Cases

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Cases

Case 13.1 Cardiac Arrest With Posthypoxic Myoclonus

Ervin L. Johnson III

HIGHLIGHTS

• EEG features carry valuable prognostic information in the aftermath of a cardiopulmonary arrest

• Myoclonic status epilepticus (MSE) with a burst-suppression pattern within the first 24 hours after anoxic injury is associated with a poor outcome

INTRODUCTION

Clinical History

A previously healthy 15-year-old male had sudden loss of consciousness while playing basketball with his friends. Emergency medical services found him pulseless and apneic. There was return of spontaneous circulation after 15 minutes of cardiopulmonary resuscitation (CPR). The patient was intubated in the field and brought to a nearby children’s hospital for further management.

Physical Examination

Initial neurologic examination (in the absence of sedation and neuromuscular blockade) showed no response to noxious stimulation, sluggishly reactive pupils, and absent corneal reflexes.

GUIDE TO INITIAL CASE DISCUSSION

Basic Concepts

Describe this patient’s initial level of consciousness and quantify his initial examination findings using the Glasgow Coma Scale.

What is the differential diagnosis for this patient’s comatose state?

What is your next step in the diagnosis and management of this patient?

Describe This Patient’S Initial Level of Consciousness and Quantify His Initial Examination Findings Using the Glasgow Coma Scale

On initial examination, this patient was comatose with a Glasgow Coma Scale score of 3T, with 1 point for eye opening (none), 1 point for verbal response (none), and 1 point for motor response (none), with the “T” indicating the presence of an endotracheal tube. Table 13.1.1 summarizes the Glasgow Coma Scale and Pediatric Glasgow Coma Scale.

What is the Differential Diagnosis for This Patient’S Comatose State?

This patient’s presumed period of absent cerebral blood flow prior to the initiation of CPR raises concern for anoxic brain injury. The differential for his sudden loss of consciousness is broad. Consideration should be given to a primary cardiac arrest due to a cardiomyopathy, arrhythmia, or structural abnormality. Possible central etiologies include subarachnoid hemorrhage due to a ruptured cerebral aneurysm or intraparenchymal hemorrhage secondary to a ruptured arteriovenous malformation. A large territory arterial ischemic stroke due to a dissection or other thromboembolic event is also possible. A primary respiratory arrest is also on the differential, although is less likely given the absence of preceding symptoms. In addition, a toxic ingestion must also be considered.

What Is Your Next Step in the Diagnosis and Management of This Patient?

Neuroprotective measures should be initiated. A CT scan should be performed to assess for signs of cerebral injury, both ischemic and hemorrhagic, with the caveat that CT has poor sensitivity for ischemic injury in the first few hours after the event. If there is evidence of intracranial hemorrhage, especially intraparenchymal, intraventricular, or subarachnoid, CT angiography may be warranted. Given the sudden loss of consciousness of unknown etiology, a cardiac evaluation with echocardiogram and telemetry is also warranted. This patient is at high risk for nonconvulsive seizures in the aftermath of his cardiac arrest. As such, continuous EEG monitoring should be initiated.² This is also useful for prognostication and for assessing overall cerebral function.

CLINICAL COURSE

Head CT scan showed signs of cerebral edema, including diffuse sulcal effacement and loss of grey–white differentiation. Toxicology screen was negative. Neuroprotective measures and continuous EEG monitoring were initiated.

ADVANCED TOPICS

Describe the EEG findings shown in Figure 13.1.1.

How do the EEG findings in this patient inform your understanding of his presentation?

Describe the EEG Findings Shown in Figure 13.1.1

Six hours after his arrest, EEG showed a burst suppression pattern with bursts that were time-locked with myoclonic movements consisting of eye opening and neck/trunk extension consistent with MSE (Figure 13.1.1).

How Do The EEG Findings in This Patient Inform Your Understanding of His Presentation?

In addition to monitoring for seizures and status epilepticus, EEG plays an important role in informing the prognosis of cardiopulmonary arrest survivors who develop posthypoxic myoclonus, as in this case.^3–7 Posthypoxic myoclonus—repetitive myoclonic movements of the face, extremities, and/or trunk—has long been considered an ominous clinical sign.^3–5 More specifically, patients exhibiting MSE with a corresponding burst-suppression pattern on EEG within the first 24 hours of injury have a high likelihood of a poor outcome.⁵ As such, the presence of MSE with an accompanying burst-suppression pattern on EEG portends a very poor prognosis in this patient. Of note, there are rare exceptions to the association of posthypoxic myoclonus with a poor outcome, and this is discussed in further detail below.^8,9

CLINICAL COURSE CONTINUED

Over the first 48 hours after admission, the patient’s myoclonus abated, his EEG transitioned to background suppression, and he lost all brainstem reflexes. A repeat head CT showed worsened cerebral edema and downward transtentorial and transforaminal herniation. His parents chose to discontinue technical support.

