Emergency and Continuous EEG at University Hospital:
Essential Tests to Identify Non-Convulsive Seizures In Critically Ill Patients
By Michael Privitera, MD
Professor of Neurology
Director, Epilepsy Center, UC Gardner Neuroscience Institute
University Hospital is the only hospital in the Greater Cincinnati region to offer round-the-clock availability of emergency EEG for patients in the hospital or in the Emergency Department. Using this critical procedure, we can identify patients who present with alteration in consciousness, ranging from mild confusion to coma, where the underlying cause is ongoing seizure activity. In most of these patients the EEG is the only way to detect these subtle seizures; even a skilled clinician can be fooled. Here is an example of the kind of cases we have identified and treated over the past several decades:
A 37-year-old man was involved in a motor vehicle crash and experienced multiple traumatic injuries with extremity fractures and a loss of consciousness. The MRI scan showed a 1.5 cm intracerebral hemorrhage in the right frontal region. The patient was sedated and intubated. The treating team felt the patient was not responding to commands appropriately and called a neurology consult. The neurology team felt the lack of responsiveness was out of proportion to the brain injury and sedation and ordered an emergency EEG. The on-call EEG technologist was paged on Saturday afternoon, rushed to the hospital, and within an hour the EEG was being recorded. The neurology team saw rhythmic spike discharges on the EEG. They called the on-call EEG specialist who viewed the EEG from her home computer via remote access and verified that the EEG showed non-convulsive status epilepticus, with recurrent seizures arising from the right frontal region. Antiepileptic treatment was instituted within minutes of starting the EEG, and the patient rapidly showed improved responsiveness and began following commands. The patient remained hooked up on EEG for the next three days to ensure adequate treatment of seizures.
In the case presented, the only clinical sign of non-convulsive status epilepticus was lack of responsiveness—not the typical tonic-clonic movements or twitching one might expect. In this case, like many others, the only way to make the diagnosis was the EEG. The Epilepsy Center team has performed thousands of emergency and continuous EEG procedures over the past 20 years and is a leading center for research in this important field. (The image below shows an EEG, with continuous spiking and suppression periods, of an unresponsive patient.)
Here are answers to frequently asked questions about non-convulsive status epilepticus and emergency EEG.
Question: What is the difference between convulsive and non-convulsive seizures and status epilepticus?
Answer: Status epilepticus is defined as a state of continuous seizure activity, or recurrent seizure activity without return to normal consciousness, lasting 30 minutes or more. Most healthcare professionals are familiar with convulsive or tonic-clonic status epilepticus, a condition in which the patient experiences continuous convulsive movements.
Convulsive status epilepticus is dangerous; there is substantial mortality, and we know from animal studies that when the brain continues to be in a seizure state for more than 30 minutes, neurons start to die. Clinicians follow a rigorous protocol with high doses of antiepileptic drugs administered quickly in order to stop the seizure activity as soon as possible.
Other seizure types like complex partial may also evolve into status epilepticus, but complex partial status epilepticus can be much more difficult to recognize. The typical isolated complex partial seizure involves a confusional state, sometimes lip smacking or chewing movements, a blank stare, and occasionally abnormal posturing of the arms.
Complex partial seizures typically last 60 to 90 seconds and are followed by a few minutes of confusion or language disturbance. When complex partial seizures evolve into status epilepticus, the clinical manifestations become more difficult to recognize. Patients may present with confusion that can look like anything from a stroke to intoxication.
Rarely, patients may even appear to be hallucinating, and complex partial status epilepticus may be misdiagnosed as psychosis. In the hospitalized patient, especially when there are other causes of depressed consciousness, complex partial status, or “subtle status epilepticus” as it is also called, may manifest as coma or lack of responsiveness as in the case above.
Often one may see subtle twitching movements of the body or repetitive abnormal eye movements in an unresponsive patient as a clue that unrecognized seizure activity is present. However, in the study our group published in 1994, in which we identified 74 patients with non-convulsive status over a two-year period at University Hospital, about one-third had altered awareness as their only clinical manifestation of status.
