Erythema annulare centrifugum
Aetiology
Associated with:
- Bacterial infections: Escherichia coli, streptococcus or mycobacteria.
- Fungal infections: dermatophytes, candida or pityrosporum.
- Lice or roundworm.
- Viral infections.
- Drugs: estrogens, cimetidine, penicillin, salicylates, antimalarials, amitriptyline.
- Blue cheese and tomatoes.
- Malignancy.
- Liver disease, sarcoidosis.
Presentation
- Can occur at any age.
- Rash usually occurs on the lower limbs. Initially one or more erythematous papules.
- Lesions grow into annular, polycyclic plaques that spread outwards, clearing at centre, often with a rim of scale. Asymptomatic or itching.
Investigations
- Skin scraping to exclude fungal infection. Skin biopsy.
- FBC and LFTs will indicate infection and liver problems.
- ELISA and western blot tests to exclude Lyme disease.
- ANA test to exclude systemic lupus erythematosus.
- Stool specimen if parasitic worms suspected.
- Chest X-ray might indicate TB, sarcoidosis or lymphoma.
Management
- Usually self-limiting, clearing in weeks, but may last for years.
- No other treatment required but topical steroids help itching and inflammation.
Lyme disease
Lyme disease: remove the tick
Aetiology
- The bacterium Borrelia burgdorferi borne by infected ticks, often carried by deer.
- Infection may remain localised or disseminate around body.
Presentation
- Localised disease: seven to 10 days after initial tick bite, erythema migrans develops and lymph glands enlarge.
- Annular erythematous patch, up to about 7cm in diameter, sometimes with central clearing or purpura.
- Disseminated Lyme disease: multiple patches of erythema migrans. Causes headache, fever, paraesthesia, facial paralysis, lymphadenopathy.
- Late Lyme disease causes arthritis, confusion, vertigo, increasing paraesthesia.
Investigations
- Diagnosis possible on history of tick bite, erythema migrans and increasing symptoms.
- Blood tests may become positive after one month.
Management
- Early treatment shortens duration.
- Remove ticks immediately and seek advice early.
- Doxycycline 200mg (72 hours after bite).
- For late complications try 30 days of doxycycline. Can also use amoxicillin, cefuroxime or azithromycin. IV antibiotics can be used in severe cases.
- Prevention (long trousers, insect repellents and so on).
