MKSAP quiz on EEG


The following cases and commentary, which focus on the use of electroencephalography (EEG), are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 17).

Case 1: Status epilepticus

A 55-year-old man is treated in the emergency department for convulsive status epilepticus. He stops convulsing after receiving intravenous lorazepam and phenytoin but is still confused 30 minutes after treatment. According to his wife who accompanied him, a left temporal cavernous malformation was detected 3 years ago and has been managed conservatively. He has no significant family medical history and takes no chronic medication.

On physical examination, temperature is 36.8 °C (98.2 °F), blood pressure is 130/90 mm Hg, pulse rate is 115/min, and respiration rate is 12/min. The patient is generally stuporous but intermittently alert to voice or sternal rub. He occasionally utters nonsensical phrases, mostly consisting of syllables that are not real words, and inconsistently follows some one-step commands. Cranial nerves are intact, and pupils are symmetric and reactive. No weakness is detected in the face or limbs.

A CT of the head shows an acute hemorrhage in the region of the patient's cavernous malformation. The hemorrhage measures 0.5 × 0.5 × 1.0 cm. No significant mass effect or midline shift is noted.

Which of the following is the most appropriate next step in management?

A. Continuous electroencephalographic monitoring
B. Intravenous flumazenil
C. Urgent surgical resection of the vascular malformation
D. Withholding of further doses of antiepileptic drugs

View correct answer for Case 1

Case 2: Tonic-clonic seizure

A 32-year-old man is evaluated in the emergency department 2 hours after having a witnessed tonic-clonic seizure that lasted 2 minutes. After the seizure, he noted transient weakness of the right arm. The weakness has now resolved, and he feels completely normal. The patient reports that before losing consciousness, he felt a painful numbness in the first and second digits of the right hand, which subsequently assumed a “claw-like” posture. He never has had a similar sensation. He sustained a closed head injury resulting in a brief loss of consciousness 5 years ago in military combat. He takes no medication.

On physical examination, vital signs are normal. The patient's facial features are symmetric. Right pronator drift and difficulty with rapid alternating movements of the right hand are noted. Examination of the right upper extremity shows muscle strength of 4+/5 and 1+ deep tendon reflexes; muscle strength is 5/5 and reflexes are 2+ in all other limbs.

Laboratory studies, including a complete blood count, comprehensive metabolic profile, and urinalysis, have normal results.

An MRI shows encephalomalacia from his previous head trauma in the left parietal lobe and no other acute findings.

Which of the following is the most appropriate next step in management?

A. Ambulatory electroencephalographic monitoring
B. Carbamazepine
C. Clinical observation
D. Lumbar puncture

View correct answer for Case 2

Case 3: Aphasia and fever

A 65-year-old woman is hospitalized for fever and altered mental status. Four days ago, she experienced headaches and had a temperature of 39.0 °C (102.2 °F). Today she developed aphasia, prompting hospital admission. Her medical history is otherwise noncontributory, and she takes no medications.

On physical examination, temperature is 39.3 °C (102.7 °F), blood pressure is 122/64 mm Hg, pulse rate is 98/min, and respiration rate is 18/min. The patient is unresponsive and grimaces to sternal rub. The neck is resistant to passive flexion. All extremities move spontaneously. There is no rash.

Cerebrospinal fluid (CSF) studies show a leukocyte count of 150/µL (150 × 106/L) with 38% lymphocytes, 34% neutrophils, and 28% monocytes. The erythrocyte count is 0/µL (0 × 106/L), and glucose is 54 mg/dL (3.0 mmol/L). Protein is 137 mg/dL (1370 mg/L) and opening pressure is 150 mm H2O. A Gram stain shows no organisms and brain MRI shows no focal abnormality or hydrocephalus.

The patient is administered empiric therapy with dexamethasone, vancomycin, ceftriaxone, ampicillin, and acyclovir pending additional test results.

Which of the following is the most appropriate next step in management?

