Seizures: Pathology review

On the neurology ward, a 7-year old male, called Stefan, is brought by his mother. His mother is worried because he has several episodes every day where he loses consciousness for a few seconds. His teacher also complains that she often catches him daydreaming during the lesson. Next to Stefan, there’s a 17-year old male, called Jacob, who seems sluggish and tired. His friends brought him because he suddenly started “shaking and jerking” and he lost consciousness for about two minutes. His medical history is otherwise insignificant. Now, there’s also an 11-year old female, called Megan, who also seems lethargic. Her father is very upset because he witnessed an episode of twitching of her left foot that lasted a few minutes. Megan was unconscious and has no memory of the event. Finally, there’s a 19-year old female, called Joanna, that has had repetitive episodes of sudden and rapid jerking movements with loss of consciousness for the past few months. They usually occur when she wakes up in the morning and especially during periods of sleep deprivation.

Okay, so all of them had a seizure episode. A seizure is a paroxysmal motor, sensory or autonomic event that occurs due to abnormal, excessive and synchronous electrical discharges from neurons in the brain. Seizures usually last less than 5 minutes. If it lasts more than 5 minutes, it’s called status epilepticus. Epilepsy is a chronic disease of the brain that predisposes an individual to having recurrent unprovoked seizures; that is seizures without a clear triggering cause. Epilepsy is typically diagnosed when an individual has two or more unprovoked seizures separated by at least twenty-four hours.

Okay, now seizures are broadly classified into two types, generalized and focal seizures. Generalized seizures arise from both cerebral hemispheres at the same time, while focal seizures arise from specific areas in one cerebral hemisphere. However, focal seizures can spread to both cerebral hemispheres, causing a generalized seizure. When this happens, it’s appropriately called secondary generalization of a focal seizure.

Okay, now let’s take a closer look at the different subtypes of generalized seizures. Generalized seizures are subclassified into motor and non-motor seizures. Regardless of the subtype, generalized seizures almost always cause a sudden impairment of consciousness. Generalized motor seizures include tonic, clonic, tonic-clonic, atonic, and myoclonic seizures. Tonic seizures involve sudden stiffening of the muscles, while clonic seizures involve rhythmic twitching of the muscles. However, these clinical features are usually combined, so individuals commonly have a tonic-clonic seizure. In a generalized tonic-clonic seizure, a person may have a sudden contraction of their vocal cord muscles, causing them to involuntarily scream or cry during a seizure. Contraction of the ocular muscles can cause uprolling of the eyes. Contraction of the oropharyngeal muscles can impair swallowing, causing respiratory secretions to pool in the oropharynx. Contraction of the jaw muscles may cause the individual to bite on their tongue. Individuals with tonic-clonic seizures may also develop urinary or fecal incontinence. After the tonic-clonic seizure ends, individuals enter a period called the post-ictal phase, during which the individual’s consciousness is still impaired for minutes to hours, so they seem sluggish and tired or hard to wake up. So on the exam, look for these subtle clues that indicate a post-ictal phase. Next are myoclonic seizures. For the test, remember that myoclonic seizures involve sudden, rapid, muscle contractions. This sounds a lot like clonic seizures, but the key difference is that in myoclonic seizures, the contractions are much faster, occurring at a rate of 0.1 seconds, whereas in clonic seizures, the contractions occur at a rate of about 1 to 2 seconds. Myoclonic seizures typically occur in the morning and are usually triggered by stress or sleep deprivation, and that’s something you also have to know for the exams! Alright, now atonic seizures translates to “no muscle tone”. Therefore they are characterized by sudden loss of postural muscle tone lasting 1 to 2 seconds, causing the individual to collapse to the ground out of the blue. Alright, moving on to the other arm of generalized seizures, there are the generalized non-motor seizures. These are called absence seizures and they are very high yield. They are commonly found in children and adolescents. Episodes are characterized by sudden, brief loss of consciousness for seconds to minutes without any change in the individual’s muscle tone. So, they could be sitting in class listening to a lecture and suddenly lose consciousness without falling down. Unfortunately, episodes can occur dozens or even hundreds of times per day, and are classically described by parents and teachers as “staring into space”, or “daydreaming”, or being “inattentive”. In fact, many children with absence seizures are actually misdiagnosed with attention-deficit hyperactivity disorder, because teachers often presume that a child is just not paying attention.