Occipital epilepsy is a neurological disorder that arises from excessive neural activity in the occipital lobe of the brain that may or may not be symptomatic. Occipital lobe epilepsy is fairly rare, and may sometimes be misdiagnosed as migraine when symptomatic. Epileptic seizures are the result of synchronized neural activity that is excessive, and may stem from a failure of inhibitory neurons to regulate properly.[1]
It is a disorder with focal seizures in the occipital lobe of the brain. There are two main types of this epilepsy, each consisting of focal seizures- Gastaut and Panayiotopoulos (Pan.).[2] Other names for the Gastaut type include benign epilepsy of childhood with occipital paroxysms (BECOP) and late-onset occipital epilepsy. Pan. is also known as self-limiting focal epilepsy of childhood with occipital paroxysms and early-onset benign partial epilepsy with occipital paroxysms. There may be no known cause of this type of seizure, but these epilepsies may occur for a variety of reasons, such as brain tumors, infection, trauma and lesions, and idiopathic onset.[3] Seizures originate in the occipital lobe and account for 5 to 10 percent of all epileptic seizure types. Generally, this type of epilepsy can have an onset anywhere from 1–17 years old in children, but the patient prognosis is good. Since the event is located in the occipital lobe, symptoms may occur spontaneously and include visual stimuli.
Signs and symptoms
In occipital epilepsy, the hallmark symptoms include both visual and oculomotor. Symptoms may happen spontaneously, or be due to a lesion or injured area of the occipital lobe.[4] For visual symptoms, these may include simple to complex hallucinations, blindness, visions, and palinopsia (seeing a visual stimulus after it has been removed from the visual field). These are usually brief, but can be experienced from 1–3 minutes. Oculomotor symptoms include tonic deviation of the eyes, nystagmus (rapid, involuntary movement of the eyes) and repetitive fluttering or closing of the eyelids.[5] In children, they may also have nausea and vomiting during the episode as well.[3] Episodes in total for children usually last less than 10 minutes, and mainly occur at night. Triggers can include turning off lights, and going between dark to light or light to dark areas.[6] It is not uncommon to experience postictal headache, extremely similar to migraines after these seizures. Occipital epilepsy can cause many seizures per day and often in multiple clusters. The seizures may also spread to other areas in the brain.
Spreading of the seizures can move to the anterior regions, causing symptoms also from the frontal, temporal, and parietal lobes, and secondary hemi convulsions or convulsions.[5] There are also subtypes to occipital lobe seizures caused by the spread within the brain and where exactly the seizure is occurring in the occipital lobe, causing variation of symptoms.
1. Primary visual cortex- can cause visual hallucinations and visions, or blindness in a certain area or completely
2. Extra-striate cortex- more complex hallucinations such as people, places, or animals
This type primarily affects vision and may cause partial vision loss, a sensation of flashing lights, multi-colored spots and shapes, hallucinations (rare), jerking on one side of the body, and headaches during or after the seizure.[2]
Panayiotopoulos syndrome
The main seizure type of this classification of occipital epilepsy is known as autonomic due to the symptoms experienced such as turning pale, feeling ill, and usually vomiting, dilation of pupils, sweating, drooling, and watering of the eyes. Children may become unresponsive with their head fixed to one side, which can last up to 20–30 minutes. Jerking of the limbs on one or both sides of the body is also very common. Most will sleep after the event. Interestingly, over two-thirds of these seizures occur during sleep, whether it be at night or during a daytime nap, but usually are not very frequent- typically one or two every few months.[2]
Cause
Some causes for occipital lobe epilepsy can be a lesion and/or injury to the occipital lobe. If that is not the case, the cause often may be unknown.[4] Other potential causes could be tumors or cortical malformations. Lesions can be due to occipital cortical dysplasia, which can be difficult to identify and diagnose based on an MRI. Most commonly, the disorder is due to idiopathic occipital epilepsies in childhood, and other rare syndromes affecting the occipital area is Sturge-Weber syndrome, adult forms of Rasmussen's syndrome, and more.[8]
Mechanism/Pathophysiology
Technically speaking, occipital epilepsy is caused by the disruption of the auto-regulation of the posterior cerebral circulation, with resulting cerebral edema in the supra-tentorial white matter and cortico-medullary region.[8] Normally, the neurons are constantly communicating with one another in the brain tissue, via electrical signals. A seizure occurs when this communication is disrupted, and the brain area receives a burst of abnormal electrical signaling, interrupting the normal function.[9] This causes disturbed messages to be sent to other parts of the brain, in turn causing the symptoms of a seizure and can include changes in behavior, consciousness, movements, or feelings.
