Encephalon
The equine brain weighs approximately 600 g in adult horses (roughly 0.1% of body mass). It is gyrencephalic with a moderately convoluted cerebral cortex. The cerebellum is relatively large, reflecting the demands of balance, coordination, and proprioception in a large, fast quadruped. The brainstem contains nuclei for many cranial nerves and controls vital functions (respiration, cardiovascular regulation). The blood-brain barrier limits many drugs, complicating treatment of CNS infections. The spinal cord continues caudally through the vertebral canal. Clinically, a full neurologic examination evaluates mentation, cranial nerves, gait (Mayhew scale 0–5), and postural reactions. CSF analysis (atlanto-occipital or lumbosacral) and advanced imaging (MRI, CT) are used for diagnosis. Core vaccinations against EEE, WEE, WNV, and tetanus remain essential preventive measures.
Mayhew scale grades ataxia. CSF and advanced imaging are key diagnostics. Differential includes EPM (equine protozoal myeloencephalitis), cervical vertebral stenotic myelopathy, trauma, and infectious encephalitides.
## Overview Equine protozoal myeloencephalitis (EPM) is a neurologic disease caused by infection of the central nervous system with Sarcocystis neurona (most cases) or Neospora hughesi. It produces h
## Overview West Nile virus encephalitis is mosquito-borne inflammation of the brain and spinal cord. Many infected horses show no signs. Those that do develop fever, muscle tremors (especially of th
## Overview Eastern equine encephalitis (EEE) and Western equine encephalitis (WEE) are mosquito-borne viral diseases that cause severe neurologic illness. EEE has a mortality rate approaching 90 per
Wobbler syndrome, also known as cervical vertebral stenotic myelopathy, is a neurologic condition caused by compression of the spinal cord in the neck. It leads to progressive incoordination (ataxia),
## Overview Head trauma in horses ranges from concussion to skull fracture and brain injury. Signs include altered mentation, unequal pupils, nystagmus, vestibular signs, bleeding from ears or nose,
## Overview Equine herpesvirus-1 myeloencephalopathy (EHM) is the neurologic form of equine herpesvirus-1 infection. Neuropathogenic strains cause vasculitis and ischemic damage to the spinal cord. T
Sudden incoordination, circling, head tilt, seizures, or changes in mentation are emergencies. Keep core vaccines current. Do not attempt to force a neurologic horse to move if it is unsafe.
## Overview Equine protozoal myeloencephalitis (EPM) is a neurologic disease caused by infection of the central nervous system with Sarcocystis neurona (most cases) or Neospora hughesi. It produces highly variable signs, most often asymmetric ataxia and muscle atrophy. It occurs in the Americas. ## Causes Ingestion of sporocysts shed by opossums (for Sarcocystis neurona), followed by aberrant migration into the nervous system. ## Diagnosis Neurologic examination plus serum and cerebrospinal fluid antibody testing showing intrathecal antibody production. Other causes of ataxia are excluded. ## Treatment FDA-approved antiprotozoal drugs (ponazuril, diclazuril, or sulfadiazine/pyrimethamine) for 28 days or longer, plus supportive care and anti-inflammatories. ## Recovery and Prognosis Approximately 60 to 70 percent of treated horses improve. Complete recovery is less common. Relapse can occur. ## Prevention Reduce opossum access to feed. No fully effective vaccine is available. Signs include: asymmetric ataxia (often worse behind); muscle atrophy; stumbling; cranial nerve signs in some cases; can be acute or progressive
## Overview West Nile virus encephalitis is mosquito-borne inflammation of the brain and spinal cord. Many infected horses show no signs. Those that do develop fever, muscle tremors (especially of the face and muzzle), stumbling, hypersensitivity to touch and sound, ataxia, and in severe cases recumbency. There is no specific cure. Supportive care is given while the horse fights the infection. Vaccination and mosquito control have reduced cases. ## Causes West Nile virus transmitted by mosquitoes. ## Diagnosis Clinical signs and blood or cerebrospinal fluid testing for antibodies. ## Treatment Supportive care, anti-inflammatories, and nursing. Mortality in clinical cases is significant. ## Recovery and Prognosis Variable. Mild cases often recover. Recumbent horses have a poorer outlook. Some have residual deficits. ## Prevention Annual vaccination and mosquito control. Signs include: fever; muscle tremors; stumbling; hypersensitivity to touch and sound; recumbency in severe cases; facial fasciculations; ataxia; hind-limb weakness
## Overview Eastern equine encephalitis (EEE) and Western equine encephalitis (WEE) are mosquito-borne viral diseases that cause severe neurologic illness. EEE has a mortality rate approaching 90 percent; WEE is less deadly (approximately 30 to 50 percent). Both are core vaccines recommended by the American Association of Equine Practitioners. ## Causes Alphaviruses transmitted by mosquitoes from bird reservoirs. ## Diagnosis Clinical signs of fever and rapidly progressive neurologic disease plus serology or polymerase chain reaction testing. ## Treatment Supportive care only. No specific antiviral therapy exists. Survival is uncommon with EEE. ## Recovery and Prognosis Poor for EEE. Survivors of either disease may have residual neurologic deficits. ## Prevention Annual vaccination and mosquito control. Signs include: high fever; depression; circling; head pressing; blindness; seizures; rapid progression to death (especially EEE)
Wobbler syndrome, also known as cervical vertebral stenotic myelopathy, is a neurologic condition caused by compression of the spinal cord in the neck. It leads to progressive incoordination (ataxia), primarily in the hind limbs. There are two main forms: Type I (dynamic compression in young horses) and Type II (static compression in older horses due to osteoarthritis). ## What it is In Type I wobbler syndrome, developmental abnormalities of the cervical vertebrae cause narrowing of the vertebral canal and dynamic compression of the spinal cord during neck movement. It typically affects