What is annular erythema?
Annular erythema is a descriptive term that refers to a number of chronic annular and erythematous skin eruptions. Other descriptive terms used to classify these types of lesions include:
- Erythema annulare
- Erythema annulare centrifugum
- Figurate erythema
- Erythema perstans
- Erythema gyratum perstans
- Erythema figuratum perstans.
Erythema gyratum repens is often classified separately.
What are the signs and symptoms of annular erythema?
Annular erythema may occur at any time throughout life, from infancy to old age. The eruption usually begins as a small raised pink-red spot that slowly enlarges and forms a ring shape while the central area flattens and clears. There may be an inner rim of scale. The rings enlarge at a rate of about 2–5 mm/day until they reach a diameter of about 6–8 cm. Sometimes the lesions do not form complete rings but grow into irregular shapes. One or several lesions may be present.
Annular erythema most often appears on the thighs and legs, but may occur on the face, trunk and arms. The lesions rarely cause symptoms but in some patients may cause mild itching or stinging.
What causes annular erythema?
Often no specific cause for the annular erythema is found. However, it has been noted that annular erythema is sometimes linked to underlying diseases and conditions. These include:
- Bacterial, fungal and viral infections such as tuberculosis, secondary syphilis, sinusitis, candidiasis or tinea
- Drugs including chloroquine and hydroxychloroquine, oestrogen, penicillin and amitriptyline
- Food, most often blue cheese or tomatoes
- Recurrent or chronic appendicitis
- Cholestatic liver disease (blocked bile system)
- Graves disease (overactive thyroid gland).
In these situations, the annular erythema resolves once the underlying cause is treated or the causative drug is stopped.
How is the diagnosis of annular erythema made?
The diagnosis of annular erythema is made clinically and may be confirmed by histopathology, which shows a perivascular lymphocytic infiltration.
Further investigations may be carried out to exclude other causes of annular rashes and to look for an underlying cause if any.
Differential diagnosis of annular erythema includes:
- Erythem gyratum perstans, a paraneoplastic eruption associated with underlying malignancy in which there are concentric and whirling rings
- Erythema migrans (Lyme disease)
- Target lesions in erythema multiforme
- Annular plaques with central blisters in fixed drug eruption and bullous pemphigoid
- Serpiginous plaques in cutaneous larva migrans
- Annular dermal plaques in granuloma annulare and in one form of lichen planus
- Annular scaly plaques in discoid eczema, chronic plaque psoriasis, seborrhoeic dermatitis, pityriasis rosea, discoid lupus, porokeratosis, and tinea (dermatophyte infection)
- Annular smooth, urticated lesions in urticaria, Sweet syndrome, polymorphous light eruption, subacute cutaneous lupus erythematosus and systemic lupus erythematosus.
What is the treatment of annular erythema?
Annular erythema usually clears up by itself. Eruptions may last for a few weeks to many years (the average duration is 11 months). Most cases of annular erythema require no treatment (and no curative therapy is known). However, topical corticosteroids may be helpful in reducing redness, swelling and itchiness.