The Dangers of Over-Reading an EEG No abstract available

Normal Awake, Drowsy, and Sleep EEG Patterns That Might Be Overinterpreted as Abnormal Summary: Knowledge of normal patterns is essential for correct EEG interpretation. The overinterpretation of EEG (i.e., ascribing abnormality to EEG patterns that are not associated with disease) is a common problem and can contribute to misdiagnosis and mismanagement. Here, the authors concisely review normal patterns that might be improperly interpreted as abnormal. These include posterior slow waves of youth, central theta, K complexes, asymmetric sleep spindles, hypnagogic and hypnopompic hypersynchrony, arousal patterns, rhythmic midtemporal theta of drowsiness, and the wicket rhythm. Recognition of these patterns will lead to greater accuracy in EEG interpretation and help avoid incorrect management.

Normal Variants Are Commonly Overread as Interictal Epileptiform Abnormalities Summary: Electroencephalographers may misclassify benign variant EEG patterns as epileptiform discharges, resulting in delays in the diagnosis and appropriate treatment of other paroxysmal disorders, such as psychogenic nonepileptic seizures, anxiety/panic disorders, and near syncope. These benign variant patterns include wicket spikes, small sharp spikes, and rhythmic mid-temporal theta of drowsiness. Cautious interpretations of semi-rhythmic sharp transients, usually gradually rising from the EEG background in drowsiness, can help avoid misdiagnosing patients as having seizures. Viewing the EEG as confirmatory for a clear clinical diagnosis is also helpful—elderly patients with syncope, for example, often have microvascular disease and EEG wicket rhythms in drowsiness—a careful review of the clinical history and the paroxysmal EEG pattern usually help distinguish normal variant patterns from interictal sharp waves and spikes and avoid misdiagnosing epilepsy.

Artifacts That Can Be Misinterpreted as Interictal Discharges Summary: It is presumed that the EEG records only cerebral activity. However, frequently it can include other electrical activities, referred to as noise or artifact, which are not of cerebral origin. In the last few decades, evolution in digital technology has greatly improved the ability to record and display interpretable EEG. With the widespread availability of prolonged EEG recording, new artifacts have been described. The addition of concomitant video with audio during recordings has allowed in most instances to determine the source of certain artifacts. One of the challenges of interpreting EEGs consists of identifying artifacts correctly. Some of the EEG artifacts are so distinctive in appearance that the experienced reader can readily identify them. It is not uncommon for normal EEGs to be overinterpreted, especially by inexperienced readers. Failing to identify artifacts correctly can lead to “over reading” a study and doing so can result in misdiagnosis of epilepsy. This in turn can result in inappropriate treatments that ultimately can have serious clinical implications. This review will provide a description of the most commonly encountered artifacts that mimic spike or sharp waves, also referred to as interictal epileptiform discharges. In addition, we will describe troubleshooting approaches to eliminate these artifacts whenever possible. Artifacts that mimic ictal discharges will be reviewed in a different section.

Artifact Mimicking Ictal Epileptiform Activity in EEG Summary: Although the EEG is designed to record cerebral activity, it also frequently records activity from extracerebral sources, leading to artifact. Differentiating rhythmical artifact from true electrographic ictal activity remains a substantial challenge to even experienced electroencephalographers because the sources of artifact able to mimic ictal activity on EEG have continued to increase with the advent of technology. Knowledge of the characteristics of the polarity and physiologic electrical fields of the brain, as opposed to those generated by the eyes, heart, and muscles, allows the electroencephalographer to intuitively recognize noncerebrally generated waveforms. In this review, we provide practical guidelines for the EEG interpreter to correctly identify physiologic and nonphysiologic artifacts capable of mimicking electrographic seizures. In addition, we further elucidate the common pitfalls in artifact interpretation and the costly impact of epilepsy misdiagnosis due to artifact.

Patterns Specific to Pediatric EEG Summary: Misinterpretations of the EEG can result in erroneous diagnosis of epilepsy, causing considerable family anxiety, over protectiveness of children, and delays in normal development and developmental exploration. The burden of a chronic disease can result in expensive and unnecessary medical treatment. The misdiagnosis of epilepsy has been well documented in adults, but misdiagnosis in normal children can have a long-lasting impact on their health. Furthermore, the EEG has a wider range of morphology and hence a greater opportunity for the missed diagnosis of epilepsy. Lack of familiarity of normal sleep patterns and age-related changes from the premature neonate to the young child make children particularly susceptible to misdiagnosis of epilepsy.

The Role of EEG in the Erroneous Diagnosis of Epilepsy Summary: Errors in diagnosis are relatively common in medicine and occur in all specialties. The consequences can be serious for both patients and physicians. Errors in neurology are often because of the overemphasis on "tests" over the clinical picture. The diagnosis of epilepsy in general is a clinical one and is typically based on history. Epilepsy is more commonly overdiagnosed than underdiagnosed. An erroneous diagnosis of epilepsy is often the result of weak history and an "abnormal" EEG. Twenty-five to 30% of patients previously diagnosed with epilepsy who did not respond to initial antiepileptic drug treatment do not have epilepsy. Most patients misdiagnosed with epilepsy turn out to have either psychogenic nonepileptic attacks or syncope. Reasons for reading a normal EEG as an abnormal one include over-reading normal variants or simple fluctuations of background rhythms. Reversing the diagnosis of epilepsy is challenging and requires reviewing the "abnormal" EEG, which can be difficult. The lack of mandatory training in neurology residency programs is one of the main reasons for normal EEGs being over-read as abnormal. Tests (including EEG) should not be overemphasized over clinical judgment. The diagnosis of epilepsy can be challenging, and some seizure types may be underdiagnosed. Frontal lobe hypermotor seizures may be misdiagnosed as psychogenic events. Focal unaware cognitive seizures in elderly maybe be blamed on dementia, and ictal or interictal psychosis in frontal and temporal lobe epilepsies may be mistaken for a primary psychiatric disorder.

