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545 - Rocky Mountain Spotted Fever with Acquired HLH and Chronic Encephalopathy After Delayed Diagnosis in a Low-Risk Region: A Case Report

Thursday, February 27, 2025

5:00 PM - 6:30 PM MST

Co-Author(s)

NE

Norberto Escobales, MD

Resident Physician
Temple University Hospital
Philadelphia, Pennsylvania, United States
AS

Abhishek Shrinet, MD

Resident Physician
Temple University Hospital
Philadelphia, Pennsylvania, United States
LG

Luis A. Guinand, MD

Pgy-3 Resident
Temple University PM&R
Philadelphia, Pennsylvania, United States

Presenting Author(s)

AJ

Alex Jiang, BA

Medical Student
California Northstate University, College of Medicine
Green Brook, New Jersey, United States

Case Diagnosis: Chronic encephalopathy secondary to acquired hemophagocytic lymphohistiocytosis (HLH) associated with Rocky Mountain Spotted Fever (RMSF).

Case Description: A 65-year-old presented with fluctuating mental status and cognitive decline over two weeks after a fishing trip to New Jersey. Initially evaluated at multiple urgent care centers, he was discharged due to transient symptom improvement and unremarkable workups. On admission, he was febrile, altered, and unresponsive to empiric antibiotics. A broad infectious workup was negative, but he developed a pink maculopapular rash, polyarthralgias, and diffuse hyperintense signal abnormalities on brain MRI. Suspecting adult-onset Still’s disease with macrophage activation syndrome, glucocorticoid therapy was initiated with only mild improvement. Subsequent testing identified Rickettsia rickettsii and RMSF, aligning with his travel history despite no observed tick bite. Doxycycline was then initiated; however, his cognitive baseline progressed to chronic encephalopathy, secondary to HLH with central nervous system involvement. His inflammatory markers improved, yet his mental status remained impaired despite further treatment with anakinra and glucocorticoids.

Discussions: RMSF, caused by Rickettsia rickettsii, is exceptionally rare in the northeastern United States. In New Jersey, a 2020 tick screening found no R. rickettsii-infected ticks, though recent studies indicate an expansion of the American dog tick, the primary vector of RMSF, further into the Northeast, potentially raising infection risk.Though classic symptoms are recognized, confirmation by serology may take 7-10 days. Early treatment with doxycycline is essential as prognosis improves significantly with prompt therapy; in fact, 88.4% of HLH cases associated with tick-borne diseases respond to antibiotic therapy alone. In this case, doxycycline was delayed to one week after hospital admission and three weeks after symptom onset.

Conclusions: Increased provider education on early RMSF recognition and timely doxycycline initiation is vital to reduce RMSF-related mortality and complications, such as chronic encephalopathy. Enhanced tick surveillance may also help identify emerging endemic areas for this traditionally regional infection.