AAN guideline reassesses the use of neuroimaging in the evaluation of seizure

American Family Physician,  April 1, 2008  by Amber Huntzinger

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Guideline source: Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology

Literature search described? Yes

Evidence rating system used? Yes

Published source: Neurology, October 30, 2007

Available at: http://www.neurology.org/cgi/content/full/69/18/1772

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The Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology (AAN) has reassessed the use of neuroimaging in patients presenting to the emergency department with seizure. Recommendations are based on 15 studies evaluated by physicians with expertise in neurology, epilepsy, neuro-radiology, neurosurgery, or emergency medicine. The guideline focuses on two parameters: the effectiveness of neuroimaging as a screening tool to analyze the need for a change in acute treatment and the clinical and historical features that suggest the need for neuroimaging.

Neuroimaging to Change Acute Treatment

Change in clinical treatment is defined as the discovery of a new structural lesion or the need for surgery based on an abnormal computed tomography (CT) finding. The guideline includes the following recommendations based on the likelihood that neuroimaging will lead to treatment changes in different groups of patients (Table 1).

ADULTS WITH FIRST SEIZURE

An emergency CT may be considered in adults with first seizure.

Five studies including 98 to 875 patients with non-febrile seizure showed that, overall, CT scans in the emergency department are possibly useful in this population. In these studies, 34 to 56 percent of patients had an abnormal CT finding, including brain atrophy. Common abnormalities that led to a change in treatment included traumatic brain injury, subdural hematoma, nontraumatic bleeding, cerebrovascular accident, tumor, and brain abscess.

CHILDREN WITH FIRST SEIZURE

An emergency CT may be considered in children with first seizure.

Four studies including 25 to 475 patients with seizure (not excluding complex febrile seizures) showed that, overall, CT scans are possibly useful in this population. In these studies, 0 to 21 percent of patients had an abnormal CT finding. Common abnormalities that led to a change in treatment included cerebral hemorrhage, tumor, cysticercosis, and obstructive hydrocephalus.

PATIENTS WITH CHRONIC SEIZURE

There is no recommendation for the use of an emergency CT in patients with chronic seizure.

Evidence is lacking on the likelihood of neuroimaging changing treatment in patients with chronic seizure. However, three studies, including 60 to 139 patients with chronic seizure and 24 to 138 patients with first seizure, showed no difference between the two groups in the number of abnormal CT findings. Overall, 12 to 25 percent of patients had an abnormal CT finding. Common abnormalities included cerebral hemorrhage and shunt malfunction.

SPECIAL POPULATIONS

An emergency CT may be considered in children younger than six months and in patients with acquired immunodeficiency syndrome (AIDS).

Three studies included a special population (i.e., age younger than six months, immediate posttraumatic seizure, or AIDS). Children younger than six months with seizure and patients with AIDS and first seizure had high rates of abnormalities on CT; therefore, CT scans are possibly useful in these populations. Children with immediate posttraumatic seizure had a low rate of CT abnormalities leading to a change in treatment. Common abnormalities in children younger than six months included Aicardi's syndrome, Miller-Dieker syndrome, tuberous sclerosis, infarction, and depressed skull fracture. Central nervous system toxoplasmosis was common in patients with AIDS.

Features Suggesting the Need for Neuroimaging

An emergency CT should be considered in patients presenting to the emergency department with seizure who have an abnormal neurologic examination, a predisposing history, or focal onset of seizure.

The evaluation of features associated with abnormal CT findings focused on any abnormality, not just those that led to a change in treatment. An analysis of nine studies identified several features associated with neuroimaging (Table 2). Multiple studies showed that a focal abnormality on neurologic examination, a predisposing history, or focal onset of seizure is associated with abnormal findings.

Future Research

The evidence does not support strong recommendations because many of the studies analyzed did not mask the clinical presentation and included varying patient populations. None of the studies included good data on the use of magnetic resonance imaging (MRI); therefore, no recommendations could be made. Future research should address the emergent use of MRI in patients presenting to the emergency department with seizure because MRI may be more sensitive than CT for detecting brain pathology underlying seizure disorders.

Table 1. likelihood of CT leading to a Change
in Acute Treatment of patients presenting to
the emergency department with seizure

                                           Number of CT
                                           scans that changed
                                           treatment/total number
Patients                                   of CT scans (%)

Adults with nonfebrile first seizure       272/1,566 (17)
Children with first seizure *               47/673 (7)
Special populations
  Children younger than six                 12/22 (55)
    months with seizure
  Patients with AIDS and first seizure       7/26 (27)

NOTE: Evidence is lacking on the likelihood of neuroimaging
changing treatment in patients with chronic seizures. Children
with immediate posttraumatic seizure had a low rate of CT
abnormalities leading to a change in treatment.

CT = computed tomography; AIDS = acquired immunodeficiency
syndrome.

*--Not excluding complex febrile seizures.

Table 2. Factors Associated with Abnormal
CT findings in Patients Presenting to the
Emergency Department with Seizure

Focal abnormality on neurologic examination
Predisposing condition *
Focal onset of seizure
Absence of a history of alcohol abuse
History of cysticercosis
Altered mentation
Patient older than 65 years
Seizure duration of more than 15 minutes

CT = computed tomography.

*--Age younger than six months, closed head injury, recent
cerebrospinal fluid shunt revision, malignancy, neurocutaneous