Quantitative EEG Biomarkers for Mild Traumatic Brain Injury Purpose: The development of objective biomarkers for mild traumatic brain injury (mTBI) in the chronic period is an important clinical and research goal. Head trauma is known to affect the mechanisms that support the electrophysiological processing of information within and between brain regions, so methods like quantitative EEG may provide viable indices of brain dysfunction associated with even mTBI. Methods: Resting-state, eyes-closed EEG data were obtained from 71 individuals with military-related mTBI and 82 normal comparison subjects without traumatic brain injury. All mTBI subjects were in the chronic period of injury (>5 months since the time of injury). Quantitative metrics included absolute and relative power in delta, theta, alpha, beta, high beta, and gamma bands, plus a measure of interhemispheric coherence in each band. Data were analyzed using univariate and multivariate methods, the latter coupled to machine learning strategies. Results: Analyses revealed significant (P < 0.05) group level differences in global relative theta power (increased for mTBI patients), global relative alpha power (decreased for mTBI patients), and global beta-band interhemispheric coherence (decreased for mTBI patients). Single variables were limited in their ability to predict group membership (e.g., mTBI vs. control) for individual subjects, each with a predictive accuracy that was below 60%. In contrast, the combination of a multivariate approach with machine learning methods yielded a composite metric that provided an overall predictive accuracy of 75% for correct classification of individual subjects as coming from control versus mTBI groups. Conclusions: This study indicates that quantitative EEG methods may be useful in the identification, classification, and tracking of individual subjects with mTBI.

Preoperative Evaluation of Iatrogenic Spinal Accessory Nerve Palsy: What Is the Place for Electrophysiological Testing? Purpose: Electrophysiological testing has been used for the early diagnosis of iatrogenic spinal accessory nerve palsy in clinical practice. However, the presence of low-amplitude compound action potential in 70% to 90% of the patients suffering from iatrogenic nerve transection was reported in several studies. We have encountered the same issue and made minor modifications to the methods of electrophysiological testing. The purpose of this study was to retrospectively evaluate the reliability of our modified electrophysiological testing as preoperative examination in patients receiving surgical revision. Methods: In this study, we compared preoperative electrophysiological testing results with intraoperative diagnosis in the 24 patients with iatrogenic spinal accessory nerve palsy who were referred to our hospital from 2009 to 2018. Results: During operation, 20 patients were diagnosed with neurotmesis and the remaining 4 patients were found axonotmesis depending on the results of surgical exploration and intraoperative electrophysiological examination. Six of the 20 patients with neurotmesis demonstrated a low-amplitude compound muscle action potential of the upper trapezius during preoperative electrophysiological testing. Needle electromyography revealed voluntary motor unit potentials in 8 of the 20 patients. Meanwhile, concomitant great auricular nerve or dorsal scapular nerve injuries were preoperatively revealed in 7 of 24 patients. Conclusions: The rate of low-amplitude compound muscle action potentials in these patients suffering from spinal accessory nerve neurotmesis was about 30% with our modified electrophysiological testing. We should be aware of this pitfall before surgical nerve repair. Furthermore, electrophysiological testing is an informative preoperative examination revealing the concomitant nerve injuries.

Role of Ultrasonography in Severe Distal Median Nerve Neuropathy Purpose: Electrodiagnostic studies do not differentiate severe lesions of the median nerve in the distal forearm from those within the carpal tunnel when compound muscle action potential over the abductor pollicis brevis and sensory nerve action potential are absent; needle electromyography showing denervation confined to the abductor pollicis brevis is presumed to suggest localization to the carpal tunnel, although the lesion may be in the forearm. Under these circumstances, the patient may undergo carpal tunnel release without benefit. This retrospective study looked at patients with clinical picture of severe carpal tunnel syndrome who had no compound muscle action potential or sensory nerve action potential on median nerve stimulation; the goal was to determine how often ultrasonic imaging pointed to a location other than the carpal tunnel. Methods: Patients with clinical picture of severe carpal tunnel syndrome with no sensory nerve action potential and no compound muscle action potential over the abductor pollicis brevis and second lumbrical underwent ultrasonic imaging; criteria for localization to the carpal tunnel included significant increase in the cross-sectional area of the median nerve at the carpal tunnel inlet and increase in the wrist/forearm cross-sectional area ratio. Results: In 42 of 46 cases, entrapment at the carpal tunnel was confirmed by ultrasonography; in four patients, other causes were located proximal to the carpal tunnel. Conclusions: Ultrasonic imaging is useful not only for confirming entrapment of the median nerve at the carpal tunnel in patients with nonlocalizing electrodiagnostic studies but also in detecting pathology in the forearm, which may mimic severe carpal tunnel syndrome.