At a Glance - Erythema annulare centrifugum versus Lyme disease

Contributed by Dr Jean Watkins, a retired GP in Hampshire

Erythema annulare centrifugum: polycyclic plaques
Erythema annulare centrifugum: polycyclic plaques

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).

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