Continuing Education Activity

Electroencephalogram (EEG) is a method of providing high temporal resolution of the cortical neuronal activity of the brain. The EEG waveforms represent the summation of excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP) of cortical neurons. It is essential to accurately differentiate the benign and pathological variants of EEGs. Precise recognition of benign variants of the EEG is crucial to avoid an errant diagnosis of epilepsy. The breach rhythm, also known as the breach effect, is a benign EEG pattern with an epileptiform morphology caused by a focal skull abnormality. A focal skull defect, such as after craniotomy or cranial surgery, can cause an increase in the amplitude of alpha, beta, and mu rhythms, leading to the breach effect. This activity reviews the cause, pathophysiology, and presentation of the breach rhythm and highlights the role of the interprofessional team in accurately recognizing it.

Clinicians participating in this CME activity can expect to gain comprehensive insights into the EEG and its role in assessing cortical neuronal activity. Participants will enhance their ability to identify breach rhythms, particularly when occurring in serial trains, and learn to differentiate them from spike-like epileptiform activity. The significance of precise rhythm interpretation in improving patient care outcomes and safety is emphasized throughout this educational review.

Objectives:

• Identify the causes of breach rhythm.

• Differentiate breach rhythm from epileptiform activity, recognizing key characteristics and irregular morphology in EEG waveforms.

• Implement evidence-based protocols for breach rhythm interpretation, integrating updated guidelines into clinical practice for accurate diagnosis.

• Collaborate with an interprofessional team to improve care coordination and outcomes for patients affected by breach rhythm.

Introduction

The breach rhythm, also known as the breach effect, is a benign electroencephalogram (EEG) pattern with high voltage, often spiky and irregular morphology that can resemble an epileptiform morphology caused by a focal skull abnormality. A focal skull defect, such as after a craniotomy, can cause an increase in the amplitude of alpha, beta, and mu rhythms, leading to the breach effect. Breach rhythm and epileptiform activity in the same area can be challenging to differentiate. Breach rhythm typically has sharp contours and irregular morphology and usually has a frequency of 6 to 11 Hz but may be associated with faster or slower wave activity. It may sometimes be hard to differentiate from actual epileptiform activity in the same area, which can lead to under- or overdiagnosis of epilepsy and thus can have significant clinical consequences.[1][2][3]

EEG Features of Breach Rhythm

An EEG is a noninvasive test for providing neurophysiological activity of the brain. It is usually done by placing electrodes over the scalp to measure the activity of cortical neurons.[4] The EEG waveforms are the summation of EPSP and IPSP of cortical neurons. It is essential to understand how to differentiate between normal/benign variants of EEG vs pathological variants of EEG. The benign variants of EEG are considered normal but can be confused with epileptiform activity. Accurate recognition of benign variants in the EEG is crucial to avoid an errant diagnosis of epilepsy.[5]

Breach rhythm typically is a focal, asymmetrical, high-voltage EEG activity. It often has arch-like waveforms, sometimes having spiky morphology. It can manifest as an irregular rhythm, sometimes associated with sharp activity.[2] Breach rhythm is most prominent when recorded over central and temporal regions. Breach rhythm can be identified easily when it occurs in serial trains. Single, spike-like, or sharp-contoured waveforms are more likely to be mistaken for epileptiform activity. These waveforms should be compared with waveforms of the rhythmic activity constituting breach rhythm to determine if these are distinct waveforms or similar to those constituting the breach rhythm. The absence of after-coming slow-wave components and lack of spread to other areas is characteristic of breach rhythm. Brain damage should be suspected if breach rhythm is associated with polymorphic delta activity.[6] If the breach rhythm is located over the central region, it can be blocked by physical movement due to the presence of an underlying normal mu activity. Breach rhythm can sometimes persist during sleep. It can manifest as a voltage increase in spindles in stage 2 of sleep.[2]

