Animals with brain disease may show sudden, dramatic signs and become very poorly extremely quickly. In other cases the signs are more vague and it may be some time before your vet gets to the bottom of the problem. Diseases affecting the brain are not limited to brain tumours and include conditions affecting the blood supply (stroke), causing inflammation (meningitis or encephalitis), trauma or malformation of the brain. Many of these diseases can be treated (or at least managed successfully) to give your pet a good quality of life, so it is very important that conditions are investigated and an accurate diagnosis made so that the best treatment can be given.
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 and include the breed-specific disorders of Yorkshire terriers, Maltese and Pugs, and other diseases such as granulomatous meningo-encephalitis (also known as GME). GME is probably the most common cause of inflammatory CNS disease in dogs and is thought to be an immune-mediated disease. Why the immune system suddenly becomes over-excited and decides to attack the CNS is a mystery.
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).
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. Fever is only seen in less than half of the cases and its absence can therefore not be used to discount the possibility of meningitis.
The signs seen with encephalitis and myelitis vary according to the part of the nervous system that is inflamed but often include seizures, 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.
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.