Medical Neurology

A seizure is a sudden, uncontrolled electrical brain disturbance that causes behavioral changes, bodily movements, and unconsciousness. To treat a pet’s condition appropriately, a veterinary neurologist must first determine the seizure’s underlying cause, which may include primary epilepsy, metabolic disease, brain tumor, or brain infection or inflammation.

Vestibular disease or poor balance is a sign of brain or nerve disease and can happen to any pet. The good news is that many of the causes of vestibular disease are very responsive to treatment; however, some causes are life-threatening. Therefore, if your pet has vestibular disease, achieving a rapid diagnosis can be very important. This information will help you understand what may be the cause of your pet’s balance problem.

Indications of Nerve (Peripheral) Disease

• Horizontal or rotary nystagmus (eye twitching)
• Fast phase of nystagmus is opposite the direction of the head tilt
• Nystagmus at a rate of 1 beat per second
• Pets are able to walk & are bright & responsive
• Vomiting can occur in the first few hours
• Balance and nystagmus improve in 1-2 days and head tilt improves more slowly

Indications of Brain (Central) Disease

• Vertical nystagmus or fast phase towards head tilt
• Slow rate of nystagmus or only seen when the head is in certain positions
• Inability to walk or high stepping when walking
• Dullness, glassy-eyed appearance, confusion, eliminating in the house.
• Seizure, blindness, head turn, different pupil sizes

Pets with vestibular disease walk as if they are drunk because they side step, lean, or stumble to one side. Poor balance is called vestibular disease because the receptors that sense movement and head position are located in the vestibule of the inner ear. Information from these receptors runs along the vestibular nerve into the brain. The brain then processes this information to make adjustments in head and body position. The cause of vestibular disease can be from a problem in the brain or a problem in the nerve. Disease located in the brain is often called central while disease of the nerve is called peripheral. Nerve or peripheral disease is generally self-limiting or easily treated; however, disease of the brain can be life threatening, especially when left untreated. A careful examination will indicate the location and therefore the seriousness of the disease.

Central vs. Peripheral – A Critical Distinction

In addition to controlling head and body position and therefore balance, the brain also controls level of awareness, strength, walking, pupil size, breathing and the heart beat. Some of the diseases that affect the brainstem can cause difficulty walking, coma and even death. These diseases can be rapidly progressive; therefore, distinguishing central from peripheral disease early on can be very important.

Causes for Vestibular Disease

The most common diseases of the peripheral nerve are bacterial infection and inflammation that cross from the middle ear into inner ear, low thyroid and a process called idiopathic peripheral vestibular disease. The most common diseases of the brainstem are granulomatous meningoencephalomyelitis (GME), tumor, stroke, low thyroid and infection.

Common Testing for Pets with Poor Balance

• Blood evaluation (Chemistry, Complete Blood Cell Count, thyroid levels, tests for infection)
• Blood pressure
• MRI
• Cerebral spinal fluid (CSF) analysis
• Antibiotic and/or steroid trial
• Brainstem auditory evoked response (BAER)

MRI is invaluable as it is the best imaging test for the brain, middle and inner ear. Which test(s) BVNS would choose in any particular case often depends on age, breed, progression and clinical impression.

When to See a Neurologist

Many veterinarians offer referral to get the best opinion about where the disease is located. Once this is determined, the most appropriate test may become obvious allowing for more accurate and rapid treatment. Another common reason for referral is the suspicion that the disease may be in the brain and therefore, life threatening. Timely advanced testing followed by specific therapy, can be the difference between life and death.

Common Diseases Resulting in Poor Balance

Encephalitis

Encephalitis means that there is inflammation of the brain – it does not imply that the cause of the inflammation is known. Encephalitis can be infectious or non-infectious. Encephalitis is more common in small dogs, younger than 8 years of age, but any dog or cat can get the disease. The diagnosis is often made using MRI, spinal fluid analysis and infectious disease tests. A rapid, specific diagnosis provides for the best treatment and outcome of this life-threatening disease.

