Erythema means an area of localised or, sometimes, generalised blanching redness of the skin as a result of vasodilation. It is usually caused by mechanical or physical skin injury (including radiation), infection or inflammation.
Red flag symptoms to look out for include:
Red flag symptoms
- Non-blanching in an unwell patient
- Marked systemic upset, fever or respiratory problems
- Spreading from broken skin (such as venous leg ulcers)
- Recent tick bite (especially if in a known geographical risk area for Lyme disease)
- Pregnancy
Possible causes
Reasons for acute or chronic/recurrent erythema range from obvious and simple conditions, such as localised urticarial reaction after an insect bite, through those of moderate significance, such as caloric or chemical burns of varying degrees, to potentially life-threatening situations such as anaphylaxis.
The most common possible medical causes are listed below. Note that up to 50% of occurrences of erythema have no apparent medical cause.
The most common possible medical causes are:
- Urticaria
- Lyme disease
- Liver disease
- Erythema infectiosum
- Erythema multiforme
Lyme disease
Erythema migrans develops as part of Lyme disease after infection with one of the four main Borellia species, which have geographical preferences. The incubation period may be three to 30 days after a tick bite or, possibly, after the inappropriate removal of an infective tick.
Patients may present with a large lesion (gradually expanding to up to 50cm diameter or so), often located on the limbs, which might be accompanied by other lesions elsewhere. It can have a pale ‘bull's eye’ centre and does not tend to itch or hurt, but can feel warm to the touch.
The red flag for Lyme disease is the presence of additional intermittent flu-like symptoms; body aches and swollen glands. Later on, complications including joint pains and swellings (predominantly of the knees, but the pains can shift between joints), facial palsy, limb paraesthesia, meningitis-like features or hepatitis can develop.
Prompt management with serology and antibiotic treatment according to local guidelines in at-risk cases is important.
Erythema infectiosum
Erythema infectiosum is also known as fifth disease or slapped cheek syndrome. It is caused by the human erythrovirus or parvovirus. It typically affects school-age children, with a peak occurrence in winter and spring. The majority of adults will have acquired immunity.
Erythema infectiosum may happen without really being noticed. In more obvious presentations, a bright looking rash starts on the face and spreads over the limbs, typically sparing the palms and soles (which may feel itchy).
This rash can sometimes come and go for several weeks before it fully resolves. Interestingly, the rash actually only starts at the time when the patient is already no longer contagious to others.
There is rarely any significant systemic upset, although some patients may have headaches, rhinorrhoea, a fever or an upset stomach. The condition resolves within a week by itself.
Exposure of pregnant women without immunity to the virus can be problematic. Although the chances are small, an infection can lead to an increased risk of miscarriage, foetal death (up to 10%), or chronic infection-related conditions, especially in the first 20 weeks of pregnancy.
Pregnant women with suspected infection should have a parvovirus serology and a possible referral for close ultrasound monitoring of foetal growth.
The other groups of adults at risk of complications from a late-acquired erythema infectiosum infection are patients with an impaired immune system (through an HIV infection, undergoing chemotherapy or radiotherapy, or those taking immunosuppressive drugs), or those with severe anaemia/sickle cell anaemia.
There is no method of prevention, such as a vaccination, for erythema infectiosum.
Erythema multiforme
Erythema multiforme can develop as a reaction to medications (NSAIDs, antibiotics), infections or inflammatory conditions. It is not contagious. Symptoms are usually mild but may last for several weeks.
The rash starts as red spots, which can grow into patchy lesions with a target-cell or bull's eye-type centre and a darker outer ring. The lesions can be several centimetres wide and slightly itchy or uncomfortable. There may be general malaise, fever, some sensitivity to light, skin sores and joint aches.
Erythema multiforme usually affects patients under the age of 40 years. The main, potentially life-threatening complication, Stevens-Johnson syndrome, is rare. Relevant differential diagnoses including pemphigoid, pemphigus and dermatitis herpetiformis need to be considered.
If the patient is well, treating the underlying cause and symptomatic relief with antihistamines and topical steroids might be all that is needed. Very rarely, more severe complications may occur, such as cellulitis, septicaemia, or inflammation of the liver or the lungs.
There is a possibility of a recurrence of erythema multiforme, especially if it was caused by the Herpes simplex virus, which can be reactivated.
- Dr Jacobi is a GP in York
