Erythema annulare centrifugum

# Overview
Erythema Annulare Centrifugum (EAC) is a descriptive term for a skin lesion consisting of redness (=erythema) in a ring form (=annulare) that spreads from the center (=centrifugum). First known to be described by Darrier in 1916. Many different terms have been used to classify these types of lesions and it is still controversial on what exactly defines EAC. Some of the types include (deep and superficial) annular erythema, erythema perstans, erythema gyratum perstans, erythema gyratum repens, darier erythema (Deep gyrate erythema & Deep gyrate erythema) and erythema figuratum perstans.

# Symptoms
Occurring at any age these lesions appear as raised pink-red ring or bullseye marks. They range in size from .5cm to 8cm. The lesions sometimes increase size and spread over time and may not be complete rings but irregular shapes. Distribution is usually on the thighs and legs but can also appear on the upper extremities, areas not exposed to sunlight, trunk or face. Currently EAC is not known to be contagious, but because many cases are incorrect diagnosed as EAC, it is difficult to be certain.

# Diagnosis
There are no specific tests that can be performed to test for EAC however tests to rule out possible more deadly diseases should be performed such as: pityriasis rosea, tinea corporis, psoriasis, nummular eczema, atopic dermatitis, drug reaction, erythema migrans and other rashes.

## Physical Examination

### Skin
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.
- Erythema annulare centrifugum. Adapted from Dermatology Atlas.

# Causes
Often no specific cause for the eruptions is found. However, it is sometimes linked to underlying diseases and conditions such as:
- Food (including blue cheese or tomatoes).
- Fungal, Bacterial and Viral infections such as sinusitis, tuberculosis, candidiasis or tinea.
- Drugs including chloroquine, hydroxychloroquine, oestrogen, penicillin and amitriptyline.
- Cancer (especially the type known as erythema gyratum perstans, in which there are concentric and whirling rings).
- Primary biliary cirrhosis.
- Graves disease.
- Appendicitis.
- Pregnancy (EAC usually disappears/stops soon after delivery of baby).
- Hormone (Contraceptive Pill, Stress, Hormone Drugs)

# Treatment
No treatment is usually needed as they usually go away anywhere from months to years. The lesions may last from anywhere between 4 weeks to 34 years with an average duration of 11 months. If there is an underlying disease then by treating and removing the disease it will stop the lesions. It usually doesn't require treatment, but topical corticosteroids may be helpful in reducing redness, swelling and itchiness.
Some supported and not supported methods of having an effect on EAC include:
- Photosensitive so it can be moved/reduced with appropriate sunlight (beware as it easy to have too much sunlight and cause sunburn).
- Vitamin D
- Immune system - hence it will increase in size/number when the immune system is low or overloaded.
- Hormone Drugs
- Disulone
- Topical calcipotriol - a topical vitamin D derivative has been known to be beneficial

# Alternative Diagnosis
- Sarcoidosis
- Fungal_infection
- Lupus_erythematosus

# Interesting Information
It is very rare and estimated to affect 1 in 100,000 per year. Because of it's rarity the documentation, cases and information is sparse and not a huge amount is known for certain, meaning that EAC could actually be a set of many un-classified skin lesions. It is known to occur at all ages and all genders equally. Some articles state that women are more likely to be affected then men.