A. Monitor intracranial pressure
B. Perform transcranial Doppler ultrasonography
C. Perform electroencephalography
D. Start mannitol

View correct answer for Case 3

Case 4: Subarachnoid hemorrhage

A 57-year-old man is evaluated in the ICU 7 days after admission for a subarachnoid hemorrhage. An initial noncontrast head CT scan obtained in the emergency department showed a diffuse subarachnoid hemorrhage at the base of the brain that was thickest over the left hemisphere and accompanied by hydrocephalus. An external ventricular drain was placed to treat the hydrocephalus, and he subsequently underwent successful clipping of a 9-mm aneurysm of the left posterior communicating artery. Oral nimodipine was initiated.

On physical examination, temperature is 37.8 °C (100.1 °F), blood pressure is 138/78 mm Hg, pulse rate is 78/min, and respiration rate is 12/min. Neurologic examination shows an extremely somnolent patient who cannot follow commands and is unable to move the right arm and leg; on initial neurologic examination in the emergency department, the patient responded to loud noises, was able to follow simple commands, was oriented to time and place, and exhibited briskly reactive pupils and right arm drift.

Results of standard laboratory studies are normal.

Which of the following is the most appropriate next diagnostic test?

A. CT angiography of the brain
B. Electroencephalography
C. Lumbar puncture
D. MRI of the brain

View correct answer for Case 4

Case 5: History of seizures

A 40-year-old man is reevaluated for a 1-year history of recurrent tonic-clonic seizures that have not responded to treatment with valproic acid and topiramate. When describing the seizures, his wife says that he usually drops to the ground and begins “shaking all over”; the shaking typically lasts 10 to 15 minutes, with the patient's eyes remaining closed during the event. He subsequently is confused for 30 to 60 minutes. The seizures initially occurred 1 or 2 times per month but recently have been occurring every other day. On several occasions, he has become incontinent. He is a military veteran who sustained a closed head injury in combat 5 years ago and has posttraumatic stress disorder. Medications are twice daily valproic acid and topiramate.

On physical examination, vital signs are normal. General medical examination findings are normal. On neurologic examination, flattening of the nasolabial fold on the right is noted, and right pronator drift is present. Deep tendon reflexes are 3+ in the right upper and lower extremities. A plantar extensor response is noted in the right toe.

Results of laboratory studies are normal, with a serum valproic acid level within the therapeutic range.

An MRI of the brain reveals left frontal lobe encephalomalacia. An electroencephalogram (EEG) shows intermittent left frontal slowing.

Which of the following is the most appropriate management?

A. Ambulatory EEG monitoring
B. Carbamazepine
C. Levetiracetam
D. Video EEG monitoring

View correct answer for Case 5


Answers and commentary

Case 1

Correct answer: A. Continuous electroencephalographic monitoring.

This patient should have continuous monitoring with electroencephalography (EEG) because his presentation is concerning for nonconvulsive status epilepticus (NCSE). Approximately 48% of patients treated for convulsive status epilepticus (CSE) will continue to have subtle or subclinical seizures on EEG. Persistently altered mental status, particularly with waxing and waning features and focal neurologic deficits (such as aphasia), is a characteristic feature of NCSE. Patients with intracranial structural abnormalities who are comatose also are at high risk for this disorder. Intracerebral hemorrhage is an additional risk factor for nonconvulsive seizures and status epilepticus.

Continuous EEG monitoring is twice as sensitive as a routine 30-minute EEG for detecting seizures, especially the intermittent seizures that are common in patients already treated for CSE. All patients with altered mental status after CSE should have continuous EEG monitoring for at least 24 hours to detect nonconvulsive seizures or a changed status. Comatose patients should be evaluated for 24 to 48 hours. Continuous EEG monitoring is indicated in patients with acute structural intracranial lesions and altered mental status, even if clinically evident seizures have not occurred.

Flumazenil should not be administered to any patient with seizures or at risk for seizures because the drug can precipitate status epilepticus. Because the patient is not showing any signs of respiratory depression or other adverse effects of medication, there is no urgent need to reverse the benzodiazepine he received as part of appropriate CSE treatment.

Cavernous malformations usually have self-limited bleeding, and this patient does not have any mass effect or other urgent need for surgery. Although he ultimately may be a surgical candidate, given that refractory seizures are associated with cavernous malformations, surgical resection is not the most appropriate next step. He first should be evaluated and treated for NCSE.