The disorder of electrical signals causes excessive excitation or loss of inhibition, which is a function of malfunctioning ion channels, as neurotransmitters are released in an unorganized fashion. Even isolated and brief seizures negatively affect the brain. Repeated seizures, such as in occipital epilepsy, can cause extensive brain damage in the occipital lobe, as well as other regions.[7]
When the brain detects that a pathway in the brain is not being used, or it is malfunctioning, the brain attempts to rewire, or to kill the cells involved in that pathway. If a specific region is where the seizure is located, the brain will continue to try to make changes in that area, causing increased symptoms for that individual. More so, as seizures spread throughout the rest of the brain, those areas may also begin to have tissue damage, leading to further seizures and symptoms.[9]
Diagnosis
Epileptic waves during a seizure on an EEG
Procedures for diagnosis of occipital epilepsy include hematology, biochemistry, screenings for metabolic disorders, DNA analysis, and most commonly, MRI. Electroencephalogram (EEG) is also used to detect abnormal brain waves and activity that is reflected as slow waves, or spikes on the recordings. For occipital epilepsy, commonly identified abnormalities on the EEG when a seizure is not occurring (inter-ictal) includes posterior lateralized slow waves, asymmetrical alpha and photic following, and unilateral occipital spikes. Idiopathic cases may appear mostly normal, with occipital spikes or paroxysms. Ictal EEG's show occipital paroxysmal fast activity, spiking, or both, as well as brief occipital flattening. About one-third of occipital seizures do not show any obvious changes.[5]
An MRI would be performed to look at any lesions, damage, or abnormalities in the occipital region of a patient's brain. More specifically, a functional MRI, or fMRI, can detect changes in blood flow throughout the brain when specific parts of the brain are being used. Blood tests and other hematological assays can check for any signs of infection, genetic conditions, or other conditions that could be causing seizures. Computerized tomography (CT) can also be used to detect any abnormalities such as tumors, lesions, bleeding, or cysts.[10] Based on all of these techniques, a provider would conclude if it appears that there has been seizure activity in a patient's brain, where it is located, and the severity of the condition, based on any existing tissue damage.
Prevention and Treatment
The detailed mechanism of epilepsy has not been completely understood, but various anti-epileptic drugs can have a significant effect in reducing symptoms. These work by taking action on voltage-dependent sodium, calcium, and potassium channels, as well as GABA and excitatory receptors, various enzymes, and synaptic proteins. One example that is commonly diagnosed as treatment is carbamazepine. This drug works to block voltage-dependent sodium channels, making fewer available to open.[11] Although not very widely performed or well researched for many patients with occipital epilepsy, surgical intervention to remove the area with seizure activity is also an option for patients.
Preventions are slim for this condition, but it is important to strive to have a healthy pregnancy, stay up to date on all vaccinations, prevent head trauma and injury, and wash their hands regularly to prevent infections that may affect the brain.[12]
Prognosis
Like any type of epilepsy, there are many factors contributing to prognosis. The frequency of seizures, the severity of damage and symptoms, and the individual's response to treatment can vary from a relatively good outlook to a progressive decline. This is also dependent on the underlying cause of epilepsy.[5] If the cause is a previous lesion or trauma, there are likely many other factors and conditions that play into that patient's prognosis.
