Seizures and Epilepsy in Horses: Types, Management & Prognosis

Seizures, while relatively rare in equines compared to dogs and humans, pose a significant challenge for horse owners and veterinarians. These neurological episodes, characterized by abnormal electrical activity in the brain, can take various forms depending on severity and their location in the brain. ^[1]

During a seizure, a horse may experience loss of consciousness, collapse, muscle twitching, uncontrolled movements, and sometimes vocalizations or loss of bladder control, among other signs.

The complexity of seizure disorders in horses makes diagnosis and treatment complicated in some cases. ^[2] Diagnosis involves neurological exams and tests to differentiate factors causing the seizures.

Epilepsy in horses is a neurological disorder characterized by recurrent seizures. While all horses with epilepsy experience seizures, not all seizures in horses are due to epilepsy. ^[3]

First occurrence of seizures or episodes lasting more than one minute are medical emergencies. If you suspect your horse is having a seizure, contact a veterinarian immediately.

Seizures in Horses

Seizures are a neurological symptom that result from abnormal electrical activity in the brain. The specific symptoms associated with seizures vary depending on the location and severity of the electrical dysfunction in the brain. ^[1]

Seizures may appear as any or a combination of: ^[1][2][3]

• Stiffness
• Collapse
• Convulsions
• Loss of consciousness
• Loss of bladder or rectal control

Types of Seizures

Seizures in horses can be broadly categorized into three main types:

• Generalized
• Partial (or focal)
• Status epilepticus

It’s helpful for horse owners and care takers to familiarize themselves with the different types of seizures so they are prepared if one of their equines is ever suspected of seizing.

Generalized Seizure (Grand Mal)

Generalized seizures involve the entire brain from the onset, affecting both hemispheres simultaneously. These seizures typically result in loss of consciousness and can be divided into several subtypes, with the most well-known being tonic-clonic (formerly referred to as grand mal) seizures. ^[1]

Tonic-clonic seizures develop in a series of phases: ^[2][4]

• Prodromal: before the electrical dysfunction takes hold, affected horses may become anxious.
• Pre-ictal: anxiety or other feelings developing in the prodromal phase sometimes progress into mild, early signs of seizure activity. In some cases, before a seizure begins, horses may exhibit specific behaviors known as an “aura.” It’s important to note that not all seizures are preceded by an aura or obvious changes in behavior.
• Ictal: characterized by the physical and neurological manifestations of the seizure. During the ictal phase, affected horses may have sudden stiffening of muscles (tonic symptom) and rhythmic jerking movements (clonic symptom).
• Post-ictal: once the seizure is over, affected horses may recover quickly while others need hours or days to return to normal energy levels.

Generalized seizures are usually more dramatic and easier to identify compared to partial seizures. Horses having a generalized seizure may: ^[2]

• Collapse
• Lose consciousness
• Drool excessively
• Vocalize
• Lose control of the bladder or rectum

Partial Seizures

Partial seizures, also known as focal seizures, originate in a specific area of the brain and affect only part of the body.

These seizures can present with localized symptoms such as: ^[2][3]

• Muscle twitching
• Abnormal movements
• Behaviors limited to one limb or side of the body
• Compulsive running or circling
• Self-harming tendencies

Horses experiencing partial seizures may remain conscious or have altered awareness, depending on the seizure’s complexity. Simple focal seizures involve localized symptoms without loss of consciousness, while complex focal seizures may impair awareness.

Status epilepticus

Status epilepticus is a very rare and serious condition in horses. Affected horses experience prolonged seizures lasting more than five minutes, or a series of seizures without regaining full consciousness between them. ^[2]

Due to the energy lost during the seizure, the nervous system cannot return to normal. The severity of these seizures can impede normal biological functions, including breathing, which can be fatal. ^[5]

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Causes of Seizures in Horses

Seizures in horses can be triggered by a variety of underlying factors. The most common causes of seizures in horses include: ^[1][2][3]

• Head injury
• Infections (viral encephalitis, bacterial meningitis, parasites)
• Metabolic disorders (electrolyte imbalances, hypoglycemia)
• Toxins (ingestion of toxic plants, chemical poisoning, mycotoxins)
• Neurological conditions (brain tumors)
• Genetic disorders
• Oxygen deprivation during birth (hypoxia)

Epilepsy

Epilepsy is a chronic neurological disorder characterized by recurrent seizures. It can be challenging to diagnose and manage due to the variety of potential causes, including genetic factors, brain injuries, and metabolic disorders.

