Multiple Sclerosis (MS) is a chronic disease affecting the central nervous system, characterized by the immune system mistakenly attacking the protective myelin sheath surrounding nerve fibers. This damage creates scarring, which disrupts the flow of electrical signals between the brain and the body. Individuals with MS have a higher prevalence of seizures, including focal seizures, compared to the general population. Approximately 3% to 5% of people with MS will experience a seizure, which is roughly three times the rate seen in those without the disease.
Defining Focal Seizures
Focal seizures, previously known as partial seizures, originate from abnormal electrical activity in a specific, restricted area on one side of the brain. They are classified based on the person’s level of awareness during the event, distinguishing them from generalized seizures, which involve both sides of the brain simultaneously.
Focal aware seizures occur when consciousness remains fully intact. Symptoms depend on the brain region affected and may manifest as involuntary twitching of a limb, a sudden sense of déjà vu, or sensory changes like an unusual smell or taste. These episodes are often brief, lasting less than two minutes.
Focal impaired awareness seizures occur when the person’s consciousness is altered or lost. They may appear dazed and unable to respond appropriately to their surroundings. Common behaviors, known as automatisms, can include repetitive actions such as lip smacking, picking at clothes, or aimless wandering. After the seizure ends, the individual may be confused and typically has no memory of the event.
The Neurological Mechanism: MS Lesions and Seizure Risk
The connection between MS and the development of seizures lies in the location and nature of the demyelinating lesions. Seizure generation is fundamentally an issue of neuronal hyperexcitability, which is significantly influenced by damage to the brain’s surface. Lesions situated in or immediately beneath the cerebral cortex—the gray matter responsible for generating electrical activity—are most often associated with seizure activity. Deep brain lesions are less likely to cause this electrical instability.
The chronic inflammation that defines MS damages myelin and nerve fibers in these cortical areas, creating a structural fault line in the brain’s electrical circuitry. This damage alters the local environment, making neurons more prone to firing abnormally.
Following the acute inflammatory phase, the brain attempts to repair itself, which often results in gliosis, a process where scar tissue forms around the old lesions. This scar tissue changes the way electrical signals are transmitted and buffered, disrupting the delicate balance between excitatory and inhibitory signals. Research suggests that astrocytes, which are support cells in the brain, become impaired in their ability to regulate certain molecules like glutamate and potassium ions. Reduced regulation of these compounds contributes directly to the hyperexcitability of neurons.
Clinical Diagnosis and Treatment Approaches
When an MS patient presents with suspected seizure activity, a neurologist’s primary goal is to confirm the diagnosis and identify the underlying cause. The first diagnostic step typically involves an electroencephalogram (EEG), which records the electrical activity of the brain. The EEG helps to confirm whether the symptoms are true epileptic seizures or a different type of transient neurological event, such as a paroxysmal symptom that is common in MS.
High-resolution magnetic resonance imaging (MRI) is used to locate the specific demyelinating plaque that may be acting as the seizure focus. MRI is also necessary to rule out other possible causes for the seizure, such as a stroke, tumor, or infection. The identification of an active or chronic cortical lesion on the MRI provides strong evidence linking the seizure directly to the MS pathology.
Treatment for MS-related seizures relies primarily on anti-epileptic drugs (AEDs), which work to stabilize the electrical activity in the brain. Common medications used include Levetiracetam (Keppra), Lamotrigine (Lamictal), and Carbamazepine, which are generally effective in controlling the seizures. When selecting an AED, neurologists must carefully consider potential side effects like fatigue or cognitive issues, which could compound existing MS symptoms. Furthermore, doctors must ensure that the chosen AED does not negatively interact with any of the patient’s MS disease-modifying therapies (DMTs).