For many children with one of these types of occipital epilepsy, it is possible to live a normal adult life and to wean off of their anti-epileptic drugs. Based on current research, it seems very rare for a child to continue to have or restart having seizures in their adult life.[2] Seizures typically begin getting better, allowing weaning off of medications around age 15–16. However, it is possible in 5-10% of young people, for them to need to stay on the drugs to prevent seizures. For brain function, most occipital epilepsy patients have normal experiences throughout their education, although a few may have minor difficulties with learning.[2]
Epidemiology
Occipital epilepsy occurs equally in males and females and can occur at any age, although most patients’ onset begins in childhood. OE accounts for 5-10% of epilepsies, as it is a rare syndrome. Again, the age of onset varies based on the classification of OE a patient has. For Gastaut syndrome, the typical onset of symptoms is between ages three and seven, while Pan. has a later onset of 6–13 years old on average.[2]
Research Directions
Currently, there are several studies going on researching the effectiveness of anti-epileptic drugs. Additionally, more is being researched about surgical options, and postoperative success in these patients.[13] Similar to many conditions rooted in the brain, a more clear picture of the brain and its map also needs to be compiled to help aid surgical studies.[14] Scientists are also trying to determine a more clear differential in diagnosis of occipital epilepsy, specifically distinguishing it from migraines.
One study found that the visual stimuli differs in OE versus migraines. In a sample population of persons with OE, the predominant symptom was usually a colorful, circular visual pattern, with the most common colors being bright red, yellow, blue and green. Rarely was there a single visual stimulus, and the size of the hallucinations varied from spots to small balls.[15] In migraines, the visual symptoms usually begin with a small sparkling, shimmering area that expands slowly, and often has jagged edges.[16]
Other research is investigating potential links between OE and other disorders. One such study found that an increased frequency of Celiac Disease has been reported in OE, and that there is increased prevalence of CD in OE patients so more research needs to be performed to look into a potential link between these two disorders.[17]
Additionally, scientists are attempting to use established knowledge about other types of epilepsies in order to compare with OE. Santagelo, et al. wanted to compare the cognitive profiles of OE patients, versus temporal lobe epilepsy (TE) patients. They focused on memory, visuospatial functions, and executive functions through a battery of tests on these patients. It was found that OE patients performed better than TE on verbal long-term memory testing, and TE patients performed better on visuospatial function tasks. They concluded that dysfunction in visual and spatial organization is related to OE diagnosis, and supports disruption in the occipito-parietal stream.[18]
These studies and others do help in the narrowing of diagnosis and the broadening of understanding OE, but a more specific set of criteria, treatment, and diagnosis for the specific subtype of occipital epilepsy is also necessary to continue increasing patients’ prognosis.
Related Research Articles
Micropsia is a condition affecting human visual perception in which objects are perceived to be smaller than they actually are. Micropsia can be caused by optical factors, by distortion of images in the eye, by changes in the brain, and from psychological factors. Dissociative phenomena are linked with micropsia, which may be the result of brain-lateralization disturbance.
Alice in Wonderland syndrome (AIWS), also known as Todd's syndrome or dysmetropsia, is a neurological disorder that distorts perception. People with this syndrome may experience distortions in their visual perception of objects, such as appearing smaller (micropsia) or larger (macropsia), or appearing to be closer (pelopsia) or farther (teleopsia) than they are. Distortion may also occur for senses other than vision.
Macropsia is a neurological condition affecting human visual perception, in which objects within an affected section of the visual field appear larger than normal, causing the person to feel smaller than they actually are. Macropsia, along with its opposite condition, micropsia, can be categorized under dysmetropsia. Macropsia is related to other conditions dealing with visual perception, such as aniseikonia and Alice in Wonderland Syndrome. Macropsia has a wide range of causes, from prescription and illicit drugs, to migraines and (rarely) complex partial epilepsy, and to different retinal conditions, such as epiretinal membrane. Physiologically, retinal macropsia results from the compression of cones in the eye. It is the compression of receptor distribution that results in greater stimulation and thus a larger perceived image of an object.
The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ob, 'behind', and caput, 'head'.