**FIGURE 13.1.1.** **Posthypoxic myoclonus.** Bipolar montage. This EEG shows a burst-suppression pattern with bursts of high amplitude (note scale bar) mixed frequency activity with embedded spikes and polyspikes; these were time-locked to myoclonic movements of the eyes, neck, and trunk. Settings: LFF 1 Hz, HFF 70 Hz.

484ADVANCED TOPICS CONTINUED

Discuss the indications for EEG monitoring after cardiopulmonary arrest.

How does the identification of postanoxic myoclonus affect neurologic prognosis?

Describe EEG features that provide prognostic information after cardiopulmonary arrest.

Discuss the Indications for EEG Monitoring After Cardiopulmonary Arrest

Numerous studies have attempted to identify predictors of outcome in cardiac arrest survivors.^5,10,11 Because neurologic prognosis often drives goals-of-care discussions, the ability to accurately predict neurologic outcome is critical. To prevent a negative prognosis from leading to premature or unnecessary cessation of life-sustaining therapies, most studies have been designed to identify survivors who are likely to have a poor neurologic outcome.^5,10 Accurate assessments in the pediatric population are arguably more crucial, as inaccurately predicting a poor outcome or falsely predicting a good outcome has consequences over a longer time frame.^12,13 While EEG is considered an adjunct to the clinical assessment, it is among the most reliable tools available for predicting outcome after cardiac arrest.^14–16

The American Clinical Neurophysiology Society’s consensus statement on continuous EEG in critically ill adults and children outlines indications for EEG monitoring in this population.² Among the cited indications, the most salient to the present discussion are “diagnosing seizures and other paroxysmal events” and “assessing encephalopathy severity and prognostication.” EEG may identify subclinical seizures in 10% to 47% of pediatric cardiopulmonary arrest survivors.^17–20 The impact of seizures on neurologic outcome in the setting of pediatric cardiac arrest remains unclear, although a large study of a heterogeneous pediatric population showed that a higher seizure burden is associated with worse outcome.²¹

How Does the Identification of Postanoxic Myoclonus Affect Neurologic Prognosis?

As detailed earlier, EEG also plays an important role in assessing cardiopulmonary arrest survivors who develop posthypoxic myoclonus. As noted earlier, MSE is associated with a poor prognosis. In contrast, EEG showing a continuous background with epileptiform activity that is predominant at the vertex and time-locked with myoclonus is associated with a fair outcome.^6,7,9 Another form of posthypoxic myoclonus, Lance-Adams Syndrome (LAS), is associated with a good neurologic prognosis.^8,9,22 LAS is a movement disorder that typically occurs once a patient has regained consciousness, is marked by intention and stimulus-induced myoclonus, and is thought to be due to death of Purkinje cells in the fastigial nucleus of the cerebellum.^9,23,24 In addition to clinical features, such as later myoclonus onset and predominant involvement of distal rather than proximal muscle groups, the myoclonic jerks seen in LAS are not associated with a change on EEG.

Describe EEG Features That Provide Prognostic Information After Cardiopulmonary Arrest

EEG background features carry valuable prognostic information in the aftermath of a cardiopulmonary arrest. These features can be considered “benign” or “malignant” with a subset of “highly-malignant” features being most closely correlated with a poor outcome.^{10,11,25–27} Westhall and colleagues reviewed 103 adult cardiopulmonary arrest survivors and showed that neurologic outcome was poor in all patients with one highly malignant EEG feature and in 96% of patients with two or more malignant features.²⁵ Table 13.1.2 highlights the EEG patterns used.

While fewer studies have been designed to identify predictors of a positive neurologic outcome, the early identification of sleep spindles has been associated with a good outcome in pediatric patients.²⁸ Similarly, while testing practices remain unstandardized, the presence of reactivity—a consistent change in the EEG background pattern in response to auditory, visual, or somatosensory stimuli—appears to be a reliable predictor of a good outcome.^29–31 One possible exception, however, is the presence of stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs). Several studies show SIRPIDs to be associated with a poor prognosis; however, a more recent analysis suggests that SIRPIDs are not a negative predicator per se, but rather are frequently found in association with other, more robust, predictors of a poor prognosis.^32–34

TABLE 13.1.2 ASSOCIATION OF EEG FEATURES WITH NEUROLOGIC OUTCOME

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