Category: neurological-disease-cat

When your vet examines your pet they are trying to answer four fundamental questions:

• Does your pet have a problem with its nervous system (a neurological problem)?
• Which part(s) of your pet’s nervous system is affected?
• What type(s) of diseases could cause your pet’s symptoms?
• How serious the problem is.

Your vet will be able to get a lot of information about what is wrong with your pet by giving it a thorough examination. However, in most cases examination only provides clues to where the problem is and allows your vet to produce a list of likely causes of the problem. In order to work out exactly what is wrong with your pet, so that the best possible treatment can be recommended, your vet will need to do other tests to identify the exact cause.

If your pet has a neurological disease your vet may want to take blood or urine samples to check that your pet’s kidneys, liver and other organs are functioning well. Sometimes changes in the blood such as low sugar level, abnormal salt balance, toxins not cleared by a failing liver, or an under active thyroid gland can cause neurological signs. A simple blood test will sometimes provide the answer to your pets problem.

The CSF (cerebrospinal fluid) is the fluid that bathes the brain and the spinal cord. CSF collection (also known as a spinal tap) is indicated in most dogs with nervous system disease. This fluid can be collected from the back of the neck or in the lower back. The procedure can only be carried out under general anaesthesia and is associated with rare but significant risks.

Normal CSF contains very few cells and a small quantity of protein. Many neurological diseases, in particular inflammation of the brain, spinal cord and their covering (encephalitis, meningitis and myelitis), can cause changes in the CSF. A laboratory may find increased numbers of cells, changes in the type of cells, elevation in the quantity of protein and these changes may indicate what is wrong.

On rare occasions, certain types of cancer (such as lymphoma) can be detected by examination of the CSF. Unfortunately, taken on their own CSF changes are rarely typical of a specific disease and the results of CSF tests must be interpreted alongside the clinician’s suspicion and results of other tests (blood test, myelogram, MRI or CT-scan).

Spinal X-rays (radiographs) are commonly used in animals with neck or back pain, wobbliness and paralysis. They can reveal fractures, dislocations, infection or cancers of the spine. Spinal X-rays can sometimes indicate a slipped disc but cannot be used alone to confirm such a problem. Unfortunately, because X-rays are much better for looking at bone than soft tissues, spinal X-rays are likely to be normal in conditions affecting the spinal cord such as ischaemic myelopathy, myelitis or meningitis.

Myelography is a special kind of spinal X-ray taken after injection of a dye into the fluid that surrounds the spinal cord. This dye allows the shape of the spinal cord to be outlined so that it shows up on X-rays. Conditions such as slipped disc will cause changes in shape of the spinal cord and are frequently diagnosed using myelography. Although myelography provides accurate information about the shape of the spinal cord (and whether there is pressure on it), it does not allow your vet to look at the spinal cord tissue itself as an MRI scan do.

MRI stands for Magnetic Resonance Imaging. One of the main advantages of MRI over X-rays or CT-scans is that MRI allows a vet to see, in great detail, the brain and spinal cord tissue. MRI has revolutionised the investigation of neurological disease. MRI is non-invasive and painless although the patient does need a general anaesthetic for the procedure.

Contrary to popular belief, it is only possible to scan a small portion of the body at any one time using MRI. Each patient must therefore receive a full examination to ensure not only that an MRI is needed for diagnosis, but also that the correct part of the animal is scanned.

MRI is an essential tool in the diagnosis of brain disease. However, changes observed in the brain may not always be typical of a specific condition changes on MRI may be very similar for different diseases such as encephalitis, tumour or stroke. Other tests such as CSF analysis may help to identify what is causing the changes seen on MRI.

CT stands for computed tomography and is a special kind of X-ray which allows 3-dimensional pictures to be created. CT gives better details of bones (skull, spine, and joints) than MRI, but MRI is better for looking at soft tissues such as the brain or spinal cord.

EMG stands for electromyography. A very fine needle is inserted in a muscle to detect any abnormal electrical activity. The test is used to look for muscle disease (myopathy) or nerve disease (neuropathy). Although an EMG cannot say what disease is causing the problem, it is a useful test to show which muscles and nerves are affected. EMGs must be performed under general anaesthesia.

Biopsy (or tissue sampling) is an important tool to determine the exact type of cells within abnormal tissue. Most neuro-diagnostic tests are very good at detecting abnormality but not as good as finding out what is causing it.

For example, MRI may reveal a mass within the brain but it cannot say whether this is a cancer, abscess, inflammation, or bleeding. Although in many cases the mass will be a cancer, the only way to confirm this is to take a sample of this mass either by biopsy (using guidance of a CT-scan or ultrasound-scan) or after it has been surgically removed.

Samples of tissue from inside the brain are only rarely taken in veterinary practice. In many practices samples of muscle and nerve tissues are routinely sampled.

Ischaemic myelopathy is a disease of the spinal cord (myelopathy) caused by a poor blood supply (ischaemia). Like any other part of the body, the spinal cord relies on a permanent blood supply to bring nutrients and remove waste products. Arteries supply defined segments of the cord on each side. If one of these arteries becomes blocked the blood supply to a particular area of the spinal cord is shut off and this causes damage to the nerves running there.

The most common cause of blockage is a fragment of the cushion (disc) between the bones in the back. This disc is made of a tough cartilage (fibrocartilage) and so the term fibrocartilagenous embolism (literally meaning fragment of fibrocartilage blocking an artery) is often used to describe the condition. There are many theories, but no-one really knows how or why this fragment of intervertebral disc suddenly gets into the spinal cord artery. There are many other more unusual causes of blockage (a fragment of tumour or fat).

