Who is Reading your EEG?

Real life cases: a typical month at an epilepsy center …

  • BC is a 66 year-old woman who had a single episode of passing out upon standing after a thyroid biopsy. She first felt dizzy and sweating, and then slumped to the ground. There was no convulsion. Her EEG was read as showing spikes and she was put on a seizure medication. The EEG in question was reviewed and was normal.
  • AH is 70 years old and presented with several weeks of dizziness, headaches and falls. After her EEG showed “ongoing temporal lobe seizures”, she was treated with several seizure medications. Symptoms worsened. The EEG in question was reviewed and was normal.
  • LM is 58 years old and has episodes of left eye throbbing pain and numbness, nausea, poor balance, and feeling hot and sweaty. Her EEG reportedly showed “epileptiform abnormalities”, but her symptoms did not improve with seizure medications. The EEG in question was reviewed and was normal.
  • AA is 22 years old and had episodes of blurry vision when working on her computer. Her EEG reportedly showed spikes she was put on a seizure medication. Her symptoms did not improve. The EEG in question was reviewed and was normal.
  • None of these patients have seizures …

The misdiagnosis of epilepsy is common. About 30% of patients seen at referral epilepsy centers for difficult seizures do not have seizures and have been misdiagnosed. Such a wrong diagnosis of seizures has serious consequences and can in fact be life-changing.

The diagnosis of seizures and epilepsy should be based primarily on a good history. Not EEG. Not MRI. Tests like EEG and MRI can help, but (contrary to a common misconception) should not be the basis for the diagnosis. Nothing replaces the history. In fact most people with epilepsy have normal MRIs and normal EEGs!

A major contributor to the misdiagnosis of seizures is the tendency to over-read normal tracings as abnormal. In fact, as illustrated in the cases above, the episodes in question are often not even suggestive of seizures, and the wrong diagnosis of seizures is often based solely on the “abnormal” EEG. So yes, if there are doubts about your diagnosis of seizures and it is based largely on an “abnormal” EEG, you should question it. Just because one neurologist says an EEG “shows seizures” does not mean it is so.

How big is this problem?

It is difficult to quantify the problem, but all referral epilepsy centers see such patients, and frequently. Furthermore, for one patient whose diagnosis is eventually rectified, there are likely dozens who never are. This of course goes against what is taught at every medical school and during neurology training (“we do not treat the EEG”). It is also why most epilepsy specialists agree that “routine interictal EEG recording is one of the most abused investigations in clinical medicine and is unquestionably responsible for great human suffering” [Chadwick, see references]. Yes, EEG can be bad for you!

The consequences of being misdiagnosed with epilepsy are obvious and serious, including the impact on employment and driving. When the diagnosis is based largely on an abnormal EEG, no amount of subsequent (repeated) normal EEGs will “cancel” the previous abnormal one, and the wrong diagnosis is very difficult to undo. Unlike a CT or MRI scan that is misread, simply repeating it and calling it normal will not cancel the abnormal one, because the EEG is not a test of anatomy and is a sample in time. Only re-review of the actual “abnormal” sample can cancel the misdiagnosis and undo the harm.

The reality is that most EEGs ordered in routine clinical practice (typically for reasons other than seizures) have little or no impact on diagnosis, management and outcome. Most EEGs are also unnecessary (like patient BC above who clearly had a fainting spell). However when it results in a diagnosis of seizures, misinterpretation has serious consequences.

Why are EEGs so commonly over-read?

The main reason is the lack of training and standard in EEG, and the wrong assumption that all neurologists are trained to read EEGs. This assumption could not be further from the truth, as shockingly there is currently no mandatory EEG exposure during Neurology training. In other words, one can become a full-fledged practicing neurologist and have little or no experience in EEG. When one lacks training and experience, it is normal to read “anxiously” and look “too hard” to find abnormalities where there are none. There is also the “fear of missing something” and the (wrong) perception that under-diagnosing seizures would be more harmful than over-diagnosing seizures.

