neurologic disorders
Encephalitis
Diagnosis of Encephalitis
MRI Cerebrospinal fluid (CSF) testing Encephalitis is suspected in patients with unexplained alterations in mental status. Clinical presentation and differential diagnoses may suggest certain diagnostic tests, but MRI and CSF analysis (including polymerase chain reaction [PCR] for HSV and other viruses) are usually done, typically with other tests (eg, serologic tests) to identify the causative virus. Despite extensive testing, the cause of many cases of encephalitis remains unknown. Cytomegalovirus encephalitis should be considered in patients with HIV/AIDS or other immunocompromised conditions and can be diagnosed by PCR. Contrast-enhanced MRI is sensitive for early HSV encephalitis, showing edema in the orbitofrontal and temporal areas, which HSV typically infects. MRI shows demyelination in progressive multifocal leukoencephalopathy and may show basal ganglia and thalamic abnormalities in West Nile and eastern equine encephalitis. MRI can also exclude lesions that mimic viral encephalitis (eg, Brain Abscess , sagittal sinus thrombosis). CT is much less sensitive than MRI for HSV encephalitis but can help because it is rapidly available and can exclude disorders that make lumbar puncture risky (eg, mass lesions, hydrocephalus, cerebral edema). Lumbar Puncture (Spinal Tap) (spinal tap) is done. If encephalitis is present, CSF is characterized by lymphocytic pleocytosis, normal glucose, mildly elevated protein, and an absence of pathogens after Gram staining and culture (similar to CSF in aseptic meningitis). Pleocytosis may be polymorphonuclear in severe infections. CSF abnormalities may not develop until 8 to 24 hours after onset of symptoms. Hemorrhagic necrosis can introduce red blood cells (RBCs) into CSF and elevate protein. CSF glucose levels may be low when the cause is varicella-zoster virus, mumps, or lymphocytic choriomeningitis virus. CSF samples should be sent for viral identification using PCR or, in certain cases, detection of antiviral antibodies in CSF. PCR testing of CSF is the diagnostic test of choice for HSV-1, HSV-2, varicella-zoster virus, cytomegalovirus, enteroviruses, and JC virus. PCR for HSV in CSF is particularly sensitive and specific. However, results may not be available rapidly, and despite advances in technology, false-negative and false-positive results may still occur because of a variety of conditions; not all are technical failures (eg, the blood in a mildly traumatic CSF tap may inhibit the PCR amplification step). False-negative results can occur early in HSV-1 encephalitis; if a false-negative result is suspected based on clinical findings, testing should be repeated in 48 to 72 hours. A recently developed multiplex PCR process, which can detect multiple viral and other infectious agents simultaneously, provides diagnostic information within a few hours. Multiplex PCR results may need to be confirmed by conventional PCR. CSF viral cultures grow enteroviruses but not most other viruses. For this reason, CSF viral cultures have been superseded by PCR and are rarely used in diagnosis. CSF viral IgM titers are often useful for diagnosing acute infection, especially West Nile encephalitis, for which they are more reliable than PCR. CSF IgG and IgM titers may be more sensitive than PCR for encephalitis due to reactivated varicella-zoster virus infection. Paired acute and convalescent serologic tests of CSF and blood must be drawn several weeks apart; they can detect an increase in viral titers specific for certain viral infections. Brain biopsy may be indicated for patients who Are worsening Are responding poorly to treatment withacycloviror another antimicrobial Have a lesion that is still undiagnosed However, brain biopsy has a low yield unless it targets an abnormality seen on MRI or CT. 