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CNS Infections: An Indication for Continuous EEG Monitoring?
Abstract & Commentary
By Padmaja Kandula, MD, Assistant Professor of Neurology and Neuroscience, Comprehensive Epilepsy Center, Weill Medical College. Dr. Kandula reports no financial relationships relevant to this field of study.
Synopsis: In this retrospective study, the authors describe the prevalence and significance of both electrographic seizures and periodic discharges in critically ill patients with central nervous system infections.
Sources: Carrera E, Claassen J, Oddo M, et al. Continuous electroencephalographic monitoring in critically ill patients with central nervous system infections. Arch Neurol 2008;65: 1612-1618.
Acute symptomatic seizures are a known complication of central nervous system (CNS) infections. Traditionally, however, meningitides have been considered a medical and not neurological condition until focal neurologic signs or clinical seizures complicate the picture. In addition, use of continuous electroencephalography (cEEG) monitoring was not in wide practice until about a decade ago, when a landmark paper in 2000 by Towne and colleagues found an 8% incidence of nonconvulsive status epilepticus in a prospective study of patients with unexplained coma.1 Since then, physicians have noted that both electrographic seizures and nonconvulsive status epilepticus are under-recognized causes of coma. Interest in critically ill subpopulations such as those with CNS infections has grown. However, the true prevalence of electrographic seizures remains largely a mystery in this patient population. Hence, the authors of this study define and characterize the EEG findings in these critically ill patients.
Over a one-year time period, all patients with CNS infections who underwent cEEG were retrospectively identified. Inclusion criteria were a diagnosis of primary CNS infection and accompanying elevation of the cerebrospinal fluid (CSF) white blood cell count (>4 /microliter) with or without characteristic imaging abnormalities. Exclusion criteria included postoperative neurosurgical infections and noninfectious causes of CSF pleocytosis. Infections were further subdivided into viral, bacterial, and fungal/parasitic based on appropriate CSF findings, including positive polymerase chain reaction (PCR), culture, antigen detection, and lymphocytic (viral infections) or neutrophilic (bacterial infections) pleocytosis. Imaging characteristics were used to help classify the cases.
A total of 1,078 patients with a diagnosis of primary CNS infection were retrospectively identified at the Columbia University Medical Center. Seventy-five patients (7%) underwent cEEG, and 42 patients met full criteria for the study.
In the study group, 64% of infections were viral, 8% bacterial, and 7% either fungal or parasitic. Fourteen of 42 patients had confirmed electrographic seizures, and 11 of these patients had accompanying periodic epileptiform discharges (PEDs). PEDs were recorded in 40% of patients. Overall, nearly half (48%) of patients had either electrographic seizures or PEDs. PEDs and viral etiology were independently associated with electrographic seizures.
Clinical outcome was assessed in nearly all study patients (40 of 42 patients). Twenty-one patients had poor neurological outcome as assessed by a Glasgow outcome scale of 1-3. After adjustment for neurologic status, both PEDs and electrographic seizures were associated with poor outcome.
This paper, like other retrospective studies, suffer from the same inherent limitations. Selection bias (only patients in whom cEEG was requested were included in the study) and small numbers make it difficult to extrapolate these findings to other patients with CNS infection. From a practical and neurophysiologic standpoint, it is not surprising that periodic discharges are often forerunners to potential clinical or electrographic seizures. However, to date there have been no prospective long-term data that address the outcome of patients treated for both PEDs and electrographic seizures.
Currently, there is no consensus among neurologists or intensivists on if, when, and how to treat this subpopulation. For now, based on current retrospective evidence, cEEG should be considered in comatose patients with CNS infections, particularly viral infections, who fail to improve despite appropriate medical management. In our center, periodic discharges in high-risk patients, such as those with CNS infections, are treated with an anti-epileptic agent and continuously monitored for possible evolution of periodic discharges into electrographic seizures. Evolution of electroencephalographic activity then warrants additional treatment. A definitive prospective treatment trial of subclinical seizures and PEDs and long-term outcome is needed to determine appropriate treatment.
1. Towne AR, Waterhouse EJ, Boggs JG, et al. Prevalence of nonconvulsive status epilepticus in comatose patients. Neurology 2000;54:340-345.