Granulomatous Meningoencphalomyelitis (GME )

GME is inflammation (more white blood cells than normal) in the brain, meninges or spinal cord in the absence of infection or a brain tumor. GME is theorized to be an immune disease where the immune system attacks the nervous system. GME often involves the balance center of the brain and many patients have several of the signs of central disease listed on the front. MRI and CSF analysis and a high index of suspicion are often required to make a diagnosis of GME. If the patient is not rapidly deteriorating, infectious disease tests and an antibiotic trial are ideally done to rule-out an infectious cause. GME can be rapidly progressive and about 10% of pets do not survive their initial manifestation of the disease. There are many new drugs for GME which are allowing more dogs to do well. The current 1 year survival rate for this disease is about 70% with many patients living longer, normal lives while on medication. A rapid diagnosis improves the odds of being able to survive the initial symptoms and go on to live well.

Any breed of dog and cats can be affected with a brain tumor. Older dogs or cats and certain breeds like the Golden retriever, Boxer, and larger breed dogs in general are at higher risk for brain tumors.

Cause

The cause of brain tumor or cancer in general is not known. However, because certain breeds are at higher risk, there must be a genetic and environmental component.

Symptoms

Brain tumors can affect any part of the brain and therefore can cause a variety of problems. Symptoms include seizure, confusion, sedation, poor balance, weakness and with progression stupor, coma and death. In dogs, seizure can be the only sign of a brain tumor. Pain can be associated with brain tumor by affecting the pain processing portion of the brain or spinal cord or inflaming or stretching the lining of the brain, the meninges.

Diagnostics

The diagnosis of a brain tumor is made by imaging a mass next to or within the axis of the brain and ruling-out the possibility that the mass is from infection. Often MRI characteristics alone are thought to be sufficient to diagnose a brain tumor. Ruling out infection is often done by performing infectious tests on the blood or/and spinal fluid and by performing an analysis of the cerebrospinal fluid (CSF).

Treatment

Treatment to reduce or eliminate the brain tumor can include surgery, radiation, and/or chemotherapy. Treatment to control the signs of a tumor can include steroid therapy, pain medication, and seizure medication.

Prognosis

Meningioma is the most common brain tumor and therefore the best prognostic information is available regarding this tumor type in the dog and cat. Prognostic information is often expressed in time until euthanasia. Happily most patients live pain free and have a high quality of life up until the time of euthanasia. Euthanasia is often performed due to refractory seizure or a sudden decompensation to the clinical signs that existed prior to treatment.

The prognosis for canine meningioma treated with steroid and seizure medication is thought to be very poor with most dogs surviving only about 3 months. This time can be extended to about 6 months with the addition of a relatively safe and very well tolerated chemotherapy called hydroxyurea. Surgery plus hydroxyurea or radiation therapy alone are thought to provide about 1 year. Surgery plus radiation may result in an average survival of about 11/2 years.

Surgery in cats for meningioma is typically recommended because success rates (complete removal, return to normal) are about 95%. There is about a 15% chance of recurrence with meningioma surgery in cats. In dogs, the success rates are slightly lower and the recurrence rate much higher. Radiation therapy is often recommended after or instead of surgery in dogs with meningioma.

When the tumor type is something other than a meningioma, surgery is thought to carry a poorer prognosis, although this is not likely to be uniformly true. Some tumor types (glioma, nasal tumors) likely carry a worse prognosis than meningioma while round cell tumors (lymphoma, reticulosis) likely have a better prognosis. With radiation therapy, across all tumor types, patients are thought to survive on average at least a year.

Information coming soon!


The Pug, Maltese, Yorkie, Chihuhua and all small breed dogs 1-6 years of age are at higher risk.

Symptoms

The signs of disease depend on which part of the brain is affected but can include seizure, confusion, sedation, poor balance, weakness, and with progression: stupor, coma and death. Because the meninges are affected, pain is often also part of this condition.

Diagnostics

To diagnosis ME requires both a MRI and spinal tap. The MRI is used to rule out certain diseases like hydrocephalus and brain tumor. A cerebrospinal fluid (CSF) analysis is often performed to better characterize the disease and better rule out infection. Lastly, a trial with antimicrobial medication and infectious disease testing can be performed to try to identify an infection.

