Derm Dx: An erythematous annular plaque with central clearing

Lyme disease is a multisystem infection caused by the spirochete, Borrelia burgdorferi. The Ixodes tick vector becomes infected from feeding on an infected white-tailed deer or white-footed mouse host. B. burgdorferi  is then transmitted to the human host via the...

Submit your diagnosis to see full explanation.

Lyme disease is a multisystem infection caused by the spirochete, Borrelia burgdorferi. The Ixodes tick vector becomes infected from feeding on an infected white-tailed deer or white-footed mouse host. B. burgdorferi  is then transmitted to the human host via the saliva of the Ixodes vector. Transmission is most likely after 48 hours of tick attachment.

Lyme disease occurs worldwide but primarily affects people in the United States and Europe. In the United States the majority of the Lyme disease cases are reported from the Northeast and western Wisconsin.

Both tick vector and the B. burgdorferi species vary by geographic region. In the western United States the tick vector species is I. pacificus and in the eastern United States and Great Lakes regions the disease is transmitted by I. scapularis.  In the United States, B. burgdorferi causes most cases of Lyme disease. However, most cases in Europe are caused by B. garinii and B. afzelii.

Most Lyme disease cases occur from May to November. More than 80% of cases in the northern hemisphere occur in the summer months of June through August. There is no gender predilection. The majority of patients are aged 20 to 50 years.

There are three clinical stages of Lyme disease: early localized disease, early disseminated disease and chronic disease. Patients with early localized disease experience influenza-like symptoms including malaise, anorexia, nausea, fatigue, headache, arthralgias, myalgias and fever. They may also experience lymphadenopathy, diffuse urticarial, malar erythema, conjunctivitis or hepatitis. 

Classic presentation of early Lyme disease consists of erythema migrans, which affects 60% to 90% of patients with B. Burgdorferi.  Approximately seven to 15 days after the tick detaches from the host a single erythematous expanding annular plaque with central clearing appears, resembling a bull’s eye. The advancing edge may also be vesicular or crusted. Typically, the lesions are greater than 5 cm in diameter and appear on the trunk, axilla, groin and popliteal fossa, and last for up to six weeks in untreated patients.

Although erythema migrans usually appears as a solitary lesion, 20% to 25% of patients present with multiple lesions from either multiple tick bites or disseminated disease. The lesions in patients with disseminated disease are usually smaller and appear several days to weeks after the primary erythema migrans.  

Histologically, erythema migrans is usually nonspecific; however it is common to find superficial and deep perivascular infiltrate with eosinophils and plasma cells and apoptotic keratinocytes in the epidermis. The Warthin-Starry stain may also detect Borrelia organisms.

The majority of untreated patients with erythema migrans progress to develop early disseminated disease — 60% develop arthritis, 10% develop neurologic involvement (usually facial nerve palsy) and 5% develop cardiac involvement (typically atrioventricular block).

Some patients who progress to chronic disease experience chronic arthritis (10%) and neurological complications such as encephalopathy, encephalomyelitis and neuropathy.

In Europe, 10% patients with chronic disease may also develop acrodermatitis chronica atrophicans (ACA) or primary diffuse atrophy. ACA is uncommon in the United States, as it is associated with the European spirochete B. afzelii. 

In the southern New England region of the United States approximately 10% of patients with Lyme disease are coinfected with babesiosis and may present with more severe influenza-like symptoms.

Diagnosis & Treatment

Lyme disease cases are defined as confirmed, probable or suspected. A confirmed case of Lyme disease is defined by the presence of erythema migrans, plus either exposure to the Ixodes tick or confirmatory laboratory evidence, most commonly serologic testing.

Early Lyme disease diagnosis is made clinically based on the presence of erythema migrans, which is the most sensitive clinical finding of Lyme disease. Serologic testing is often negative in the 14 days after infection, but among patients whose symptoms last longer than 14 days, anti-Borrelia antibodies can be detected using enzyme-linked immunosorbent assay (ELISA) followed by Western blot. Nonspecific laboratory findings include anemia, an elevated sedimentation rate (50% of patients), an elevated immunoglobulin M (IgM) level, and elevated liver function tests (20%).

The treatment of choice for Lyme disease in adults is doxycycline 100 mg twice daily for 14 to 21 days. Children aged younger than 8 years and pregnant women are treated with amoxicillin 500 mg every eight hours for 14 to 21 days. Parenteral penicillin G or ceftriaxone are used in pregnant patients with disseminated Lyme disease.

Patients living in western Wisconsin and New England should be counseled on preventive tick-control measures, such as wearing long clothing and inspecting for ticks after spending time outdoors. Patients living in endemic areas who experience Ixodes tick attachment for more than 36 hours can be given prophylaxis with a single dose of 200 mg of doxycycline within 72 hours of tick detachment.

The patient in this case was treated with doxycycline 100 mg twice daily for 21 days. She experienced complete resolution of symptoms and erythema migrans. She has not developed additional sequelae of Lyme disease.

Lauren Brin, BA, is a senior medical student at Creighton University School of Medicine in Omaha, Nebraska.

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.