): round or oval lesions of variable size are discrete and confluent, raised, itchy and oedematous. They may have an erythematous border (flare) and pale centre (wheal).

Often, the patient will have a history of drug, food or substance exposure.

Atopic dermatitis: can take a variety of forms. It may continue in the school-age flexural pattern or become diffuse. Characterised by dry skin, pruritus, erythema, excoriations, scaling and lichenification.

Dermatitis herpetiformis: intense itchy clusters of papules and vesicles in a symmetrical distribution. Commonly involves the buttocks, elbows, knees, and sacral region. Most common in middle-aged men. Most patients have coeliac disease.

Lyme disease: a tick-borne condition. Typically, there is a spreading, red/purple flat rash with a defined border at the site of the bite. As the rash spreads, it develops a characteristic ‘bulls eye’ appearance. There may also be flu-like symptoms.

Lichen planus: shiny, slightly raised, pink or purple/red small lesions that may show fine white streaks (Wickham striae). Can be anywhere but mostly affects the insides of the wrists, the ankles and lower back. Itch may be absent but it usually itches, which can be severe.

Oral buccal mucosal lesions affect around 20 per cent of patients and appear as white, slightly raised lesions like a spider’s web.

Lupus (sub-acute cutaneous lupus erythematosus): raised annular lesions with central clearing, mainly on the trunk and sun-exposed areas such as face and arms. Uncommon. Mostly affects women between the ages of 20 and 50 years.

Critical diagnosis

Erythema multiforme: Lesions begin on the hands and feet before spreading up the limbs to the trunk and face. Typically precipitated by infection, it presents small, round, slightly raised red areas, some of which turn into circular lesions appearing as three concentric rings.

Oral mucosal involvement is also common, presenting as shallow white ulcers. Prodromal symptoms of fever and headache, and feeling unwell, may be present.

Useful websites

• British Association of Dermatologists: bad.org.uk/pils/discoid-eczema
• National Eczema Society: eczema.org
• Dermatology Information System (images, differential diagnoses and case reports on almost all skin diseases): dermis.net