Etiology

The breach effect occurs due to an increase in the amplitude of alpha, beta, and mu rhythm activity over or near an area of a bony defect on the skull, usually a postsurgical craniotomy site. The skullbone normally acts as a filter for brain electrical activity, and it selectively attenuates the higher frequencies. An increase in amplitude and frequency of the breach effect is due to decreased electrical impedance caused by reduced filtering from the skull defect. Small skull defects, for example, a burr hole, is unlikely to produce a breach effect, as the field detected by each electrode is larger than the hole.[1][2]  There are also reports of breach rhythm being related to the functional state of underlying brain tissue.[7] Lyudmilov et al noticed that after a seizure event in a patient with a craniotomy, the EEG revealed subclinical seizure patterns until an antiseizure medication suppressed these, and then a breach rhythm was observed. It was noted that a breach rhythm could be suppressed due to Todd's paralysis/postseizure subclinical activity [7].

In some instances of astrocytoma, there have been reports that either attenuation or loss of the breach rhythm can be an initial sign of tumor progression.[8] There are also reports of breach rhythm being developed over a solitary skull lesion due to multiple myeloma.[9]

Epidemiology

Breach rhythm is a rare benign variant of EEG. The epidemiology of breach rhythm is unknown.

Pathophysiology

Breach rhythm was described in 1979 by Cobb and associates. Breach rhythm refers to a change in the transmission of EEG waves through a skull defect. Bone offers major resistance between the cortex and scalp electrodes. One square centimeter of the skull provides approximately 40,000 ohms of resistance, the dura mater about 12,000 ohms, and the scalp about 1000 ohms of resistance. Therefore, there is a significant increase in electrical activity from the cortex to the scalp when these resistors are absent. The final results of the absence of these resistors are the spiky, sharply-contoured waveforms of the breach effect. Breach rhythm is most prominent in the central and temporal regions.[1][2][10]

Breach rhythm is not due to abnormality of the brain; it is due to a skull defect. The defect can be the result of surgery or, rarely, a large osteolytic bony skull lesion, such as in multiple myeloma.[9][11]

History and Physical

Obtaining a surgical history relative to the skull and a history of brain trauma is essential. Skull defects can be missed on palpation because an acrylic material may have replaced a skull defect. Bipolar montage may better identify the breach rhythm due to its higher spatial resolution.[2]

Evaluation

Identifying breach rhythm while interpreting EEG is vital to avoid misinterpretation of epileptiform activity.

It is important to inquire about the patient's surgical history and any history of head trauma to evaluate if a breach rhythm is likely to be present. Palpation of the scalp may not be sufficient. Breach rhythm is seen over skull defects and abruptly diminishes beyond the margin of the defect. It is best appreciated by bipolar montage due to its higher spatial resolution.[2]

Breach rhythms typically are high voltage waveforms between 6 to 11 Hz, often mixed with waves of higher and lower frequencies, including beta, mu, or theta activity. They often appear as a high-amplitude spiky or sharply contoured activity similar to epileptiform activity. Pure breach rhythms do not have an after-going slow wave. There is no spread of activity to other areas of the brain. Sleep recordings can aid in the differentiation between breach rhythm and epileptiform activity, although breach rhythms can affect both awake and sleep rhythms.[1][2]

In general, interictal epileptiform abnormalities are facilitated during NREM sleep and inhibited during REM sleep. If breach rhythm is constituted mostly by enhanced underlying rhythms, breach rhythm will attenuate or disappear during drowsiness and sleep. It may linger into drowsiness and light NREM sleep if the breach rhythm is mixed with a mid-temporal, alpha-like rhythm. Mu rhythm within breach rhythm can be tested for reactivity by asking the patient to move the contralateral limb. Attenuation suggests reactivity of breach rhythm and is indicative of a normal pattern; however, lack of reactivity does not rule out the presence of normal rhythm.[2][1]

EEG filters should be used carefully. Filters to reduce too-high frequency may filter out the higher frequencies of breach rhythm, but the left-out activity could resemble spikes or sharp waves. Muscle artifacts usually can be easily identified by their much higher frequency component, provided an appropriate high-frequency filter is chosen. Filtering out muscle activity will attenuate the signals and may be confused for epileptiform abnormalities within the breach rhythm.[1][10][2]

Treatment / Management

Breach rhythm is a benign variant and does not warrant treatment. The attenuation of preexisting high amplitude and/or the presence of focal slow waves on serial EEG recordings may suggest progression of the lesion beneath the skull defect. On the other hand, it is also important not to miss actual epileptiform activity on top of a breach rhythm. The presence of slow waves in the delta range and an electrical field associated with the abnormality must be recognized as real underlying pathology.