Ischaemic myelopathy is only occasionally seen in cats. This condition can cause paralysis of one back leg, both back legs, all four legs or only one side of the body (depending on which portion of spinal cord is affected). Typically, this paralysis comes on suddenly, is not painful and does not get worse with time (at least after the first 24 hours).

Other diseases that cause sudden paralysis and may be mistaken for ischaemic myelopathy include spinal fracture or dislocation (“broken neck” or “broken back”), spinal cord bruising (spinal cord contusion) caused by a road traffic accident or a bad fall. “Slipped disc” (intervertebral disc herniation) is considered rare in cats and often seen as a result of spinal trauma.

A diagnosis of ischaemic myelopathy is often made by ruling out other causes of acute paralysis (see above). For this purpose, diagnostic tests such as spinal X-rays, myelography and/or MRI scan are indicated. It is important to rule out other conditions causing pressure on the spinal cord (slipped disc or spinal fracture/dislocation) where an operation might be needed.

In most animals with ischaemic myelopathy the results of these tests come back as normal. Since your vet is relying on absence of findings on X-ray or MRI scan to make a diagnosis it is essential that the correct portion of the spinal cord is checked. Occasionally, swelling of the spinal cord can be detected on X-rays or MRI scan.

A definite diagnosis of ischaemic myelopathy and identification of its exact cause can only be made by examining the spinal cord after death.

There is no specific treatment for ischaemic myelopathy but most cats tend to recover within a few weeks provided they have retained the ability to feel pain in their feet. Good nursing care (physiotherapy, assisted walking, hydrotherapy, adequate bedding to prevent bed sores) is essential for the recovery of the animal. The recovery period may be long and require intensive nursing so can be quite expensive.

If your cat did not lose sensation in its feet then it will probably recover over a few weeks. Most cats will make a full recovery after 8 to 12 weeks but some may keep some residual deficits. In animals where there was complete paralysis, improvement may not be seen for a number of weeks and some animals may never fully recover.

The central nervous system (CNS) is the control centre for the body. It is made up of the brain, spinal cord and the covering of these, the meninges. Inflammatory CNS disease is a broad term used to describe a number of conditions causing inflammation of structures in the CNS.

Depending on which part of the CNS is involved, inflammatory CNS disease can be more precisely divided into meningitis (inflammation of the meninges), encephalitis (inflammation of the brain) and myelitis (inflammation of the spinal cord). Each condition can occur on its own, but more usually the conditions occur in combination (e.g. meningo-encephalitis, meningo-myelitis).

Inflammatory CNS disease can be the result of either infectious or non-infectious disease. In humans viral and bacterial meningitis are common causes of inflammatory brain disease. In animals infectious causes are probably the least common cause of inflammatory brain disease but include a number of infectious agents such as viruses (distemper in dogs, and Feline Infectious Peritonitis [FIP] or Feline Immunodeficiency Virus [FIV] in cats), bacteria, protozoa (Toxoplasma, Neospora) or fungi.

Non-infectious inflammatory diseases are more common. Other rare non-infectious causes include precancerous changes (inflammation that will turn into cancer with time) and paracancerous disease (cancer elsewhere in the body causing a reaction in the brain).

The signs of inflammatory CNS disease depend on which part of the CNS is affected (i.e. brain, spinal cord and/or meninges).

Compared to dogs, meningitis is rare in cats. When meningitis occurs on its own, pain, stiffness of the gait, reluctance to move the neck and a hunched back are the most common signs. The signs seen with encephalitis and myelitis vary according to the part of the nervous system that is inflamed but often include seizures, head tilt, depression, neck pain and ataxia.

Unfortunately, the diagnosis of inflammatory CNS disease cannot be based solely on the signs shown by a patient. Other neurological conditions such as brain cancers, and bleeding into the brain can potentially cause similar signs. Even the most severe meningitis or encephalitis may not show up on any blood test.

Further tests are always required and special imaging studies such as a CT or MRI scan can help your vet to make a diagnosis. Collection of fluid from around the brain (cerebrospinal fluid analysis) is one of the most useful tests. This can help to confirm the presence and type of inflammation and, perhaps more importantly, tests can be carried out to look for an infection. It is rare for cerebrospinal fluid to be normal if an animal has inflammatory CNS disease.

Treatment of inflammatory CNS disease depends on the primary cause. Bacterial infections can be treated with antibiotics and other drugs may be available for fungal and viral causes. In non-infectious disease, drugs are used to try to counteract the over-excitation of the immune system. High doses of steroids (prednisolone) is the mainstay of treatment, but other powerful drugs such as azathioprine, cytarabine, mycophenolate, cyclosporin, and cyclophosphamide can also be used in combination. Once the inflammation has been controlled using high doses of medication, drug doses are slowly reduced.

The long-term aim is to take the animal off any drugs but usually a low dose of medication is needed to control the signs. Steroids have many side-effects when used in the long term and this is why your vet will try to minimise the drug dose or combine treatment with other drugs. The main risk of using the other more powerful drugs is that they can affect the bone marrow making your pet more prone to infection.

In most animals, inflammatory CNS disease can be controlled. This means that your pet can lead a normal life (although they may need to remain on medication for many months or even years). Unfortunately, a small number of animals with very severe disease may not get better despite treatment. Other animals appear to get better but experience relapses months after being taken off medication.