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KEY POINTS

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  • Encephalomyelitis should be suspected in patients with neurologic findings including fever, headaches, odd behavior, altered sensorium, seizures, and focal neurologic deficits without obvious cause.

  • Course of symptoms, season of the year, travel, local outbreaks, occupation, animal or insect exposure, recent illness, immune status, age, and recent vaccine history all play a part in trying to establish a diagnosis. Physical examination is not usually revealing, but rashes, inoculation reactions, or pneumonia can be helpful clues.

  • An individualized workup based on the above includes culture, PCR, antigen detection, serologic IgM and IgG titers of noncentral nervous tissue, as well as cerebrospinal fluid (CSF) analysis if not contraindicated by examination. The results must be used carefully based on the context of the presentation.

  • CSF is almost always abnormal but a normal study does not preclude disease. A positive PCR or antigen study should help guide treatment. Cell counts in the CSF can be clues to nonviral causes (eg, eosinophilia with parasites and coccidioidomycosis).

  • Magnetic resonance imaging (MRI) is a key part of the workup and is more reliable than CT scan. Either of these tests should be obtained prior to lumbar puncture if possible.

  • Herpes simplex virus (HSV) is the most common cause of nonepidemic fatal encephalitis. Early treatment with acyclovir significantly reduces mortality.

  • Arboviruses are the most common cause of epidemic outbreaks worldwide and depending on the area and season may be a clue to the origin.

  • In all suspected cases of encephalomyelitis treatment with full-dose acyclovir should begin quickly until a diagnosis is established. A negative workup does not preclude HSV so empiric therapy is appropriate.

  • Supportive care, along with appropriate therapy, is essential because some patients recover even following protracted illness.

  • Consider bioterrorism in unexplained outbreaks, especially when the presentation is unusual or out of season.

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INTRODUCTION

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Encephalomyelitis is a combination of two disease states affecting the central nervous system (CNS). Encephalitis is defined as an inflammatory process of the brain associated with neurologic dysfunction; myelitis is an inflammatory process affecting the spinal cord. These may occur separately or together. Occasionally the covering of the brain is involved and therefore the term meningoencephalitis or meningoencephalomyelitis may be more appropriate.

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There are about 20,000 cases of encephalomyelitis reported per year. The approach to each suspected case of encephalomyelitis should be standard yet individualized based on that patient’s clinical presentation. The course of symptoms, season of the year, travel, local outbreaks, occupation, animal or insect exposure, recent illness, immune status, age, and recent vaccine history all play a part in establishing a diagnosis. Physical examination is not usually revealing, but rashes, inoculation reactions, or pneumonia can be helpful clues.

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Though viruses are the predominant cause of encephalomyelitis, autoimmune and acute disseminated encephalomyelitis (ADEM) may account for approximately 20% of cases. Other noninfectious causes of this syndrome must also be excluded, such as vasculitis, connective tissue diseases, and paraneoplastic syndromes.

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