Category: lameness-cat

The spine is the name given to the collection of bones (vertebrae) inside which the spinal cord is contained. The spinal cord is made of cables of nerves (like the wires running in an electrical cable), linking the brain to the local nerves that control the movement of the limbs and other functions (the peripheral nervous system).

The intervertebral disc is a spongy, doughnut shaped pad in the main joint between the vertebrae. The disc lies just underneath the spinal cord in cats. Each disc has a semi-liquid centre (nucleus pulposus) and a tough outer fibrous layer (annulus fibrosus). The discs form a bridge between two neighbouring vertebrae and act as a cushion, giving strength and flexibility to the spine.

A slipped disc can happen in 2 ways:

1. Rupture of a healthy disc can be caused by trauma (such as a road traffic accident, or a fall from height) with tearing of the annulus fibrosus.
2. Degeneration of the disc is a result of a premature ageing process. This causes progressive thickening of the dorsal part of the annulus fibrosus which presses up on the spinal cord (disc protrusion).

Disc degeneration is more common in the regions of the spine which are particularly exposed to physical stress (the lower neck, mid-back and lower-back). Degeneration can also result in stiffening of the disc as the semi-liquid centre becomes dry and loses its cushioning properties. If this happens the annulus fibrosus can tear allowing the, now stiff, nucleus to bulge out and put pressure on the spinal cord (disc extrusion).

This type of degeneration is mainly seen in breeds with short bandy legs (also known as chondrodystrophic breeds) as these breeds are born with abnormal cartilage. Dachshunds, Shi Tzu, and Pekingese are the most commonly affected breeds and signs usually develop around 2 to 4 years of age.

Spinal pain is the most common sign of disc disease. If your pet has spinal pain they will adopt abnormal posture (low head carriage, rounding of the back), be reluctant to move or exercise, cry when moving around.

A slipped disc can put pressure on the spinal cord, this damages the nerves and causes signs. If the disc slips suddenly there may also be bleeding into the spine which puts even more pressure on the nerves. This can cause any or all of the following signs:

• loss of coordination
• weakness
• paralysis
• lameness
• faecal or urinary incontinence
• loss of sensation in the leg

The signs that develop following disc damage are the result of:

1. Pressure of the herniated disc material on the spinal cord (compression component).
2. Bruising of the spinal cord caused by the impact of the disc as it is herniate (concussion component).

It is not possible to say how much each of these components is contributing to the signs in an individual animal by examination alone. Myelography, CT or MRI scans can help to determine how much the spinal cord is being compressed. However, it can be very difficult to assess how much bruising has occurred (even with the specialised techniques). This concussion can sometimes be seen as spinal cord swelling.

The cables making up the spinal cord are organised into groups depending on their function within the nervous system. The most superficial cables are those running from the leg to the brain. Their main function is to send messages to the brain about the position of the leg and body in space. Because this group of nerves is the most superficial, they are the first to be affected by pressure from a slipped disc. Damage to these nerves results in the animal being wobbly on his legs.

As we move deeper into the spinal cord, the next group of cables are the ones from the brain sending messages to move the legs. Damage to these cables results in weakness of the legs, which can progress to total paralysis.

The deepest cables (in the centre of the spinal cord) are the ones responsible for informing the brain that the bladder is full, and finally the one carrying pain sensation from the limbs from the brain. Loss of function in these cables results in the animal not being able to urinate and being unaware of painful stimulation in the toes.

As an animal recovers from spinal damage, their nerve functions return in the reverse order to that in which they disappeared. Depending on the site of spinal damage (neck, back or lower back), these signs may affect only the back legs or the front ones as well. Rarely, a slipped disc can cause lameness by trapping one of the spinal nerves as it exits the spine.

 

If your pet has any signs of back problems or lameness your vet will want to perform a full neurological examination.

Diagnosis of a slipped disc is rarely possible using standard X-rays alone. A standard X-ray can only show the bones of the vertebrae and not the joints between them (the discs) or the spinal cord running inside them. Sometimes changes seen on conventional X-rays suggest disc degeneration without the animal showing any signs.

A definite diagnosis of a slipped disc can only be made using either myelography (X-rays taken after the injection of dye around the spinal cord), CT (computed tomography) or MRI (magnetic resonance imaging). These special tests help to confirm if there is a slipped disc, where it is and will also show up other causes of spinal pain or paralysis if they are present.