A headache is often present in patients with epilepsy. If the headache occurs in the vicinity of a seizure, it is defined as peri-ictal headache, which can occur either before (pre-ictal) or after (post-ictal) the seizure, to which the term ictal refers. An ictal headache itself may or may not be an epileptic manifestation. In the first case it is defined as ictal epileptic headache or simply epileptic headache. It is a real painful seizure, that can remain isolated or be followed by other manifestations of the seizure. On the other hand, the ictal non-epileptic headache is a headache that occurs during a seizure but it is not due to an epileptic mechanism. When the headache does not occur in the vicinity of a seizure it is defined as inter-ictal headache. In this case it is a disorder autonomous from epilepsy, that is a comorbidity.
Palinopsia is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis; it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia.
An aura is a perceptual disturbance experienced by some with epilepsy or migraine. An epileptic aura is actually a minor seizure.
Frontal lobe epilepsy (FLE) is a neurological disorder that is characterized by brief, recurring seizures arising in the frontal lobes of the brain, that often occur during sleep. It is the second most common type of epilepsy after temporal lobe epilepsy (TLE), and is related to the temporal form in that both forms are characterized by partial (focal) seizures.
Foix–Chavany–Marie syndrome (FCMS), also known as bilateral opercular syndrome, is a neuropathological disorder characterized by paralysis of the facial, tongue, pharynx, and masticatory muscles of the mouth that aid in chewing. The disorder is primarily caused by thrombotic and embolic strokes, which cause a deficiency of oxygen in the brain. As a result, bilateral lesions may form in the junctions between the frontal lobe and temporal lobe, the parietal lobe and cortical lobe, or the subcortical region of the brain. FCMS may also arise from defects existing at birth that may be inherited or nonhereditary. Symptoms of FCMS can be present in a person of any age and it is diagnosed using automatic-voluntary dissociation assessment, psycholinguistic testing, neuropsychological testing, and brain scanning. Treatment for FCMS depends on the onset, as well as on the severity of symptoms, and it involves a multidisciplinary approach.
Abdominal epilepsy is a rare condition most frequently found in children, consisting of gastrointestinal disturbances caused by epileptiform seizure activity. Though a few cases of it have been reported in adults too. It has been described as a type of temporal lobe epilepsy. Responsiveness to anticonvulsants can aid in the diagnosis. Distinguishing features of abdominal epilepsy include (1) Abnormal laboratory, radiographic, and endoscopic findings revealing paroxysmal GI manifestations of unknown origin (2) CNS symptoms (3) Abnormal EEG. Most published medical literature dealing with abdominal epilepsy is in the form of individual case reports. A 2005 review article found a total of 36 cases described in the medical literature.
Ohtahara syndrome (OS), also known as Early Infantile Developmental & Epileptic Encephalopathy (EIDEE) is a progressive epileptic encephalopathy. The syndrome is outwardly characterized by tonic spasms and partial seizures within the first few months of life, and receives its more elaborate name from the pattern of burst activity on an electroencephalogram (EEG). It is an extremely debilitating progressive neurological disorder, involving intractable seizures and severe intellectual disabilities. No single cause has been identified, although in many cases structural brain damage is present.
Transient epileptic amnesia (TEA) is a rare but probably underdiagnosed neurological condition which manifests as relatively brief and generally recurring episodes of amnesia caused by underlying temporal lobe epilepsy. Though descriptions of the condition are based on fewer than 100 cases published in the medical literature, and the largest single study to date included 50 people with TEA, TEA offers considerable theoretical significance as competing theories of human memory attempt to reconcile its implications.
Panayiotopoulos syndrome is a common idiopathic childhood-related seizure disorder that occurs exclusively in otherwise normal children and manifests mainly with autonomic epileptic seizures and autonomic status epilepticus. An expert consensus has defined Panayiotopoulos syndrome as "a benign age-related focal seizure disorder occurring in early and mid-childhood. It is characterized by seizures, often prolonged, with predominantly autonomic symptoms, and by an EEG [electroencephalogram] that shows shifting and/or multiple foci, often with occipital predominance."