The most common clinical presentations of non-convulsive status epilepticus are:
- Altered consciousness that is unexplained
- Persistent altered consciousness following a tonic-clonic seizure
- Altered consciousness with subtle motor twitching or eye blinking
Question: How common is non-convulsive status epilepticus in the hospital?
Answer: Non-convulsive status epilepticus was thought to be a rare phenomenon before the 1980s. In our article from 1994 we found 74 cases over a two-year period at University Hospital. Following this, large studies of status epilepticus including several multi-center studies have shown that non-convulsive status epilepticus may be present in 10 to 30 percent of hospitalized patients with otherwise unexplained altered mental status. It is important to remember how common this problem can be because if clinicians don’t think about it and don’t order the EEG, the diagnosis will not be made.
Question: Which patients are at highest risk for non-convulsive status epilepticus?
Answer: Patients with the following disorders appear to be at highest risk:
- Traumatic brain injury
- Subarachnoid hemorrhage
- Cardiopulmonary arrest
- A history of seizures
- Patients who have experienced one or more typical seizures, but are not returning to normal within 15 to 30 minutes.
- Brain tumors
- Induced hypothermia
- Any patient with unexplained depression of consciousness
Question: Is non-convulsive status epilepticus as dangerous as convulsive?
Answer: No one knows the exact answer to this question. However, we do know that convulsive status epilepticus is associated with substantial mortality and death of neurons if it is inadequately treated. We’re not sure that non-convulsive status is as harmful as convulsive status, but we do know that continuous seizure activity is dangerous to the brain. Therefore, most neurologists and epilepsy specialists treat non-convulsive status as an emergency and try to stop seizures as quickly as possible.
Question: How is non-convulsive status epilepticus treated?
Answer: We start treatment with intravenous antiepileptic drugs and benzodiazepines like lorazepam or midazolam. The standard protocol combines a benzodiazepine with the drug phenytoin, but many neurologists and epilepsy specialists are now using intravenous levetiracetam because of its ease of use, lack of drug-drug interactions, and overall safety profile. Members of the Epilepsy Center, under the leadership of Jerzy Szaflarski, MD, PhD, and Lori Shutter, MD, recently completed a study showing that levetiracetam was safer and better tolerated than phenytoin in an ICU population.
If these treatments fail to stop seizures, the next level of treatment involves using pentobarbital, phenobarbital or propofol, medications that carry more risk of adverse effects. In many cases of non-convulsive status the risks of treatment must be balanced against the risks of ongoing seizure activity. Many of these patients have multiple medical problems – they are almost always intubated — and the use of powerful anesthetic agents like pentobarbital or propofol may produce unwanted respiratory and cardiac side effects. Care of patients with non-convulsive status epilepticus usually requires a team of neurologists and neurointensivists; this is how we provide treatment at the UC Gardner Neuroscience Institute.
Question: If I see a patient who I think might have non-convulsive seizures, how do I request an urgent EEG? And who interprets the EEG?
Answer: Emergency EEGs are ordered through the EEG/EMU department of University Hospital (584-4408). Neurologists, neurosurgeons and neuroscience ICU physicians can order an emergency EEG; other services need to notify the Neurology consult team. If the EEG technologist is not in the hospital, the University Hospital operators will page the on-call technologist. The EEG will be reviewed first by the neurologist or NSICU physician ordering the test. An Epilepsy Center faculty member is always on call and will have remote access to the EEG.
The Epilepsy Center of the UC Gardner Neuroscience Institute has earned recognition as a Level 4 (highest level) epilepsy center for 21 consecutive years. We provide world-class diagnosis and treatment of epilepsy and are a major center for epilepsy surgery. Our research programs are recognized worldwide. Our EEG technologists, working closely with our Neurocritical Care team, provide round-the-clock availability of emergency EEG for rapid identification and to guide treatment of convulsive and non-convulsive status epilepticus, life-threatening conditions that are under-recognized in hospitalized patients.