Infection with E chaffeensis can range in presentation from subclinical infection to life-threatening disease, as in this case. Immunosuppression, advanced age, and delay in appropriate therapy are noted risk factors for progression to more serious disease, and may have contributed to the fulminant course in this case. Presenting symptoms can be nonspecific (eg, fevers, myalgias, malaise, headache, arthralgias, cough), in addition to the symptoms noted in this patient, which included abdominal pain, nausea, vomiting, and diarrhea. Rash is infrequently noted, as are mental status changes, the latter of which was noted here.
Epidemiological clues that can suggest the diagnosis of E chaffeensis infection or the similar presenting Anaplasma phagocytophilum infection include known tick exposure or outdoor exposure in states with high incidence of disease (including Missouri, Oklahoma, Tennessee, Arkansas, and Maryland for E chaffeensis and Rhode Island, Connecticut, New York, Maryland, and Minnesota for A phagocytophilum). Other clues include similar illness in family members or pets; recreational exposure; and exposure to brushy or grassy areas through hunting, hiking, fishing, camping, gardening, or other outdoor activities. The finding of ticks on other family members or pets is also concerning for potential exposure or illness. Patients may not recall tick exposure, but do recall a skin lesion associated with an unspecified insect bite, which could prompt further query about outdoor activities.
Other diseases to consider in the differential diagnosis include infection with Heartland or Bourbon virus, although both of those conditions are much milder or even subclinical. Francisella tularensis infection is also a consideration, especially pneumonic or typhoidal tularemia, because the clinical course can rapidly progress to severe septic shock. In this case, no single finding, including epidemiological clues, reliably distinguished between ehrlichiosis and tularemia. Lesions at the inoculation site (especially ulcerative lesions) and lymphadenopathy can suggest other forms of tularemia, although they may not be present in more systemic disease.
Laboratory findings seen in ehrlichiosis include many of the findings in the patient described in this case, including leukopenia with a left shift, thrombocytopenia, and anemia. Elevations in aminotransferase levels are common. In this patient, one concern was the possibility of hemophagocytic lymphohistiocytosis, given the multiple cytopenias, elevated triglyceride levels, and severely elevated ferritin. Ehrlichiosis has been associated with secondary hemophagocytic lymphohistiocytosis; given the fulminant course of this patient, this was clinically considered. On autopsy, focal hemophagocytosis was also noted, corroborating the diagnosis; however, the diagnostic criteria were only fulfilled postmortem.
Diagnosis of ehrlichiosis is difficult because of its nonspecific symptomatology and no clinically viable culture system. Diagnosis requires specific testing and a high index of suspicion to order appropriate testing. Identification of morulae on buffy coat examination can assist with the diagnosis; however, they are seen more frequently intracytoplasmic in neutrophils during infection with A phagocytophilum, and less frequently in mononuclear cells with E chaffeensis. Serological testing, either using an immunofluorescence antibody assay or enzyme-linked immunosorbent assay, is highly sensitive later in the course of disease (typically 7-14 days after onset), especially with testing of paired samples. Unfortunately, this reduces the clinical use, as treatment decisions are necessary well before that time. Also, serological testing is limited because of variability between laboratories in antigens, conjugates, and result interpretation. Nucleic acid detection also has similar limitations.
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Cite this: Zafar Jamkhana, Nirav Patel. Internal Medicine Case Challenge: A Highly Active 80-Year-Old Woman With Sudden Illness - Medscape - Apr 03, 2023.