A challenging case of encephalopathy in an endemic region of Texas with normal neuroimaging: A case report

Introduction: Murine typhus is a zoonotic disease caused by Rickettsia typhi, an obligate intracellular, gram-negative bacteria; in the past rats and their fleas have been the main reservoirs and vectors, but currently more cases are linked to cats, opossums, and cat fleas. The bacteria cause infection of the vascular endothelial cells, resulting in vasculitis, increased vascular permeability and fluid leakage, which may lead to pulmonary and cerebral edema. When immune cells in the visceral organs are infected, acute kidney injury, hepatitis, and encephalitis can occur. Neurological symptoms, particularly encephalitis, are uncommon. Blood tests generally reveal metabolic abnormalities including hypoalbuminemia, hypokalemia, raised inflammatory markers, elevated liver enzymes, and thrombocytopenia. A confirmatory diagnosis can be made by detecting high antibody titers together with a fourfold rise on repeat testing. The cerebrospinal fluid (CSF) usually has pleocytosis with the lymphocytes being the dominant cell type. Neuroimaging may vary from being normal to showing cerebral edema or infarction due to vasculitis. Case Report: A 78-year-old woman was brought from another hospital because she had symptoms of generalized weakness and a change in mental state. Her initial laboratory tests indicated low potassium levels, low albumin levels, raised liver enzymes, and increased inflammatory markers. A chest computed tomography (CT) scan showed multifocal pneumonia. She was first given a broad-spectrum antibiotic treatment for the pneumonia; but since her encephalopathy did not improve, a consultation was arranged to consider the possibility of encephalitis. The results of the lumbar puncture were found to be consistent with a traumatic tap, and the cerebrospinal fluid analysis, together with the encephalitis panel, was otherwise normal. The neuroimaging did not show any acute abnormalities. Further information was obtained which showed that she had significant contact with cats, leading to a suspicion of murine typhus. The antibiotic treatment was changed to doxycycline. Serological tests confirmed the diagnosis, the antibody titer being 1:512. Her mental condition improved considerably as a result of doxycycline alone. Conclusion: Murine typhus encephalitis should be considered as part of the differential diagnosis in cases of patients who have altered mental status and metabolic imbalances, especially in instances where both the cerebrospinal fluid and neuroimaging are normal, particularly in areas where the disease is endemic such as Texas. By taking a thorough history of the patient’s exposure and geographical background, including any contact with cats, it is possible to facilitate a timely diagnosis and suitable treatment. Clinical outcomes are better when the condition is detected and treated early.