A neurological disease is one that affects the brain or the system of nerves running throughout the body. The signs of illness can range from very mild (a weakness in one leg) to very severe (the inability to stand). In order for your vet to investigate the disease they need to know where the problem actually lies.
If your pet has difficulty walking this may be because of a problem with the nerves in its leg, pressure on the nerves in its spine (like a slipped disc) or a problem in the brain. Only by careful examination can your vet identify where the problem is likely to be in order to perform the most appropriate tests.
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.
There are some signs (such as epileptic seizures, paralysis, and circling) that unequivocally suggest that your pet has a neurological problem. However, there are other signs (such as blindness, weakness, and lameness) that can be caused by neurological problems or other diseases. A complete physical and neurological examination can help your vet to identify if your pet’s signs are caused by a neurological problem.
The answer to this question is probably the most crucial part of a successful neurological consultation. Contrary to popular belief, even the most sophisticated diagnostic tools, such as MRI, can only look at a small portion of the nervous system at a time. It can save a lot of time and money if your vet knows exactly where to look for a problem before selecting the appropriate test.
Many conditions such as primary (idiopathic) epilepsy may not show up on any diagnostic tests and your veterinarian will only be able to diagnose them by ruling-out other abnormalities in the correct area of the nervous system. A scan performed on the wrong area may result in an incorrect diagnosis if abnormalities that have no relevance to your pet’s problem are seen. These irrelevant changes are also known as incidental findings.
The nervous system is divided into the brain, the spinal cord and the peripheral nervous system. The brain is divided in two main parts:
- The forebrain (or front of the brain) which is important for vision, smell, behaviour and control of movements.
- The mid- and hindbrain (or back of the brain) which control balance, initiation and co-ordination of movements, breathing and heart function, as well as part of the nerves involved in the control of swallowing, and the movement of jaws, tongue, eyelid and eyeball, ears and lips.
The spinal cord is made of cables joining the brain to the peripheral nerves which control the limbs and organs in the chest or abdomen. The spinal cord is protected by the spine (a bony canal) within which it runs. Although a continuous cord the spinal cord is considered in four parts:
- Cranial cervical (in the higher part of the neck).
- Cervico-thoracic (lower part of the neck at junction between neck and chest).
- Thoraco-lumbar (also called “back”).
- Lumbo-sacral (or “lower back”).
Running from the spinal cord are the peripheral nerves taking messages to the muscles and glands of the head (cranial nerves) and the muscles of the limbs.
Each part of the nervous system can be evaluated by testing the animal’s reflexes and responses. These reflexes and responses test specific pathways and functions of the nervous system. By combining their results, your vet can determine if your pet’s problem is affecting the brain, the spinal cord or peripheral part of the nervous system.
Diseases affecting specific parts of the nervous system are collectively called:
- encephalopathies (brain diseases)
- myelopathies (spinal cord diseases)
- neuropathies (peripheral nerve diseases)
- junctionopathies (diseases of the junction between peripheral nerve and muscle)
- myopathies (muscle diseases)
Neuropathies, junctionopathies and myopathies are also called neuromuscular diseases. These terms refer to the part of the nervous system that is affected, as determined by the neurological examination.
The neurological signs relate to the part of the nervous system that is affected and not to a specific disease. Neurological diseases are initially considered in broad terms as:
- vascular disease (defective blood supply or vessel rupture causing bleeding)
- inflammatory or infectious disease
- traumatic disease (spinal or head trauma, acute ‘slipped disc’)
- malformation (cyst, hydrocephalus…)
- metabolic disease (organ dysfunction causing accumulation of substances that are toxic for the brain or insufficient nutrients such as sugar)
- idiopathic disease (disease caused by a functional problem such as a chemical imbalance or disease for which there is no known underlying cause)
- neoplastic disease (cancer of the nervous system or spread from a cancer elsewhere in the body)
- degenerative disease (disease causing degeneration or premature aging of the nervous system)
Your vet may be able to narrow down all the potential causes of your pet’s problems by understanding the course of your pets problem (did the problem start suddenly or more gradually? – have the signs remained the same, got worse or improved?). Further diagnostic tests are then necessary to narrow down even further these possibilities and, if possible, precisely identify the exact type of disease causing your pet’s signs.
Unfortunately it is often very difficult to predict how successful treatment is likely to be on the sole basis of the neurological examination. The outcome will depend on what disease is causing the problem and how advanced it is.
Not only are the signs displayed by your animal not specific to a particular disease, they rarely indicate the severity of whatever disease is underlying them. For example, some conditions such as stroke often have a very good outcome despite causing sudden and often dramatic signs. On the other hand, conditions such as degenerative diseases cause progressive and irreversible signs despite causing very subtle signs initially.