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A White male presented with a purulent erythematous edematous plaque with central necrosis and ulceration on his right flank

A 65-year-old White male presented with a 1-week history of a painful, purulent, erythematous edematous plaque with central necrosis and ulceration on his right flank. The patient did not recall anything biting him, nor did he see anything on his skin. He had flulike symptoms and a headache. He was seen at the emergency room and was given a dose of Bactrim and Keflex empirically.

What's your diagnosis?

Pyoderma gangrenosum

Erythema chronicum migrans

Brown recluse spider bite


Granuloma annulare

Erythema chronicum migrans (ECM) is the classical dermatologic manifestation of Lyme disease, a condition caused by Borrelia burgdorferi, a bacterial spirochete. Lyme disease is the most commonly transmitted tick-borne illness in the United States. This infection is typically transmitted through a bite by the Ixodes tick commonly found in the Midwest, Northeast, and mid-Atlantic regions; however, the geographical distribution continues to expand over time in the United States. Ticks must be attached for 24-48 hours to transmit the pathogen. There are three general stages of the disease: early localized, early disseminated, and late disseminated.

Dr. Donna Bilu Martin, Premier Dermatology, MD, Aventura, Fla.

Dr. Donna Bilu Martin

The most common presentation is the early localized disease, which manifests between 3 and 30 days after an infected tick bite. Approximately 70%-80% of cases feature a targetlike lesion that expands centrifugally at the site of the bite. Most commonly, lesions appear on the abdomen, groin, axilla, and popliteal fossa. The diagnosis of ECM requires lesions at least 5 cm in size. Lesions may be asymptomatic, although burning may occur in half of patients. Atypical presentations include bullous, vesicular, hemorrhagic, or necrotic lesions. Up to half of patients may develop multiple ECM lesions. Palms and soles are spared. Differential diagnoses include arthropod reactions, pyoderma gangrenosum, cellulitis, herpes simplex virus and varicella zoster virus, contact dermatitis, or granuloma annulare. The rash is often accompanied by systemic symptoms including fatigue, myalgia, headache, and fever.

The next two stages include early and late disseminated infection. Early disseminated infection often occurs 3-12 weeks after infection and is characterized by muscle pain, dizziness, headache, and cardiac symptoms. CNS involvement occurs in about 20% of patients. Joint involvement may include the knee, ankle, and wrist. If symptoms are only in one joint, septic arthritis is part of the differential diagnosis, so clinical correlation and labs must be considered. Late disseminated infection occurs months or years after initial infection and includes neurologic and rheumatologic symptoms including meningitis, Bell’s palsy, arthritis, and dysesthesia. Knee arthritis is a key feature of this stage. Patients commonly have radicular pain and fibromyalgia-type pain. More severe disease processes include encephalomyelitis, arrhythmias, and heart block.

ECM is often a clinical diagnosis because serologic testing may not be positive during the first 2 weeks of infection. The screening serologic test is the ELISA, and a Western blot confirms the results. Skin histopathology for Lyme disease is often nonspecific and reveals a perivascular infiltrate of histiocytes, plasma cells, and lymphocytes. Silver stain or antibody testing may be used to identify the spirochete. In acrodermatitis chronica atrophicans, late Lyme disease presenting on the distal extremities, lymphocytic and plasma cell infiltrates are present. In borrelial lymphocytoma, a dense dermal lymphocytic infiltrate is present.

The standard for treatment of early localized disease is oral doxycycline in adults. Alternatives may be used if a patient is allergic or for children under 9. Disseminated disease may be treated with IV ceftriaxone and topical steroids are used if ocular symptoms are involved. Early treatment is often curative.

This patient’s antibodies were negative initially, but became positive after 6 weeks. He was treated empirically at the time of his office visit with doxycycline for 1 month.

This case and the photo were submitted by Lucas Shapiro, BS, of Nova Southeastern University College of Osteopathic Medicine, Fort Lauderdale, Fla., and Susannah Berke, MD, Three Rivers Dermatology, Coraopolis, Pa. The column was edited by Donna Bilu Martin, MD.

Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at To submit a case for possible publication, send an email to


Carriveau A et al. Nurs Clin North Am. 2019 Jun;54(2):261-75.

Skar GL and Simonsen KA. Lyme Disease. [Updated 2023 May 31]. In: “StatPearls” [Internet]. Treasure Island, Fla.: StatPearls Publishing; 2023 Jan.

Tiger JB et al. J Am Acad Dermatol. 2014 Oct;71(4):e133-4.

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