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A definitive diagnosis is essential to the optimal management of patients with neurological disease and is achieved through the application of a range of diagnostic tests.
Blood and urine tests
The main aim of these tests is to ensure that the animal's kidneys, liver and other organs are functioning well. Some neurological symptoms can in occasion be caused by changes in the blood composition (low sugar level, abnormal salt balance, toxins not cleared by a failing liver, under active thyroid) and a simple blood test can sometime provides the answer of your animal's problem.
The CSF (cerebrospinal fluid) is the fluid that baths the brain and the spinal cord. CSF collection (also known as 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. This procedure can only be carried out under general anaesthesia and is associated with very uncommon but significant risks.
Compared to blood, a normal CSF contains very few cells and small quantity of protein. Many neurological diseases (in particular encephalitis, meningitis and myelitis - see fact sheet inflammatory CNS disease) can cause changes in the CSF composition (increase in the number of cells, changes in the type of cells, elevation in the quantity of protein). In rare occasion, certain type of tumor (such as lymphoma) can be detected on the CSF. Unfortunately, taken on their own CSF changes are rarely 'typical' of a specific disease and results of CSF must be interpreted according to the clinician suspicion and results of other tests (blood test, myelogram, MRI or CT-scan).
Spinal X-rays (radiographs) are commonly used in animal with neck or back pain, wobbliness and paralysis. They can reveal fracture, dislocation, infection or tumors of the spine. Spinal X-rays can sometime give indication of slipped disc but cannot be used alone to confirm such problem. Unfortunately, spinal X-rays are likely to be normal in conditions affecting directly the spinal cord such as ischemic myelopathy, myelitis or meningitis.
This technique consists to do spinal X-rays after injecting a dye into the fluid that surrounds the spinal cord.
The shape of the spinal cord can therefore be outlined and be evaluated with X-rays. Conditions such as slipped disc will cause changes in shape of the spinal cord and are frequently diagnosed using myelography. Although this technique provides relevant information on diseases compressing the spinal cord, it does not assess the spinal cord tissue itself as MRI scan do.
MRI stands for Magnetic Resonance Imaging. MRI has revolutionised the investigations of neurological disease. One of the main advantages of MRI over X-rays or CT-scanner is its ability to image with great details the brain and spinal cord tissue. Like CT, MRI is also non-invasive and painless although it requires putting the animal through a general anaesthesia.
Contrary to the common belief, only small portion of the body can be scanned using MRI. It is therefore essential that the animal is properly examined to ensure that its problem requires the use of MRI for diagnosis but also that the adequate part of its nervous system 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 as disease such as encephalitis, tumour or stroke can sometimes give very similar changes. The use of other tests such as CSF analysis can give indirect clue of what are the changes seen on MRI and help in the diagnosis of the animal's problem.
CT stands for computed tomography. It is an X-ray technique where a computer is used to reconstruct cross-sectional images of the animal in the scanner. Compared to MRI, CT gives better details of bones (skull, spine, joints) but lesser details of soft tissue such as the brain or spinal cord parenchyma.
EMG stands for electromyography. This test is indicated in animal with suspected peripheral nervous system disease (muscle and peripheral nerve). Although it does not give a definitive diagnosis as to what disease is causing the problem, EMG is a useful test to detect or confirm peripheral nervous system disease as well as mapping which part of the body is involved. A very small recording needle is inserted in the muscle to detect any abnormal electrical activity that could be caused by a myopathy (muscle disease) or neuropathy (nerve disease). This test is done under general anaesthesia.
Biopsy (or sampling) is an important tool to determine the exact type of cells within a suspected abnormal tissue. Most neuro-diagnostic tests are very good at detecting abnormality but not as good as finding out what is the nature of this abnormality. For example, MRI may reveal a mass within the brain but it does not tell you what is the exact nature of this mass (cancer, abscess, inflammation, bleed?).
Although in many cases the mass will be a tumor, definitive diagnosis can only be made after taking a sample of this mass either by biopsy (using guidance of a CT-scan or ultrasound-scan) or after surgical resection. Muscle and nerve are other tissues more routinely sampled.
If you are concerned about the health of your pet you should contact your veterinary surgeon.