Cos'è l'eritema cronico migrante?

Erythema chronicum migrans is a characteristic clinical feature of Lyme disease (Lyme borreliosis). It is a distinctive rash, which occurs in the majority of people infected with Borrelia burgdorferi. This infection is transmitted to humans by the bite of a tick from the genus Ixodes.

• Lyme disease is not common in the UK, with an estimated 2,000 to 3,000 new cases each year in England and Wales.

• Nel Regno Unito, le aree in cui si contrae l'infezione includono Exmoor, la New Forest, le South Downs, alcune parti di Wiltshire e Berkshire, Surrey, West Sussex, la foresta di Thetford, il Lake District, le brughiere del North Yorkshire e le Highlands scozzesi.

• Infection may also be acquired abroad and mostly by holidaymakers. The majority are acquired in the USA, France, Germany, Scandinavia and other northern, eastern and central European countries. The infection can also be found in temperate forested areas of Asia, including Russia, China and Japan.

• In Europe erythema chronicum migrans occurs as a presenting feature in up to 90% of those infected.² Presentation does appear to depend upon the Borrelia species involved; therefore, in other parts of the world the rash may be a less common presenting sign.

• The characteristic manifestation of early Lyme disease (stage 1) is erythema chronicum migrans: a circular rash at the site of the infectious tick attachment, which radiates from the bite. It can appear within 3-36 days, but typically in 7-10.

• It starts as a red macule or papule at the site of the tick bite after a (typically 7- to 10-day) delay.

• The rash is round or oval, and pink, red or purple. There is often central sparing giving a target-like appearance, and the diameter is usually larger than 5 cm. The nature of the rash and the likelihood of its presence are partly dependent on the species involved and therefore differ between continents.
  

  Eritema migrante 'a bersaglio' dell'infezione da Lyme

  

  © CDC/James Gathany, di pubblico dominio, tramite Wikimedia Commons

• Untreated, this can last for some weeks, but eventually resolves.

• Common areas include the popliteal fossa, groin, the axilla, the thorax and the trunk. The hairline and scalp are especially common in children.

• It may be associated with other symptoms of infection, including fatigue, myalgia, arthralgia, headache, fever, stiff neck, and regional lymphadenopathy.

• It may also be associated with later developments such as carditis, neurological disease, arthritis, and acrodermatitis chronica atrophicans (a swollen, bluish-red skin lesion on a distal extremity).

The National Institute for Health and Care Excellence (NICE) recommends diagnosing Lyme disease in people with erythema migrans that:⁴

• Increases in size and may sometimes have a central clearing.

• Is not usually itchy, hot or painful.

• Usually becomes visible from 1 to 4 weeks (but can appear from 3 days to 3 months) after a tick bite and lasts for several weeks.

• Is usually at the site of a tick bite.

In the absence of erythema migrans, the diagnosis of Lyme disease can be very difficult with non-specific clinical signs and symptoms that may or may not be supported by laboratory evidence.⁵

• Local tick bite reactions.

• Tinea (ringworm).

• Insect bites.

• Cellulite.

• Discoid eczema.

• Contact dermatitis.

• Urticaria.

• Eritema multiforme.

• Granuloma annulare.

• Erythema annulare centrifugum.

For anyone with erythema migrans who have no evidence of focal symptoms of Lyme disease (eg neurological, cardiac, or joint involvement), investigations are not required and start treatment with oral antibiotics (see below).

Although the rash will resolve spontaneously over weeks or months, antibiotics help prevent progression to disseminated Lyme disease.

For the treatment of Lyme disease without focal symptoms (eg, neurological, carditis) but with erythema migrans and/or non-focal symptoms, NICE recommends:

• First choice: oral doxycycline: 100 mg twice per day or 200 mg once per day for 21 days.

• First alternative: oral amoxicillin: 1 g 3 times per day for 21 days.

• Second alternative: oral azithromycin: 500 mg daily for 17 days (azithromycin should not be used to treat people with cardiac abnormalities associated with Lyme disease because of its effect on QT interval).

• Avoid exposure to tick bites.

• Remove ticks as soon as possible. Ticks take some time to transmit infection, so this may be prevented if removed quickly.

• Antibiotic prophylaxis can be offered in endemic areas under certain circumstances if the tick bite can be positively identified.