Abnormal brain activity – not yet epilepsy
Almost a century and a half ago, in May 1873, Hans Berger, the discoverer of the alpha rhythm of the human brain and the creator of the electroencephalography method, was born in Germany. It should be noted that the very fact of the generation of an electric current by the brain was discovered by the Englishman Richard Caton. But it was Berger who, in 1924, was able to register for the first time on a paper tape using a galvanometer, electrical signals taken from the surface of the head without penetrating the brain. And after he presented the first description of the encephalogram in 1929, a new era began in epileptology .
Today, the electroencephalography (EEG) method is widely used by neurologists and other doctors who deal with diseases of the central nervous system – in particular, the brain. EEG is a mandatory diagnostic tool for epilepsy. Therefore, the referral to the EEG is received by people whose profession implies the exclusion of this disease. And sometimes a completely healthy person unexpectedly receives the results of an examination with a mysterious and frightening phrase “Signs of epileptiform activity have been found.”
What is epilepsy?
Epilepsy is a disorder of the central nervous system in which abnormal activity in the brain develops, leading to seizures, periods of unusual behavior and sometimes loss of consciousness.
Outwardly, the manifestations of a seizure may look different: some people develop convulsions in the form of twitching of the limbs, others “freeze”, “turn off” from reality for a few seconds.
A single case of a seizure does not mean that a person has epilepsy, but two or more apparently unprovoked seizures are already a reason for a diagnosis. At the same time, the problem of diagnosing epilepsy has been faced by neurologists throughout the entire time of acquaintance with this disease.
Overdiagnosis of epilepsy
Overdiagnosis of epilepsy, that is, the detection of it in people who actually do not get it, is not so rare. In the 1980s, doctors said that 20-25% of newly diagnosed epilepsy cases were overdiagnosed. Underdiagnosis , that is, a situation when a person has epilepsy, but cannot be diagnosed, is much less common – only in 10% of cases.
It would seem that there is such a wonderful method as electroencephalography – what prevents from accurately diagnosing epilepsy? The most common mistake, as it turns out, is the problem of diagnosing epileptiform activity of the brain.
Epileptiform activity of the brain
As the name suggests, this activity is suspiciously similar to that of epilepsy. On the encephalogram, it represents electrical vibrations that look like sharp waves and peaks that differ by 50% or more from the so-called background activity of the brain. The same peaks in most cases can be found on the encephalogram of people with epilepsy. The cause of epileptiform activity is the summation of potentials, both inhibitory and excitatory, which are associated with a powerful neuronal discharge and neuronal hyperpolarization .
The very term “epileptiform activity” often misleads patients. Neurologists themselves have already agreed that in describing the encephalogram one should avoid such terms as “epileptic activity” or “convulsive discharge”, as well as “paroxysmal discharge” and “increased convulsive readiness”, so that it does not frighten patients. And “epileptiform activity” was recognized as the most correct term, which, however, for an ordinary person, thanks to the prefix “epi-“, still sounds menacing.
Epileptiform activity in people with epilepsy
It is important to understand that epileptiform activity is not always manifested in people with epilepsy. As well as not always it is registered in those who have this diagnosis. The frequency of its detection in the latter case during routine (that is, not associated with attacks) examination is 29-55%.
Confirmation of epilepsy is possible by conducting several repeated EEGs against the background of targeted sleep deprivation (sleep deprivation) – in this case, epileptiform activity in patients with epilepsy will manifest itself in 80% of cases. EEG recording during sleep allows detecting epileptiform changes with a frequency of 85-90%. Finally, during an attack, a similar pattern on the encephalogram is observed in 95% of cases.
Note that in rare situations, when abnormal activity of neurons develops deep in the cortex , electrical impulses may not be reflected on the surface of the brain and even against the background of an ongoing epileptic seizure may not be recorded in any way.
Abnormal brain activity without epilepsy
People who do not have epilepsy, as mentioned above, can also show epileptiform activity. Often this happens in situations of the same routine examination. For example, many professions require a medical record, and the list of doctors that must be passed includes a neurologist, and the list of tests and examinations includes an encephalogram. Experts from clinics dealing with the execution of this kind of documents report that cases of detection of epileptiform activity during encephalography in a person who is actually healthy do not happen so rarely.
Where does the abnormal activity of neurons in the brain come from if a person does not have epilepsy? Well, for example, some people have a genetic predisposition to the epileptiform activity of brain neurons, but at the same time they are not susceptible to it in the form of a convulsive epileptic seizure.
So, epileptiform activity was detected in 0.5% of cases among young people 17-25 years old – students of educational institutions of the British Air Force. Moreover, in 58% of cases, abnormal brain activity was observed only as a result of rhythmic photostimulation – this is the name of the procedure for influencing the patient with the help of light flashes flashing in a certain rhythm.
Epileptiform activity during EEG recording during sleep can also be detected in 2% of adults who do not suffer from epilepsy.
More often, epileptiform activity is found in children who do not have epilepsy. So, in 2-5% of children aged 6-13 years, epileptiform changes can be detected on the EEG. And only 3.5-8% of them subsequently develop epilepsy.
Even more often (in 10-30% of cases) epileptiform activity occurs in people after a stroke, with brain tumors and traumatic brain injuries, and with various congenital brain defects. And only 14% of these patients develop epilepsy in the future.
Certain types of epileptiform activity can also be found on the EEG in people with metabolic encephalopathies ( hypocalcemia , thyrotoxicosis, uremic and Hashimoto’s encephalopathy , etc.) and in patients with chronic renal failure.
Finally, some drugs, especially at high dosages: lithium, chlorpromazine, and clozapine , can cause epileptiform activity . Cancellation of previously taken barbiturates gives a similar result.