Maintenance antiepileptic drugs (AEDs) should not be withheld in a patient with CSE at presentation unless the drugs are clearly causing severe adverse effects. In this patient, NCSE is a more likely explanation of the patient's mental state than is an adverse effect of the AED.

Key Point

  • All patients with altered mental status after convulsive status epilepticus should have continuous electroencephalographic monitoring for at least 24 hours to detect nonconvulsive seizures.

Return to the next case

Case 2

Correct answer: B. Carbamazepine.

This patient should receive an antiepileptic drug (AED), such as carbamazepine. His seizure was unprovoked. The 2-year risk of recurrence after a single unprovoked seizure is approximately 40%. On the basis on this estimate, most experts do not recommend starting an AED for a first seizure unless the patient has risk factors that increase the likelihood for future events. This patient, however, has several risk factors for future seizures, including previous head trauma with loss of consciousness, a focal brain lesion on MRI, and postictal Todd paralysis of the right arm (focal weakness after a seizure). His risk of future seizures is high, and he should be treated with an AED. In this patient, the brain injury involving the contralateral parietal lobe is likely the source of the seizure, with the abnormal sensation experienced at seizure onset representing a sensory aura. He most likely had a simple partial seizure starting in the parietal lobe that spread to the motor cortex, which led to the dystonic posture of his hand and subsequent tonic-clonic seizure.

Ambulatory electroencephalography (EEG) is an outpatient test that can be useful to exclude the presence of unrecognized seizures and provide a more sensitive evaluation of interictal discharges than a 30-minute EEG. This test, however, is not performed in the emergency department and does not have to be completed before starting treatment in this patient, who had a witnessed seizure and has a high risk of recurrent seizure.

Clinical observation is appropriate management of a single unprovoked seizure only in patients with no risk factors for future seizures.

A lumbar puncture is indicated in some patients with a first seizure if they have symptoms or signs of infection or have altered mental status. In this patient with a clear reason for a partial seizure, a normal mental status, and no signs of infection, a lumbar puncture is unnecessary.

Key Point

  • In a patient with a first seizure and risk factors for future seizures, treatment with an antiepileptic drug is appropriate.

Return to the next case

Case 3

Correct answer: C. Perform electroencephalography.

This patient has symptoms consistent with encephalitis (obtundation, fever, elevated cerebrospinal fluid [CSF] leukocyte count) and should undergo electroencephalography (EEG). Recent consensus guidelines promote standardized evaluation for encephalitis, which includes lumbar puncture, brain MRI, and EEG. EEG is indicated to confirm the diagnosis of encephalitis, provide information that may help identify a causative organism, and assess the need for antiepileptic therapy. Nonconvulsive seizures, defined as the presence of seizure activity on EEG in the absence of myoclonic movements or other clinical evidence of seizures, could contribute to alterations in consciousness. Nonconvulsive status epilepticus may be focal or generalized and has been reported with viral and autoimmune encephalitides. Nonconvulsive status epilepticus in patients with encephalitis is associated with a delay in initiating antiepileptic therapy and an increased risk for death.

Cerebral edema is a poor prognostic factor in encephalitis, and patients with evidence of increased intracranial pressure based on neuroimaging or increased opening pressure are best managed in an intensive care setting. The opening CSF pressure for this patient is within normal limits, indicating the absence of cerebral edema or increased intracranial swelling. Therefore, intracranial pressure monitoring or initiating mannitol, which is used to decrease intracranial edema, is not necessary.

Transcranial Doppler ultrasonography is useful for monitoring patients at risk for vasospasm after subarachnoid hemorrhage. It has not been found to be beneficial in the management of patients with encephalitis and would not be indicated in this patient.

Key Point

  • Standardized evaluation for encephalitis includes lumbar puncture, brain MRI, and electroencephalography.

Return to the next case

Case 4

Correct answer: A. CT angiography of the brain.