In most cases a slipped disc should be considered to be a surgical disease except where:

• This is the first time the animal has had back pain.
• The animal has a medical condition that contraindicates general anaesthesia.
• The animal has minimal spinal cord compression and it is suspected that spinal bruising is responsible for most of the signs.

Non-surgical treatment consists of strict rest, in a cage or room, depending on the size of your pet), for at least 4 weeks and treatment with drugs that will reduce inflammation and pain. Your vet will want to see your pet regularly to ensure that they are not getting worse without surgery.

Surgical treatment consists in drilling a hole in the vertebrae to remove the part of the IVD that is putting pressure on the spinal cord. Recovery times vary from 1 to 4 weeks. Despite carrying a small risk of causing further trauma, surgery should prevent further deterioration and relapse in the future.

Success of surgery depends mainly on how much spinal cord function has been lost and especially whether or not and for how long the animal has lost the ability to feel pain in its toes. The prognosis is very good for most animals that retain pain sensation. Paralysed cats with no pain sensation in their rear legs have a slightly better than 50:50 chance of recovering the ability to walk unless this sensation has been lost for more than 48 hours, when the prognosis then becomes very poor.

Although surgical treatment is often preferred, cats with mild spinal cord compression or mostly bruising can recover with only rest and eventually anti-inflammatory medication. However those cats that do get to walk again, may take a long time to recover – sometimes from 6 to 12 weeks.

Literally, myositis means muscle (myo-) inflammation (-sitis). This type of muscle disease (myopathy) represents a group of different diseases which all share the feature of inflammatory cells within the muscle. Myositis can affect:

• Just one muscle
• Groups of muscles, e.g. muscles used in chewing found on the top and side of the head (masticatory muscle myositis), or muscles moving the eyeball (extra-ocular muscle myositis)
• All muscles in the body (polymyositis, dermatomyositis and necrotising myopathy).

The inflammation in the muscle can be due to:

• Response of the body to an infectious agent (parasite or virus) within the muscle (infectious myositis).
• Abnormal immune reaction of the body directed against the muscle (immune-mediated myositis). No-one knows why the immune system suddenly becomes over-excited and attacks the muscles in this way in some animals.
• Myositis may also be associated with cancer. Inflammation may develop first and turn into cancer with time (pre-cancerous change), or cancer elsewhere in the body may trigger an immune reaction to the muscle (paracancerous effect).

The signs caused by myositis can vary considerably depending on the muscles affected. An animal with a generalised myositis (polymyositis) has a stiff stilted gait, muscle pain, weakness and cannot exercise normally. In the early stages of disease generalised muscle swelling occurs and later the muscles are wasted.

Other signs associated with polymyositis include regurgitation of food and water, difficulty swallowing and sometimes breathing problems.

Myositis can be confirmed by taking a sample of muscle tissue for examination. This will show the inflammatory cells within the muscle. Other tests may be necessary to eliminate a potential infectious (blood test) or to rule out the presence of a cancer in the body (chest and abdominal X-rays and ultrasound).

Treatment of myositis is usually aimed at trying to counteract the ‘over-excitation’ of the immune system by giving drugs to suppress the immune system (immunosuppressives). The main treatment is usually high doses of steroids (prednisolone). Other immunosuppressive drugs (such as azathioprine or cytarabine) can also be used in combination with steroids. The short-term aim of the treatment is to return the animal to normal using high doses of medication. When the disease is controlled the quantity of drugs is slowly reduced (hopefully without the animal relapsing). The long-term aim is to take the animal off any drugs, but usually this is not possible and a continued low dose of medication is needed to keep the signs at bay.

All drugs can have side-effects and immunosuppressives are particularly powerful drugs. The main risk of using these drugs is that the immune system will be shutdown too much, making your cat more prone to infection.

In the rare cases where cancer or an infection is found to be the underlying cause of the myositis, treatment should be directed against this. Unfortunately, the outlook in these cases is not good.

The outlook for animals with myositis is usually fair – although improvement may not be seen for several weeks. Corticosteroids can cause muscle wastage and this may give the impression that the animal is getting worse, even though the disease is well controlled. Your vet will need to monitor your pet closely whilst it is receiving treatment, both to ensure it is getting better and also to check that the drugs are not causing any serious unwanted effects.

