Asymptomatic Petechial Eruption on the Lower Legs

Gary Mendese, MD; Donald Grande, MD
Mystic Valley Dermatology, Stoneham, Massachusetts

Disclosure: The authors report no relevant conflicts of interest.

The authors report an unusual case of Rocky Mountain spotted fever that presented as an asymptomatic petechial eruption on the lower legs. Rocky Mountain spotted fever is rare in New England and, as such, is typically not on the differential diagnosis when presented with such patients. What began as an asymptomatic eruption progressed to more classic signs of the disease, including a positive Rocky Mountain spotted fever titer. The patient was successfully treated with doxycycline and within a short period of time, was completely back at baseline.
(J Clin Aesthet Dermatol. 2013;6(9):48–49.)

A 70-year-old woman from Massachusetts presented with a two-day history of an asymptomatic petechial eruption on the ankles and distal shins. She was in excellent health and denied daily medications. There were no associated systemic symptoms and she denied any recent travel except for a recent vacation to Vermont. She denied any recent arthropod bites or new environmental exposures.

Examination revealed numerous small 2 to 3mm palpable petechiae solely on the distal lower extremities, ankles, and feet (Figure 1). Physical examination findings were otherwise unremarkable; no lymphadenopathy was seen and a thorough review of systems was unremarkable.

A punch biopsy specimen was taken for histologic examination (Figure 2). The histopathologic examination of the biopsy specimen revealed superficial and deep perivascular inflammation with numerous extravasated erythrocytes without evidence of vasculitis. This was deemed to be most consistent with a purpuric generalized cutaneous hypersensitivity reaction. Results from a complete blood count, erythrocyte sedimentation rate, extensive chemistry panel, and liver function tests revealed normal findings.

Cerebrospinal fluid analysis revealed elevated protein at 60.8mg/dL (normal=15–-45mg/dL), but was otherwise unremarkable. Lyme immunoglobulins were undetectable (<1U/mL), and anti-nuclear and P and C anti-neutrophil cytoplasmic antibody titers were negative (<1:20). However, the patient’s Rocky Mountain spotted fever (RMSF) immunoglobulin G titer was positive and a diagnosis of RMSF was made.

The patient, initially asymptomatic, presented with severe headache and spiking fevers, prompting an inpatient workup. She was started on empiric doxycycline, which was continued for 14 days after her RMSF titer returned positive. Within three days, her fevers and headache subsided and by one week, her petechial eruption virtually disappeared.

RMSF, caused by Rickettsia rickettsii, is considered to be the most severe tick-borne illness in the United States.[1] Originally discovered in the northern Rocky Mountains, its presence has been reported in virtually every state, except for Vermont and Hawaii.[2] This gram-negative, obligate intracellular bacteria is transmitted by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and brown dog tick (Rhipicephalus sanguineus). The incubation period of RMSF is anywhere from 1 to 14 days.[3] Symptom onset can be gradual or, as with our patient, quite abrupt.

The classic triad of fever, rash, and headache is present in approximately half of cases, but the characteristic petechial rash is present in greater than 90 percent of patients.[1] Initially blanchable, the rash typically begins on the extremities and then quickly spreads to the trunk and face, becoming petechial or purpuric after 6 to 8 days.[4]

Central nervous system involvement is present in as many as one-third of cases and can manifest as headache, confusion, and lethargy, but can also progress to stupor, seizures, and even coma.[5]

The workup for RMSF can reveal somewhat nonspecific findings, including a mild transaminitis, leukocytosis, and thrombocytopenia.[4] Diagnosis is confirmed based on indirect immunofluorescent antibody tests, serology, enzyme immunoassay, or latex agglutination.[4] Skin biopsy is not well described in any large series and findings are somewhat variable, showing frank vasculitis in the majority of cases in one small series.[6]

Prompt treatment with doxycycline is indicated, even before receipt of confirmatory diagnostics. Early antibiotic therapy reduces the mortality rate from 20 percent in untreated patients down to only five percent.[7]

It is uncertain whether the patient described in this case acquired RMSF from Massachusetts or Vermont, to where she traveled shortly before symptom onset. Irrespective of etiology, the authors submit that RMSF should be considered in any patient with unexplained petichiae regardless of the state of origin.

1.    Graham J, Stockley K, Goldman R. Tick-borne illnesses, a CME update. Pediatr Emer Care. 2011;27:141–150.
2.    Rocky mountain spotted fever. Accessed on September 30, 2011.
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4.    Helmink CG, Bernard KW, D’Angelo LJ. Rocky mountain spotted fever: clinical, laboratory and epidemiological features of 262 cases. J Infect Dis. 1984;150:480–488.
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6.    Kao GF, Evancho CD, Ioffe O, et al. Cutaneous histopathology of Rocky Mountain spotted fever. J Cutan Pathol. 1997;24(10):604–610.
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