Equine epilepsy is divided into five categories: ^[1][3]

• Primary: also referred to as idiopathic epilepsy, these seizures are presumed to have a genetic origin and typically occur sporadically without an associated structural abnormality in the brain. Despite extensive testing, no underlying structural abnormalities or systemic diseases are found to explain the seizure activity.
• Reactive: occurs when the brain responds to a temporary systemic issue or disturbance in the body. These seizures are typically triggered by conditions such as electrolyte imbalances (e.g., low sodium or calcium levels), liver disease, kidney failure, severe infections, or toxin exposure. Once the underlying systemic issue is addressed and corrected, the seizures usually cease.
• Secondary: occurs when seizures are a result of an underlying structural or systemic disorder affecting the brain. This can include conditions such as inflammatory diseases, tumors, vascular events, or head trauma.
• Symptomatic: occurs when seizures are a result of an underlying structural or systemic disorder affecting the brain. Common causes of symptomatic epilepsy in horses include brain tumors, vascular events, meningitis, and head trauma.
• Cryptogenic: involves recurrent seizures despite normal neurodiagnostic test results, indicating hidden brain abnormalities not detectable with current methods.

Seizures in Foals

Foals have a lower seizure threshold, making them more prone to seizures than adult horses. This susceptibility is due to the immaturity of their nervous system and brain development. ^[6]

Seizures in foals, although rare, can stem from various underlying causes. One primary factor contributing to seizures in foals is infections, including viral, bacterial, or parasitic pathogens. These infections can affect the brain directly, causing inflammation and disrupting normal neurological function. ^[7]

Some causes of seizures in foals include: ^{[6][8][9][10][11]}

• Neonatal Encephalopathy: also referred to as dummy foal syndrome, this condition describes abnormal brain function in newborn foals. It presents with a range of neurological symptoms such as disorientation, lethargy, weakness, and seizures.
• Hypoglycemia: an abnormally low level of glucose (blood sugar) in the bloodstream of newborn horses. This condition can occur due to various factors such as inadequate milk intake, limited energy reserves, or underlying metabolic disorders. Hypoglycemia can lead to neurological symptoms, weakness, seizures, and other complications if not promptly addressed.
• Hypoxia: a condition where there is a deficiency of oxygen reaching the body tissues. This can occur during birth if the foal experiences difficulty in the birthing process, leading to a decreased oxygen supply to the brain and other organs. Hypoxia can result in neurological symptoms and respiratory distress.

Juvenile idiopathic epilepsy (JIE)

Juvenile idiopathic epilepsy (JIE) is a neurological disorder in foals characterized by recurrent seizures that usually start within the first few days or months of life, often before six months of age. Between seizures, foals do not demonstrate any other signs of illness. ^[7][12]

The cause of JIE is unknown, although it is believed to have a genetic basis, particularly in Arabian horses. Clinical signs can range from mild to severe. During a seizure, foals may experience minor twitching and decreased blinking, or they may lose consciousness and collapse. ^[13]

To manage seizures, treatment may be administered at the discretion of a veterinarian. Short-term anticonvulsants like benzodiazepines and long-term phenobarbital, which slows nervous system activity, may be used. After a year of age, foals typically stop experiencing seizures and medications can be tapered off. ^[12]

Diagnosis

The first step in diagnosing the underlying cause of equine seizures is taking a detailed history and physical examination. Any case with sudden, involuntary neurological events is considered to have potential seizure activity until proven otherwise. ^[1]

Veterinarians presented with confirmed or suspected seizures need to rule out other symptoms and conditions with similar presentation including:

• Colic
• Muscle pain
• Hyperkalemic periodic paralysis (HYPP)
• Syncope (fainting)
• Narcolepsy/cataplexy

Neurological Examination

When presented with a case of equine seizures, veterinarians usually perform a complete neurological exam to check for other signs of nervous system dysfunction. During this exam, the veterinarian evaluates the horse’s cranial nerve function by assessing: ^[3][14]

• Vision
• Hearing
• Facial muscle movements
• Swallowing

The horse’s gait and posture are also observed while walking, trotting, turning, and navigating obstacles to detect any dysfunction in coordination and balance. Neck and back flexion tests identify stiffness or pain, while proprioception (i.e. the horse’s awareness of where their limbs are relative to each other) is checked by placing limbs in unusual positions and observing how the horse returns to the normal posture.

Reflexes are tested by tapping the knees and hocks, and by examining the tail and anal tone. Pain response is assessed by palpating various body areas. These evaluations help pinpoint neurological dysfunction and guide further diagnostic tests and treatments.

Electroencephalography (EEG)

Electroencephalography (EEG) is a diagnostic test that measures electrical brain activity, which aids in detecting abnormal patterns that point to seizures or epilepsy in horses. It helps distinguish between partial and generalized seizures and can be used to monitor efficacy of treatment. ^[1][15]

During the procedure, electrodes are placed on the horse’s scalp to record brain signals, which are then analyzed by a veterinarian to assess brain function and identify abnormalities.

