DISORDERS THAT PRESENT WITH ENCEPHALOPATHY (SEE ALSO CHAPTER 17 COMA ) Goals of Treatment Encephalopathy is an imprecise term that implies diffuse brain dysfunction with or without alterations in the level of consciousness Encephalopathy may be a sign of numerous systemic disorders, or it may result from primary disorders of the CNS, the most common of which is encephalitis The emergency physician must decide whether the child’s degree of irritability, uncooperativeness, and lethargy is proportionate to the degree of systemic illness; whether it is caused by fear; or whether it represents cortical dysfunction Encephalopathy has a large differential and can be associated with cardiorespiratory compromise, requiring prompt identification and a systematic approach to evaluation CLINICAL PEARLS AND PITFALLS A detailed clinical history is imperative to identifying a likely etiology Herpes simplex virus (HSV) polymerase chain reaction testing of CSF samples is recommended for all children with suspected encephalitis Empiric therapy with IV acyclovir is recommended for all patients with suspected encephalitis while confirmatory tests are pending MRI with diffusion-weighted imaging is the imaging modality of choice for the evaluation of encephalitis Encephalitis Encephalitis is an inflammation of the brain parenchyma Meningoencephalitis refers to additional leptomeningeal involvement, whereas encephalomyelitis implies involvement of the spinal cord CNS dysfunction can be caused by direct invasion of the brain by a pathogen; immunologic mechanisms as in postinfectious encephalomyelitis, or be mediated by a toxic-metabolite, such as drugs and toxins Viral encephalitides are caused by a wide variety of viruses that lead to clinically similar illnesses ( Table 97.7 ) An etiology is often not identified, but when one is, enterovirus is the most commonly identified cause Prior to introduction of the vaccine, mumps had been the most common cause of meningoencephalitis, with up to 50% of patients with mumps parotitis having