This patient should undergo CT angiography of the brain to assess for cerebral vasospasm. He is now at day 7 after a subarachnoid hemorrhage due to a left middle cerebral artery aneurysm. In the first 48 hours after a subarachnoid hemorrhage, rebleeding from an unsecured aneurysm and hydrocephalus are the principal causes of neurologic deterioration. This patient's aneurysm has been successfully clipped, and hydrocephalus is being managed with the use of an external ventricular drain. Potential neurologic complications after the first 48 hours include seizures, hydrocephalus, infection, and symptomatic cerebral vasospasm; the incidence of cerebral vasospasm peaks on days 5 to 10 after a hemorrhage. Cerebral vasospasm can manifest as a decline in neurologic function in patients who are awake enough for a neurologic examination. Although transcranial Doppler ultrasonography may reveal a vasospasm, CT angiography is more sensitive at detecting vasospasm that can be treated with the initiation of vasopressors to augment the blood pressure or with endovascular treatment in more refractory cases. CT angiography has the additional benefit of imaging the brain parenchyma for evidence of cerebral edema or infarction and the ventricles for evidence of hydrocephalus that may be amenable to shunting.

Electroencephalography (EEG) is inappropriate as the next diagnostic step in this patient with an aneurysmal subarachnoid hemorrhage. Convulsive and nonconvulsive status epilepticus is common and underdiagnosed after hemorrhagic stroke and is associated with poor neurologic outcome. If imaging does not identify a clear cause of the patient's decline that can be treated with medical or surgical therapy before irreversible damage occurs, then continuous EEG monitoring may help in diagnosing seizures.

Lumbar puncture may be useful for measuring intracranial pressure in this patient with an external ventricular drain. However, repeat imaging would first be required, independent of the presence of the drain, to rule out mass effect that could precipitate cerebral herniation after a lumbar puncture.

MRI requires too long a time to complete in the setting of a neurologic emergency and may not adequately detect arterial narrowing. Vasospasm is more readily detected with CT angiography.

Key Point

  • Cerebral vasospasm is a potential complication of subarachnoid hemorrhage that most often occurs 5 to 10 days after the hemorrhage and is best detected by CT angiography of the brain.

Return to the next case

Case 5

Correct answer: D. Video EEG monitoring.

This patient should have continuous video electroencephalographic (EEG) monitoring for further evaluation of the seizures, which have become increasingly frequent and have not responded to two antiepileptic drugs (AEDs). Video EEG monitoring, performed in an epilepsy-monitoring unit, enables correlation of patient behavior with seizure activity on an electroencephalogram. This can lead to better characterization of seizure activity, such as the identification of specific localizing features, and allow assessment of potential non–seizure-related behaviors suggestive of nonepileptic seizures. This patient has several risk factors for psychogenic nonepileptic events. The long duration of the episodes is more typical of nonepileptic than epileptic seizures, as is the fact that his eyes remain closed during the event. The presence of incontinence does not exclude a nonepileptic episode. Although his previous closed head injury puts him at risk for epileptic seizures, it does not exclude the possibility of nonepileptic events. In fact, combat veterans, particularly those with posttraumatic stress disorder (PTSD), are at high risk for nonepileptic seizures. This diagnosis can be overlooked if a history of head trauma is present. Because epileptic and nonepileptic seizures can coexist in the same patient, a thorough description and characterization of the seizures are essential and best achieved by admission to an epilepsy monitoring unit.

Ambulatory EEG monitoring allows more prolonged evaluation of brain activity outside a clinical setting and may be helpful in identifying seizures or interictal epileptiform activity that may not have been seen on a routine interictal EEG study. However, inpatient video EEG monitoring allows analysis of both clinical and EEG characteristics of seizures to assist in diagnosis and management. The latter study is required for a diagnosis of nonepileptic seizures and presurgical evaluations in patients who have not responded to two or more AEDs. The inpatient setting also allows for withdrawal of AEDs in a monitored environment.

A definitive diagnosis is necessary before adding more AEDs, such as carbamazepine or levetiracetam. Furthermore, levetiracetam should be avoided in this patient with PTSD because it can exacerbate anxiety and irritability.

Key Point

  • Video electroencephalography, performed in an epilepsy-monitoring unit, enables correlation of the patient's behavior with seizure activity on an electroencephalogram, which can lead to better characterization of seizure activity or allow assessment of potential non–seizure-related behaviors suggestive of nonepileptic seizures.