If an underlying cause of the myositis can be identified and successfully treated it may be possible to withdraw medication altogether without the condition relapsing.

Each muscle in the body is controlled by its own nerve, but this nerve does not connect directly to the muscle. At the junction between the nerve and the muscle (also known as the neuromuscular junction) there is a small gap.

Signals travel along the nerve as an electrical current. When the electrical nerve impulse reaches the end of the nerve, the signal must be conveyed across the gap to the muscle. A chemical messenger called acetylcholine bridges this gap. This messenger is released from the end of the nerve, flows across the gap and fixes itself to a specific receptor (acetylcholine receptor) on the muscle. The acetylcholine attaches to the receptor (like a key fitting a lock) and triggers a signal, which causes the muscle to contract. In myasthenia gravis there is abnormal transmission of the message between the nerves and the muscles.

If the muscles are unable to contract properly they become weak. Muscle weakness can affect the limbs so that animals are unable to stand or exercise normally but can also affect other muscles in the body. In very severe cases the muscles involved with breathing can also be affected.

There are two forms of myasthenia gravis: congenital (a disease the animal is born with) and acquired (a disease that develops during the animals lifetime). The most common type of myasthenia gravis is the acquired form. This is seen most commonly in Abyssinians and, a close relative, the Somali.

Animals with congenital MG are born with too few acetylcholine receptors. The acquired form is caused by a faulty immune system. The main role of the immune system is to protect the body against infection or foreign invaders, and this is often done by the production of antibodies. In acquired MG, the immune system produces antibodies (called anti-acetylcholine receptor antibody or AChR antibody) that attack and destroy the acetylcholine receptor.

No-one really knows why the immune system should suddenly decide to attack these receptors in some animals. In rare cases, MG can be triggered by cancer, or be associated with other immune diseases affecting the nerve or muscle. Whatever the reason, when the number of receptors is reduced, acetylcholine cannot fix itself to the muscle to produce muscle contraction and muscle weakness results.

The typical picture of MG is severe weakness after only a few minutes of activity. This weakness might affect all four legs or only affect the back legs. It is frequently preceded by a short stride stiff gait with muscle tremors. As soon as an affected animal rests they regain their strength and can be active for a brief period before exercise-induced weakness returns.

Other signs of MG are related to effects on the muscles in the throat (laboured breathing and voice change). In the most severe form, the animal can be totally floppy and unable to support its weight or hold its head up. Muscle disease (myopathy) or nerve disease (neuropathy) can mimic signs of MG and should be considered in the diagnosis.

Sometimes the diagnosis of MG can be simple but in other animals it is not straightforward. The best test to diagnose acquired MG is a blood test which looks for antibodies directed toward the acetylcholine receptor (anti-AChR antibody titre).

Your vet may need to do other tests to re-enforce their suspicion of MG. One of these is the Tensilon test – in this test a short-acting antidote to MG (tensilon) is injected into a vein. In affected animals there will be a dramatic increase in muscle strength immediately after injection and collapsed animals may get up and run about (however the effects wear off after a few minutes).

Another test used to help make a diagnosis of MG is an electromyogram (EMG). An EMG machine can be used to deliver a small electrical stimulation to an individual nerve or muscle in an anaesthetised animal. Using an EMG machine a vet can evaluate how well the muscles respond to stimulation from the nerves. The machine is used to create an electrical impulse in the nerve.

Diagnosis of the rare congenital form of MG is based on a special analysis of a muscle biopsy.

Other investigations may be required to look for underlying causes of the disease, particularly in older animals. Chest X-Rays can be indicated to look for cancer in the chest cavity and to evaluate possible involvement of the oesophagus and to detect pneumonia secondary to inhalation of food.

Specific treatment of MG is based on giving a form of long-acting antidote. This improves the transfer of the signal from the nerves to the muscle. Depending on individual circumstances, it may be necessary to give drugs that will suppress the immune system to stop it attacking the receptors. If your cat has pneumonia your vet will want to treat that first (with antibiotics and other drugs) before suppressing the immune system.

Prognosis is generally good for a complete recovery unless severe pneumonia, severe difficulty eating or underlying cancer is present. Treatment usually lasts many months and your vet will need to re-examine your pet on a regular basis to check that they are improving. Repeated blood test to measure anti-AChR antibody levels will also be required.