horses between 1 and 4 years of age, most commonly at C3 to C5. Type II wobbler involves static compression from osteoarthritic enlargement of the articular facets, usually affecting older horses at C5 to C7. Both forms result in damage to the spinal cord, leading to proprioceptive deficits and ataxia that is usually worse in the hind limbs. ## Signs and symptoms - Progressive hindlimb incoordination and ataxia - Wide-based stance and stumbling, especially when turning or going downhill - Toe dragging and difficulty backing - Neck stiffness or pain in some cases - In severe cases, weakness or falling - Symmetric or slightly asymmetric ataxia that is worse in the hind limbs than forelimbs - Positive cervical flexion test in many cases ## Causes and risk factors Type I wobbler is developmental and linked to rapid growth, genetic factors, and nutritional imbalances (especially copper deficiency or excess protein/calcium in young horses). Type II is associated with chronic wear and osteoarthritis of the cervical facet joints. Risk factors include large body size, rapid growth rates in young horses, and conformational issues that place abnormal stress on the neck. ## How it is diagnosed Diagnosis is based on clinical neurologic examination and confirmed with radiographs and myelography or MRI. Standing or recumbent radiographs can show vertebral canal narrowing or facet joint changes. Myelography or MRI provides the most accurate assessment of spinal cord compression. A neurologic grading system helps quantify the severity of ataxia. ## Treatment and management Treatment depends on the type, severity, and age of the horse. Conservative management includes stall rest, anti-inflammatory medication, and controlled exercise. For young horses with Type I, dietary management and restricted growth may help. Surgical options (ventral interbody fusion or dorsal laminectomy) are available for selected cases and can improve neurologic function in many horses. Prognosis varies widely depending on the severity and duration of compression before treatment. ## When to call the vet Contact your veterinarian promptly if your horse shows incoordination, stumbling, or difficulty backing or turning. Early diagnosis improves the chance of successful management or surgical intervention. ## Prevention For Type I wobbler in young horses, prevention focuses on balanced nutrition (avoiding excessive protein and calcium while ensuring adequate copper and other minerals) and avoiding overly rapid growth rates. Regular monitoring of at-risk young horses can help with early detection. ## Frequently asked questions **Can a horse with wobbler syndrome be ridden?** Many horses with mild to moderate signs can be ridden carefully after treatment, but those with severe ataxia are usually retired for safety reasons. **Is surgery always successful for wobbler syndrome?** Surgical success rates are good in appropriately selected cases, but results vary depending on the severity and chronicity of spinal cord damage. **Is wobbler syndrome hereditary?** There is a genetic component, especially in Type I. Breeding horses with wobbler syndrome or from lines with high incidence is generally discouraged. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Progressive hindlimb incoordination and ataxia; wide-based stance and stumbling, especially when turning or going downhill; toe dragging and difficulty backing; neck stiffness or pain in some cases; in severe cases, weakness or falling; symmetric or slightly asymmetric ataxia worse in hind limbs; positive cervical flexion test in many cases
## Overview Head trauma in horses ranges from concussion to skull fracture and brain injury. Signs include altered mentation, unequal pupils, nystagmus, vestibular signs, bleeding from ears or nose, and seizures. Basilar skull fractures are particularly serious. ## Causes Falls, rearing over backward, kicks, or collisions. ## Diagnosis Neurologic examination and radiographs or computed tomography of the skull. Cerebrospinal fluid analysis when indicated. ## Treatment Stabilize, control seizures and brain swelling, and provide supportive nursing. Surgical decompression is rarely feasible. Prognosis depends on the severity of brain injury. ## Recovery and Prognosis Variable. Mild concussion often recovers. Severe brain injury or skull fracture carries a guarded to poor outlook. ## Prevention Safe handling and environments that reduce rearing and falling risks. Signs include: altered consciousness; unequal pupils; head tilt; bleeding from ears or nose; seizures; nystagmus; recumbency
## Overview Equine herpesvirus-1 myeloencephalopathy (EHM) is the neurologic form of equine herpesvirus-1 infection. Neuropathogenic strains cause vasculitis and ischemic damage to the spinal cord. Typical signs are fever followed by acute hind-limb ataxia, urinary incontinence, and potentially rapid progression to recumbency. Outbreaks occur. ## Causes Neuropathogenic equine herpesvirus-1 (often associated with a specific DNA polymerase mutation). ## Diagnosis Clinical signs plus polymerase chain reaction testing of nasal swabs and blood, and cerebrospinal fluid analysis. ## Treatment Supportive care, anti-inflammatories, and nursing for recumbent horses. Antiviral drugs are sometimes used. Isolation is critical to prevent spread. ## Recovery and Prognosis Guarded. Horses that remain standing have a better chance. Recumbent horses have high mortality. ## Prevention Vaccination reduces respiratory disease and abortion but does not fully prevent neurologic disease. Biosecurity during outbreaks is essential. Signs include: fever followed by acute hind-limb ataxia and weakness; urinary incontinence; perineal hypalgesia; may progress to recumbency
Mayhew scale grades ataxia. CSF and advanced imaging are key diagnostics. Differential includes EPM (equine protozoal myeloencephalitis), cervical vertebral stenotic myelopathy, trauma, and infectious encephalitides.
Sudden incoordination, circling, head tilt, seizures, or changes in mentation are emergencies. Keep core vaccines current. Do not attempt to force a neurologic horse to move if it is unsafe.
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