SAEM Clinical Images Series: An On-Target Diagnosis
A 25-year-old female with no pertinent past medical history presented to an emergency department in Massachusetts with four days of generalized malaise, myalgias, congestion, low-grade fever, and a rash behind her left knee. The patient denied cough, shortness of breath, chest pain, abdominal pain, nausea, vomiting, and diarrhea. She lives with three roommates, none of whom were sick, and she denied any other known sick contacts. She also denied any occupational exposures or recent travel, although did endorse some recent hiking in the area.
Vitals: BP 128/84; HR 88; Temp 98°F; RR 18; SpO2 (on RA) 100% General: Well appearing HEENT: No conjunctival injection Cardiovascular: S1, S2; no murmurs, rubs, or gallops Skin: Erythematous patch with central clearing in left popliteal fossa WBC: 5.1 Hgb: 12.6 Platelets: 223 Sodium: 139 Creatinine: 0.8 ALT/AST: 22/22 COVID/Influenza/RSV: negative This clinical image depicts erythema migrans (EM), the classic rash seen in 70- 80% of early localized Lyme disease infections. Lyme disease is a bacterial infection caused by the spirochete Borrelia burgdorferi, transmitted through bites from Ixodes scapularis (Blacklegged Tick). Lyme disease is endemic to the northeastern part of the United States but is also commonly reported in the upper Midwest region of the country. There are three stages of Lyme disease: early localized infection, early disseminated infection, and late disseminated infection. Early localized infection starts 3-30 days after a tick bite. This stage is characterized by the EM rash as well as fatigue, low-grade fevers, malaise, myalgias, and lymphadenopathy. EM develops at the site of the tick bite, although only 25% of patients with the characteristic rash recall being bitten by a tick. Over the next several days, the rash will expand and may develop a central clearing. Thus, the rash is often described as appearing like a “bull’s eye” or a “target.” Serological testing may be negative in early Lyme disease thus diagnosis at this stage is usually clinical. Treatment for early localized infection is typically Doxycycline 100mg PO BID x 10-14 days. Cefuroxime 500mg PO BID x 14 days is another option. Amoxicillin 500mg PO TID x 14 days is the preferred antimicrobial in patients who are pregnant and/or breast-feeding. As when treating infections caused by other spirochetes such as Treponema pallidum, a Jarisch- Herxheimer reaction may occur. Left untreated, disseminated disease will develop in 60% of patients. Most symptoms will occur within days to months, although late disseminated disease may take months to years to present. A wide range of clinical presentations are possible with early disseminated disease including diffuse annular skin lesions, meningoencephalitis, cranial nerve palsies (most commonly Bell’s Palsy), peripheral neuropathies, and AV nodal blocks. Late disseminated infection can present with transient, migratory oligoarticular arthritis and non-focal nervous system symptoms such as mild encephalopathy and fatigue. Serological studies in disseminated disease are highly sensitive and the CDC recommends two-step testing such as an enzyme immunoassay or immunofluorescent antibody assay followed by a Western blot if the initial testing is positive or equivocal. Treatment of disseminated Lyme depends on the systems involved. Given the ambiguity of early serologic testing and the potential for development of disseminated disease, erythema migrans is a clinical “can’t miss” dermatologic diagnosis in the emergency department.Take-Home Points
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Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.
