Clinical Geriatrics

Case Presentation
A 63-year-old woman presented in June complaining of a 1-week history of malaise, headache, generalized body aches, and low-grade fever of 101 degrees F. She denied any upper respiratory, gastrointestinal, or other associated symptoms. Physical examination was generally unremarkable with the exception of a slightly raised, 8 x 6–cm, irregular, ovoid patch with spotty areas of mildly intense-to-faded erythema found on her right anterior thigh (Figure 1). A central papule was noted, consistent with a punctum from a recent tick or insect bite (Figure 2). When the lesion was pointed out to the patient, she remembered that it had been present for several days. She described the skin lesion as mildly pruritic, slightly tender, and slowly expanding. On further questioning, the patient recalled removing a small insect from her leg—possibly a tick—the week before while gardening. Her house borders a large city park in Pennsylvania, and deer sightings are frequent.

Discussion
The rash depicted represents primary erythema migrans (EM), a dermatologic manifestation of early Lyme disease (LD). The differential diagnosis includes tinea corporis, pityriasis rosea, granuloma annulare, urticaria, eczematoid dermatitis, insect bite, cellulitis, and allergic contact dermatitis.

In the United States, LD is caused by the spirochete Borrelia burgdorferi, which is transmitted through the bite of the Ixodes scapularis tick. LD is associated with a variety of signs and symptoms that may reflect different stages of infection. The stages include early localized (stage 1), early disseminated (stage 2), and late chronic (stage 3). Most patients (70-80%) develop the early localized form of LD, which is characterized by the presence of EM and flu-like symptoms.¹ Primary EM occurs at the site of a tick bite and typically presents as a slowly expanding erythematous patch. EM lesions may have central clearing, classically described as a bull’s eye or target-like appearance. However, more commonly, EM lesions are homogenously erythematous and lack central clearing (Table I).² EM lesions typically expand to 5 cm or more in diameter, and tend to be mildly tender or pruritic.

Various atypical EM lesions have been reported, including lesions with vesicles, erythematous papules, central edema, ulceration, purpura, lymphangitic streaking, alopecia, and desquamation.^2,3 Variation in EM appearance may be the result of variations in host response, inoculum size, or differences in borrelia species.^2,3 In the elderly population, atypical and often subdued presentations of cutaneous diseases are common, as there is decreased dermal vascularity and cellularity in aging skin, as well as a decline in immune responsiveness with aging.^4,5 Such factors may have influenced the faded appearance of EM in the patient described above.

EM lesions typically develop 7-10 days after a tick bite, with a reported range of 1 to 32 days.² Lesions that occur while the Ixodes tick is still attached or develop within 48 hours of tick detachment are likely to be local hypersensitivity reactions to the tick bite, and not EM.⁶ Early LD is usually accompanied by nonspecific, flu-like symptoms including myalgias, arthralgias, fatigue, headache, neck stiffness, and sometimes fever.