Case Challenge: A Spreading Summertime Rash

Neil Gaffin, MD


July 13, 2018

The Rash of Lyme Disease

Borrelia burgdorferi, the agent of Lyme disease, accounts for the vast majority of infections transmitted by the Ixodes scapularis tick during the summer months. Ticks (usually the poppy seed–sized nymphs) need to be attached for at least 36 hours to transmit the organism. The earliest manifestation of the infection—generally occurring within 2 weeks at the site of the original tick bite—is erythema migrans.[1,2] Erythema migrans is typically painless and non-indurated, and often develops in anatomic locations (eg, inguinal region, popliteal fossa, axilla, and back) that are distinct from those affected by cellulitis, such as the leg or forearm. Possibly because of earlier recognition, these skin lesions are often homogeneous areas of annular erythema and lack the typical "bull's eye" appearance, considered a classic Lyme presentation.[3] Dissemination to other cutaneous locations may occur early on as well, as was seen in this patient (Figures 2-4).

Figure 2. The homogeneous erythematous rash of Lyme disease, which is more common than the classic "bull's eye" rash. Courtesy of Neil Gaffin, MD.

Figure 3. Erythema migrans behind the knee—not readily visible to the patient. Courtesy of Neil Gaffin, MD.

Figure 4. Axillary rash. Courtesy of Neil Gaffin, MD.

Diagnosis and Treatment

The diagnosis of Lyme disease rests on rash appearance in a patient presenting at the right time of year and in the right geographic location. Antibodies are detectable in only 40% of patients with erythema migrans. Serologic testing is unnecessary in patients presenting with cutaneous manifestations, because the pretest probability of Lyme disease is already high. In this case, a 10- to 14-day course of doxycycline is effective for early disease.[1,2,4] Follow-up serologic testing after completion of therapy is unnecessary.[1,2]

Consideration of coinfection with anaplasmosis should be given to patients with leukopenia and/or elevated liver function tests, and in those with persistent headache and fever despite 48 hours of treatment with either amoxicillin or cefuroxime. The benefit of doxycycline is that it treats both infections. Similarly, testing for babesiosis should be considered in patients with thrombocytopenia and anemia who have had recent exposure to endemic areas (eg, the eastern shore of Long Island, Nantucket, and Martha's Vineyard.) Finally, patients with early disease should always be counseled about the potential for reinfection and therefore the necessity of preventive measures such as daily tick checks and use of tick repellents.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as: