Case Presentation: Anaplasma phagocytophilum, a gram-negative tick-borne pathogen, presents with a notably diverse clinical spectrum ranging from mild flu-like symptoms to multi-organ failure. A 50-year-old man initially presented after experiencing two syncopal episodes. His course began with malaise and weakness, followed by a day of profuse diarrhea and subsequent syncope without any prior history of syncope or seizure-like activity. On arrival, he was febrile to 103°F and started on ceftriaxone and metronidazole for presumed colitis. He remained well appearing but continued to have high fevers and watery diarrhea. Laboratory evaluation showed pancytopenia and markedly elevated inflammatory markers, including a ferritin peak of 20,000 ng/mL, elevated LDH, and elevated ESR and CRP. Infectious, autoimmune, and malignant workups were negative. HLH was considered but later ruled out. The combination of persistent fever, gastrointestinal symptoms, cytopenias, and marked hyperferritinemia raised concern for a significant yet unidentified process. On review of his history, he reported a recent hike with his children, which prompted testing for tick-borne disease despite the absence of rash. PCR returned positive for Anaplasma phagocytophilum, and he improved with doxycycline.
Discussion: Clinically, anaplasmosis often presents as an acute febrile illness with myalgias, headache, and gastrointestinal symptoms. Up to one third of patients do not recall a tick bite or clear exposure history (Schudel et al). Laboratory abnormalities commonly include leukopenia, thrombocytopenia, and elevated transaminases, while severe disease may demonstrate a marked inflammatory response, including hyperferritinemia (Uminski et al; Katragadda et al). Morbidity includes progression to organ failure, ICU admission, and in untreated cases, mortality rates of 1 to 3 percent (Schudel et al). These nonspecific symptoms and seasonal clustering contribute to delays in recognition and highlight the need to consider tick-borne illness early in compatible cases. In one hospital system, 55 percent of anaplasmosis cases had delayed diagnostic testing, which was associated with worse outcomes (Pancholi et al). Cognitive biases such as anchoring, confirmation, and overconfidence may further contribute to delayed recognition (Kunitomo et al). Clinicians must revisit the differential and re-interview the patient when diagnostic uncertainty persists.
Conclusions: A brief follow-up discussion regarding outdoor exposure prevented a potentially dangerous delay in care for this patient. This case emphasizes the importance of recognizing the variable presentations of anaplasmosis and maintaining suspicion for tick-borne disease in patients with unexplained fever, cytopenias, and markedly elevated inflammatory markers.