Treatment

A dilemma in the treatment of ME is that an infection requires an antimicrobial (antibiotic, antifungal) and a functional immune system, whereas an immune disease requires immune suppression. Therefore the treatment for one condition, if inappropriate, might cause the other condition to get rapidly worse. Worst still is that some of these conditions are fatal if not treated promptly. We will treat non-infectious ME with a steroid plus immune suppressive medications (cyclosporine, azathioprine, leflunomide) and/or a chemotherapeutic agent (cytosar, lomustine, procarbazine) and a antiepileptic drug (AED) in the event of seizure. The goal of immune suppression is to obtain a clinically-well patient so that we can reduce or eliminate the steroid treatment.

Prognosis

The prognosis for ME depends on test results and the breed of the patient. Pug dog and necrotizing encephalitis have a very poor prognosis while GME has a relatively good prognosis. Patients with the former often succumb to progressive neurological signs or seizure within 6 months. However, a recent report on a subpopulation of dogs with GME treated with immune suppression reported an average survival of over 5 years.

Cause

Meningoencephalitis (ME) exists when there are inflammatory cells (white blood cells) in the brain and its lining called the meninges. There are 2 groups of causes for ME, infectious and non-infectious and it can be challenging to truly know in which group a particular patient belongs. Most often, an infection is not found and the patient gets a diagnosis of Meningoencephalitis of Unknown Cause (MUA). There are numerous diseases in this group, examples include: necrotizing encephalitis, Pug dog encephalitis, necrotizing leukoencephalitis, granulomatous meningoencphalomyelitis (GME) and lymphoma (which is a form of cancer that can be confined to the brain). These names represent an effort to group non-infectious brain disease by breed and/or microscopic description because some diseases carry a different prognosis or treatment.

Male dogs, larger dogs, older dogs and the Great Dane, Labrador and Boxer are at higher risk for developing diskospondylitis.

Cause

Diskospondylitis is caused by an infection of the intervertebral disc, adjacent vertebral endplates or surrounding soft tissue. Without treatment, the infection can progress causing meningitis and spinal canal disease.

Symptoms

A major sign of this disease is pain, secondary to the inflammation from the infection. The infection is typically in an organ system like the urinary bladder, prostate, or heart valve and carried in the blood to the vertebral endplates. Because there is often systemic infection these dogs are often sick with a fever, no appetite, and weight loss. The disease can progress and cause pressure on the spinal cord from an abscess around the spinal cord (empyema), a slipping (luxation) or even a fracture of the vertebrae. The signs of spinal cord disease can include weakness (paresis) or paralysis, poor coordination (ataxia), and poor sense of limb position (proprioception).

Diagnostics

The diagnosis can be made from an X-ray (radiograph) of the vertebral column but this requires significant bone destruction. Studies have shown that clinical signs must persist for 2 to 6 weeks in order for radiographs to be diagnostically helpful. Magnetic resonance imaging (MRI) is more sensitive and superior for detection of the disease because it can detect subtle changes in the soft tissue or bone and does not require significant bone destruction to be diagnostically helpful.

Shown above is an MRI from a patient with diskospondylitis, a radiograph of this area was also performed and came back normal. The bottom line shows the normal disc (well defined bright spot) and the normal soft tissue under the disc (dark). The top line shows an infected disc, vertebral endplate and soft tissue. The disc space is less bright and expanded because infection has replaced the disc and is eating into the vertebral endplates. In addition, the soft tissue is bright indicating inflammation or infection and the spinal cord just above the disc space appears mildly compressed.

Treatment

Once diskospondylitis is diagnosed an effort should be made to identify the source of the bacterial or fungal infection by doing blood or/and urine testing. If there is compression of the spinal cord or progression of disease despite anti-microbial treatment then surgery is suggested in order to decompress the spinal cord and collect samples for culture. A positive culture would then predict which antibiotic or antifungal would have the highest chance of a treatment success. Initially more than one antibiotic will be used in conjunction with aggressive pain management. Antibiotic therapy should last for at least 6 weeks or 2 weeks beyond resolution of clinical signs, whichever is longer. Some neurologists will choose radiographic resolution of the disease as an end point for treatment, which often necessitates being on antibiotic for 1 year. At BVNS we are also researching the use of C Reactive Protein (CRP) as a biomarker for this disease. It is hoped that CRP will aid in the diagnosis of this disease and in determining when antibiotics can be safely stopped in these patients.

Progression

The prognosis is generally good for this disease.