Lesions in the visual pathway affect vision most often by creating deficits or negative phenomena, such as blindness, visual field deficits or scotomas, decreased visual acuity and color blindness. On occasion, they may also create false visual images, called positive visual phenomena. These images can be a result of distortion of incoming sensory information leading to an incorrect perception of a real image called an illusion. When the visual system produces images which are not based on sensory input, they can be referred to as hallucinations. The visual phenomena may last from brief moments to several hours, but they also can be permanent. They are generally associated with other symptoms but occasionally are isolated. Conditions causing these phenomena include disruptions in the visual input along the pathways lesions in the extracortical visual system, migraines, seizures, toxic-metabolic encephalopathy, psychiatric conditions and sleep apnea, among others. The mechanisms underlying positive visual phenomena are not yet well understood. Possible mechanisms may be: 1) defect in the sensory input causing compensatory upregulation of the visual cortex, 2) faulty visual processing in which inputs are normal but lesions result in an inappropriate pattern of cortical excitation, 3)variants of normal visual processing. Of all forms of hallucination, visual hallucinations are the least likely to be associated with psychiatric disorders. For example most patients with visual hallucinations do not have schizophrenia and most patients with schizophrenia do not have visual hallucinations.
Migralepsy is a rare condition in which a migraine is followed, within an hour period, by an epileptic seizure. Because of the similarities in signs, symptoms, and treatments of both conditions, such as the neurological basis, the psychological issues, and the autonomic distress that is created from them, they individually increase the likelihood of causing the other. However, also because of the sameness, they are often misdiagnosed for each other, as migralepsy rarely occurs.
Abdominal aura, also known as visceral aura and epigastric aura, is a type of somatosensory aura that typically manifests as abdominal discomfort in the form of nausea, malaise, hunger, or pain. Abdominal aura is typically associated with epilepsy, especially temporal lobe epilepsy, and it can also be used in the context of migraine. The term is used to distinguish it from other types of somatosensory aura, notably visual disturbances and paraesthesia. The abdominal aura can be classified as a somatic hallucination. Pathophysiologically, the abdominal aura is associated with aberrant neuronal discharges in sensory cortical areas representing the abdominal viscera.
Vertiginous epilepsy is infrequently the first symptom of a seizure, characterized by a feeling of vertigo. When it occurs, there is a sensation of rotation or movement that lasts for a few seconds before full seizure activity. While the specific causes of this disease are speculative there are several methods for diagnosis, the most important being the patient's recall of episodes. Most times, those diagnosed with vertiginous seizures are left to self-manage their symptoms or are able to use anti-epileptic medication to dampen the severity of their symptoms.
Idiopathic childhood occipital epilepsy of Gastaut (ICOE-G) is a pure but rare form of idiopathic occipital epilepsy that affects otherwise normal children and adolescents. It is classified amongst benign idiopathic childhood focal epilepsies such as rolandic epilepsy and Panayiotopoulos syndrome.
An epilepsy syndrome is defined as "a characteristic cluster of clinical and Electroencephalography (EEG) features, often supported by specific etiological findings ."
Cerebral diplopia or polyopia describes seeing two or more images arranged in ordered rows, columns, or diagonals after fixation on a stimulus. The polyopic images occur monocular bilaterally and binocularly, differentiating it from ocular diplopia or polyopia. The number of duplicated images can range from one to hundreds. Some patients report difficulty in distinguishing the replicated images from the real images, while others report that the false images differ in size, intensity, or color. Cerebral polyopia is sometimes confused with palinopsia, in which multiple images appear while watching an object. However, in cerebral polyopia, the duplicated images are of a stationary object which are perceived even after the object is removed from the visual field. Movement of the original object causes all of the duplicated images to move, or the polyopic images disappear during motion. In palinoptic polyopia, movement causes each polyopic image to leave an image in its wake, creating hundreds of persistent images (entomopia).
References
↑ MacPhee, Stephen J., ed. (2010). "7". Pathophysiology of disease: an introduction to clinical medicine. Lange medical book (6thed.). New York: McGraw-Hill Medical. ISBN978-0-07-162167-0.
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