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.
In case of an infection with the Lyme-bacterium Borrelia burgdorferi (Bb), a typical skin condition known as erythema migrans (EM) can develop at the location of the tick bite days to weeks after the tick bite.
Nearly 8,000 cases of Lyme disease have been reported in England and Wales since enhanced surveillance began in 1997. Mean annual incidence rate is now approximately 1.73 cases per 100,000 population.
Whilst Lyme disease can occur in people of all ages and gender, the peak age range affected is 45-64, followed by 24-44.
In the UK, areas where infection is acquired include Exmoor, the New Forest, the South Downs, parts of Wiltshire and Berkshire, Surrey, West Sussex, Thetford Forest, the Lake District, the North Yorkshire moors and the Scottish Highlands.
About 15% of confirmed cases are reported to have been acquired abroad and mostly by holidaymakers. The majority are acquired in the USA, France, Germany, Scandinavia and other northern and central European countries.
Recently, numbers of cases in the UK acquired in central and eastern Europe have been increasing. 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.
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.
- 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).
Where does an erythema migrans develop?
Normally at the location of he tick bite, but it can also develop at other sites, and sometimes there can be multiple at the same time, when the bacterium has disseminated (spread) throughout the body. An erythema migrans can also reappear.
How quickly does an erythema migrans arise?
Usually within a a few days to several weeks, but sometimes even after months.
How is an erythema migrans diagnosed?
If a typical erythema migrans occurs after a tick bite, then no further examination like blood tests is necessary. However, an erythema migrans can also resemble other skin conditions.
So, if no tick bite has been noticed and there is doubt about the diagnosis, then Lyme disease (Borrelia antibody) blood tests can be done. It is also possible to investigate the affected skin itself via a biopsy.
How is an erythema migrans treated?
In national treatment guidelines typically a treatment of at most 14 days with antibiotics is advised.However, some doctors advise (and treat with) 6 weeks of higher dosed antibiotic treatment in case of an erythema migrans.
Although the rash will resolve spontaneously over weeks or months, antibiotics hasten resolution and help prevent progression to Lyme disease:
- Doxycycline is the antibacterial of choice for early Lyme disease. It should be given in a dose of 100 mg twice daily for 14 days.
It is contra-indicated in children under the age of 12, and in pregnant and breast-feeding women.
- Amoxicillin (500 mg three times a day) or cefuroxime (500 mg twice a day) are alternatives if doxycycline is contra-indicated. Again, treatment should be for 14 days.
- Children under the age of 12 should have amoxicillin first-line (50 mg/kg/day in three divided doses) or cefuroxime (30 mg/kg per day in two divided doses) for 14 days.
- Macrolides such as azithromycin or clarithromycin should be reserved as third-line treatment as they are not as effective as the aforementioned antibiotics.
- 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.
Document the erythema migrans!
Take a picture of the (suspected) erythema migrans and note the date of taking the picture; circle the erythema migrans with a ballpoint pen and take another picture a few days later, so that the enlargement of the rash can be shown.
It would be best to take a photo (or photos) every day, so that the progress of the rash can be seen. Also keep notes of possible other symptoms and data that may be relevant.
Many people are bitten by a tick unnoticed and only a portion of the people who become infected will get an erythema migrans.
The erythema migrans is sometimes also difficult to see, because it is very light, or because it is hidden from the eye (like under the hair or on the back).
At the time of the appearance of an erythema migrans antibiotics should be taken immediately, without waiting for results of tests. No time should be wasted unnecessarily: the longer one is infected, the harder it is to cure.