Other Diagnostics

By conducting additional diagnostic tests, veterinarians can evaluate the overall health of the horse, identify potential factors contributing to seizures, such as systemic disorders or metabolic imbalances, and develop suitable treatment strategies to manage seizure triggers.

Generally, other testing related to seizures is performed on bloodwork, and specific tests may include: ^[2][5][16]

• Complete Blood Count (CBC): checks for anemia, infections, or inflammation, providing insights into overall health
• Serum Biochemistry Analysis: assesses electrolyte levels, liver and kidney function, and glucose levels to detect metabolic disorders
• Arterial Blood Gas Analysis: measures oxygen, carbon dioxide, and pH levels to assess respiratory and metabolic status
• Serum Ammonia Concentration: identifies liver dysfunction and ammonia buildup, which can lead to neurological symptoms like seizures

If there is no underlying cause detected, the source of seizures likely lies within the brain itself. Diagnostic imaging, such as X-rays, of the skull and cerebrospinal fluid (CSF) analysis (i.e. “spinal tap”) may be recommended.

CSF analysis may include testing for viral infections that cause inflammation of the brain, such as equine protozoal myeloencephalitis (EPM). ^[2][3][5]

Treatment

Treatment for seizures, particularly epilepsy, in horses typically aims at managing and reducing seizure frequency while addressing underlying causes, if any are identified.

Anticonvulsant medications are commonly prescribed to control seizures and stabilize brain activity. Benzodiazepines, such as diazepam or midazolam, may be administered for acute seizure management or as rescue therapy during prolonged seizures.

For seizures induced by toxins, diazepam is often used to manage and control the seizures effectively. ^[1][2][17]

Long-term Management

Long-term anticonvulsant therapy is rare in horses. If horses have frequent seizures, such as more than one every two months, clusters several times a year, or multiple seizures within a few days, long-term management may be necessary.

For ongoing seizure activity, medications like phenobarbital can regulate neuronal excitability and prevent seizure episodes. Alternatives such as potassium bromide, phenytoin, or a mixture of chloral hydrate and magnesium sulfate may also be considered by the veterinarian. ^[2][12][17]

After successfully managing seizures in horses for a fixed period, most veterinarians recommend gradually weaning off maintenance medication to evaluate if ongoing treatment is still necessary. This allows veterinarians to assess the horse’s response and determine whether seizures remain controlled without medication.

Prevention

While it may not be possible to completely prevent seizures, especially in cases of idiopathic epilepsy, the following strategies can help reduce their frequency and severity: ^[2]

• Veterinary Care: ensure regular veterinary check-ups are scheduled to monitor the horse’s health and adjust treatments as needed. Keep vaccinations and deworming schedules up to date to prevent infections that may trigger seizures. Promptly address any underlying health issues to prevent conditions associated with secondary seizures.
• Medication Management: administer prescribed anticonvulsant medications consistently as directed by the veterinarian. Monitor for side effects and efficacy, and communicate any concerns to the prescribing veterinarian.
• Routine Monitoring: observe the horse for early signs of distress or unusual behavior that might precede a seizure. Keep a seizure log to track the frequency, duration, and potential triggers of seizures to help manage and prevent future episodes.
• Avoid Toxins: ensure the horse’s environment is free from toxic plants, chemicals, and other substances that could induce seizures. Be cautious with medications and supplements, using only those prescribed or approved by a veterinarian. Always inform your veterinarian of all medications and supplements your horse is currently on before starting new medications.

Prognosis

For foals facing seizures, the outlook is usually positive, as they commonly outgrow the condition within weeks or months. With proper care and management, most affected foals fully recover and lead healthy lives.

In adult horses, the prognosis is also generally favorable. Although partial seizures may advance to full seizures in some instances, many adult horses with seizures respond well to treatment and can maintain relatively normal lives with appropriate management. ^[2]

Seizures in horses can pose significant risks, especially during activities such as riding or exercise. These episodes can be violent and unpredictable, potentially endangering both the horse and anyone nearby.

It’s often advised not to ride horses with epilepsy until they’ve been seizure-free, without anticonvulsant therapy, for at least six months. This ensures careful monitoring for stability and lowers the risk of seizures during physical activity, which could be harmful. ^[2]

Summary

Seizures in horses, though rare compared to dogs and humans, pose significant challenges for horse owners and veterinarians.

• Epilepsy refers to recurrent, unprovoked seizures and can be primary (idiopathic), reactive, or secondary
• Causes of seizures in horses include head injury, infections, metabolic disorders, toxins, neurological conditions, genetic disorders, and birth-related issues
• Diagnosing seizures involves neurological exams, EEG, and additional tests like CBC, serum biochemistry, arterial blood gas analysis, and serum ammonia concentration
• Treatment includes anticonvulsant medications like diazepam and phenobarbital