Myasthenia gravis can be a very serious disease. However with an early diagnosis and a high level of care your pet may make a full recovery.

In the normal joint the bone surfaces are covered with a thin layer of smooth cartilage. This is lubricated with a small amount of joint fluid. This structure allows the two surfaces of the joint to slide freely over one another.

In animals with arthritis (also known as osteoarthritis) the cartilage in the joint degenerates and becomes damaged and thinned. The bone surfaces begin to rub together (rather than gliding) causing discomfort as well as further damage to the cartilage. With time new bone may form around the joint and this can cause the joint to become stiff and limit joint movement. Depending on the cause arthritis may affect just one or any number of joints.

In most cases arthritis develops as a consequence of abnormal wear within the joint. This can be due to:

• Instability of the joints, e.g. when ligaments have been damaged
• Damage to or abnormal development of the cartilage in the joint or
• Damage caused by trauma such as joint fractures and chronic sprains

Arthritis causes pain and stiffness in the joints. If your pet has arthritis you may notice they are not as keen to exercise as in the past and they may limp or seem to be stiff (particularly when getting up from rest). This stiffness may get better after being out for a walk, and sometimes cold and/or damp weather may appear to make signs worse.

Animals will sometimes lick continually at a painful joint and those with pale coloured coats the saliva may start to stain the fur darker over the affected joint. Occasionally the joint may appear hot or swollen but more usually you will not be able to recognise any change in the joint. The signs in some animals can be very obvious whereas other pets may just become quieter or more grumpy if they are in discomfort.

Your vet may suspect that your pet has arthritis from the signs you describe. By examining your pet’s legs your vet should be able to identify which joints are painful, stiff or swollen. In order to find out more about what is going on inside the joint your vet may need to do further tests.

X-rays of the joint will help to confirm the presence of arthritis and to identify any underlying causes. Your vet may also take a small sample of fluid from inside the joint for analysis. In some cases blood samples may be required to look for medical conditions that can affect the joints. If your vet suspects that there is an infection in the joint they will want to take samples to try to identify the cause.

The treatment for arthritis depends upon the underlying cause and the joint(s) affected. In almost all cases arthritis is worse in animals that are overweight and unfit. Treatment of osteoarthritis must be aimed at keeping the joint in use, minimising discomfort, and preserving the structures of the joint for as long as possible. Without a doubt the most important therapy for patients with osteoarthritis is the combination of weight control and exercise management, minimising the load on the joint, and maximising the range of movement and the fitness of the muscles around the joint.

Many patients will also benefit from drug therapy for a few weeks or months, and in occasional cases long-term drug therapy is useful. Initially pain relief is important and the most common veterinary analgesics used are the non-steroidal anti-inflammatory drugs (NSAIDs).

If your pet has arthritis your vet may need to treat them on numerous occasions over their lifetime. The treatment used will vary both from one patient to the next, and for an individual patient over time. Your vet may recommend using multiple treatments, singly, or more often in combination, to provide the best immediate and long-term support for each patient.

NSAIDs are commonly prescribed for management of arthritis as they have actions against both inflammation and pain. Occasionally these drugs can cause vomiting or diarrhoea as well as other side-effects. These side-effects mean that there are some warnings against their long-term use in dogs. NSAID use is quite restricted in cats as these drugs can be more toxic in this species.

In the short-term the drugs with the highest impact on analgesia and inflammation are likely to be the first choice. Often these drugs are not needed in the medium or long-term, or they are not licensed for such use due to the cumulative risk of side-effects. In such cases, particularly in cats where the therapeutic options are more limited, alternatives must be sought.

New drugs are becoming available and the development of a successful management plan for arthritis in the individual patient requires regular review of the current medication and how the patient is progressing.

Unfortunately once the cartilage in the joint has been damaged it rarely repairs. However, although there may still be damage in the joint many pets can be made pain free by long-term use of medication and management to control further wear on the joint.

There is a great variation in the severity of arthritis between patients. Many pets cope well with their disease, and lead a full and active life without any veterinary treatment. Some patients require treatment ranging from simple lifestyle changes to complex surgery. The signs of arthritis often vary throughout the animal’s life and often result in the early onset of joint problems in old age.