A "conservative" reading is encouraged by most specialists since most believe that over-reading is likely more harmful than under-reading.[2] When in doubt, brain imaging with CT and/or MRI of the head can be used to determine if any focal lesion is causing seizure activity.

Differential Diagnosis

It is important to differentiate the breach rhythm from interictal epileptiform discharges by scrutinizing the surrounding background activity.[12][13] Polyphasic interictal discharges are complex with a slow wave and have a characteristic morphology that does not resemble the background activity.

Interictal epileptiform discharges include the following:

• Paroxysmal fast activity
• Beta frequency activity
• Electromyographic (EMG) artifact [14]

The breach effect has a clearly circumscribed region of increased amplitude. The paroxysmal fast activity appears in bursts with an intervening return to the asymmetric baseline.

Breach rhythm can be differentiated from beta activity by its distribution. Normal beta activity is bilateral but may vary in distribution. 

EMG artifacts occur in regions with overlying muscle, most commonly frontal and temporal regions. EMG artifacts can be differentiated by their inconsistent presence and significantly higher components.[10][2]

Prognosis

As breach rhythm is a benign variant, the prognosis is excellent.

Complications

The failure to distinguish breach rhythm from epileptiform abnormalities can lead to misinterpretations and complications. The breach effect's sharply contoured morphology may be mistakenly perceived as an epileptiform abnormality, resulting in a misdiagnosis of epilepsy and unnecessary antiepileptic drug treatment. Conversely, epileptiform abnormalities occurring in the same area as breach rhythm may be overlooked, leading to undiagnosed cases. Hence, a precise and accurate interpretation is crucial due to its significant clinical implications.

Deterrence and Patient Education

Correctly identifying EEG artifacts and normal patterns can help avoid overinterpretation and misdiagnoses of epilepsy, preventing adverse clinical consequences. The critical skill of differentiating between benign and pathological variants of EEG is crucial for accurate evaluations. 

Pearls and Other Issues

• Breach rhythm is due to a skull bone abnormality or defect and not due to brain pathology.                                          
• Breach rhythm can be mistaken for epileptiform activity.                                                                                      
• An important distinction between breach rhythm and epileptiform abnormality is the absence of an after-coming slow wave and the lack of spread to other areas of the brain.                                                           
• Breach rhythm occurs over the area of the skull defect and abruptly disappears at the margin of the skull defect.                                                                                                                                                             
• Breach effect can affect both awake and sleep rhythms.

Enhancing Healthcare Team Outcomes

Health professionals, including physicians, advanced care practitioners, and nurses, need honed skills in accurately interpreting EEG patterns, specifically distinguishing breach rhythm from epileptiform activity. Clinicians and EEG technicians should always ask the patient about any history of brain surgery or head injury before performing and interpreting the EEG.[1][2][10] Proficiency in utilizing advanced diagnostic tools such as brain imaging is crucial to confirm breach rhythm suspicions and rule out other potential causes.

A strategic approach involves implementing evidence-based protocols and guidelines for breach rhythm interpretation, ensuring standardized practices across healthcare teams. Developing strategic care plans tailored to individual patient presentations enhances team performance and improves patient management. Care coordination involves aligning efforts across various healthcare professionals to streamline the diagnostic process.

Healthcare professionals are responsible for staying updated on the latest advancements in breach rhythm diagnosis and contributing to continuous quality improvement. Coordinated efforts prevent gaps in care, reduce redundancy, and enhance the overall patient experience.