Another reason is that the importance of the EEG is frequently overemphasized, and it is interpreted out of clinical context, as shown in the examples above. The diagnosis of seizures should never be based on the EEG alone when the history does not suggest seizures. Unfortunately, doctors and patients alike tend to have more faith in “tests” than in common sense, which in medicine is called clinical judgment. It is also easier (and more lucrative) to order an EEG than to take a good history.

Thus, as shown in the examples above, the combination of vague, nonspecific symptoms with an equivocal (weak) EEG abnormality is a common cause of wrong diagnoses of seizures.

Possible solutions & recommendations

1. Use a backup or confirmatory interpretation.

This is nearly universal for eletrocardiograms (ECGs). ECGs are routinely read by non-cardiologists (internists, emergency physicians, pediatricians) who can use their interpretations for immediate decisions in managing patients (commonly to determine if chest pain is caused by heart disease). However, as a safeguard against serious errors, a confirmatory and “official” reading by a cardiologist almost always follows. A good argument can be made that we should have the same for EEGs, at least when it comes to a diagnosis of seizures.

2. Define competencies in EEG

Clearly, many neurologists who read EEGs are not adequately trained to do so. So, how do we ensure that neurologists who interpret EEGs are qualified to do so? We should define EEG competency for neurologists who read EEGs, as is done for ECGs. There should be better, more and mandatory EEG training during neurology residency. It would be inconceivable to become an internist without demonstrating some proficiency in ECG interpretation, and in fact, this is specifically addressed in the cardiology and internal medicine fields. For neurologists there are no specific requirements, and “clinical neurophysiology” (which includes EEG) is mentioned together with neuropathology and neuroimaging. However, the enormous difference here is that pathology specimens and neuroimaging studies are not read only by the neurologist. Clinical neurophysiology studies (EEGs, EMGs) are interpreted only by us neurologists. We have the final say.

The American College of Cardiology works together with the American Society of Internal Medicine, the American College of Physicians and the American Academy of Emergency Medicine to raise standards for ECG. Our professional organizations (American Academy of Neurology, American Epilepsy Society, American Clinical Neurophysiology Society) should address this politically difficult situation and work together to raise standards in EEG, in the interest of our patients. Unfortunately our professional societies fear that these potential measures, which would not allow just anyone to read EEGs, may be harmful to the revenue of neurologists. I hope they are not more concerned with the well being of our bank accounts than that of our patients …

Key Points

  • The combination of vague, nonspecific symptoms plus a mis-read EEG is a common cause of wrong diagnosis of seizures.
  • There is no mandatory EEG exposure during Neurology training.
  • EEGs are frequently over-read, i.e. read as “abnormal” when they are really normal
  • If the diagnosis sounds wrong and is based largely or only on the EEG, get another opinion.

References and further reading

  • Benbadis SR. The tragedy of over-read EEGs and wrong diagnoses of epilepsy. Expert Rev Neurother 2010;10:343.
  • Benbadis SR, Lin K. Errors in EEG interpretation and misdiagnosis of epilepsy. Which EEG patterns are over-read? Eur Neurol 2008;59:267–271.
  • Benbadis SR. Errors in EEGs and the misdiagnosis of epilepsy: importance, causes, consequences, and proposed remedies. Epilepsy Behav 2007;11: 257–262.
  • Benbadis SR, Tatum WO. Over-intepretation of EEGs and misdiagnosis of epilepsy. J Clin Neurophysiology 2003;20;42–44.
  • Chadwick D. Diagnosis of epilepsy. Lancet 1990;336:291–295.
  • Ferrie CD. Preventing misdiagnosis of epilepsy. Arch Dis Child 2006; 91:206–209.
  • Hernandez-Frau P, Benbadis SR. Pearls & Oy-sters: Errors in EEG interpretations: What is misinterpreted besides temporal sharp transients? Neurology 2011;76;e57 DOI 10.1212/WNL.0b013e318211c1d5.

Selim R. Benbadis, M.D.
University and South Florida and Tampa General Hospital
Last Reviewed: 7/15/11