Arthritis in Dogs and Cats
This refers to inflammation of a joint and this can be caused by several different mechanisms. The joint itself can be subdivided into several different components, The bones covered in articular cartilage; the synovial membranes which join the surfaces together (joint capsule) and the synovial fluid which provides the lubrication and a lot of the nutrients for the joints. Peripheral to these structures are the ligaments, tendons and muscles which support and mobilize the joints.
The disease can be subdivided into two principal categories,
· Degenerative
· Inflammatory
I will concentrate principally on the degenerative arthritis called osteoarthritis. Compared to the dog, cats are fortunate to suffer relatively infrequently from osteoarthritis although it is still the most common long term manifestation lameness in the cat.
OSTEOARTHRITIS
Osteoarthritis is a non-inflammatory, often inherent condition of movable joints that result in changes to the cartilage surfaces and their surrounding tissues with cartilage erosion, new bone formation and remodeling with the new depositions of bone to develop changed and irregular surfaces leading to joint pain, stiffness, swelling and limitation in movement with deterioration with age.
How does it occur?
There is little doubt that certain breeds have an inherited predisposition to osteoarthritis. This is known as primary osteoarthritis and conditions such as hip dysplasia in the German Shepherd dog and Burmese cat would be a good example. Questioning breeders on whether arthritis has been known in their breed lines prior to purchase of a pedigree pet is recommended. Mixed breed animals suffer this condition much less frequently.
Secondary osteoarthritis is more common and arises from some insult of the joint such as a traumatic injury resulting in joint instability such as the tearing of cruciate ligaments or abnormal concussive stresses on the joint surfaces caused by obesity or markedly excessive activity.
How do you diagnose it?
If a single joint has been damaged lameness is shown by a nodding action of the head or the ’dropping of a hip’ while walking. Where multiple joints are involved, as is often the case, signs may be less obvious as the pet takes on a compensatory gait, balancing out the limbs with slower movement, reduced propulsion and a less active state. Many pets show stiffness after rest and difficulty in rising with it improving with gentle movement. If your cat has started to slow up and shows less 'spring in his legs', it probably has arthritis. Cats rarely show acute pain (they rarely cry out) but increased nervousness, aggression and depression may all be related to chronic pain.
Your vet will diagnose the condition by reviewing the history, observing the clinical signs and palpating the joints. Radiographs may be necessary, as may analysis of joint fluid (the latter to largely eliminate other reasons for joint damage).
Veterinary scientists in Philadelphia at Penn School of Veterinary Medicine have developed a radiographic technique called “PennHIP. They found that laxity in the hip joints of immature dogs – strongly correlates with the advent of hip arthritis later in life. “The relationship between hip laxity and arthritis in dogs is akin to the relationship between high cholesterol and heart disease in humans” according to Dr. Gail Smith, professor of orthopedic surgery and chair of the Philadelphia Dept. of Clinical Studies at Penn school of veterinary medicine. Hip laxity is no guarantee of arthritis later in life, but is a very solid risk factor.
The PennHIP positions dogs differently than traditional radiography of the hip. With PennHIP, the veterinarian takes one image of a sedated dog hip in the conventional position. Then, with the hips in a more neutral position, this image is supplemented with two others: one with the femoral head pushed in toward the hip socket and one with it pulled away from the socket. Comparing the latter images lets clinicians determine how many millimeters of play exist between femur and socket. For those with several millimeters of excessive play between the ball of the femur and the hip socket a strong correlation exists with hip arthritis later in life.
This techique gives dog breeders an additional tool they may use in their efforts to decrease the incidence of hip dysplasia.
Treatment
The secret of successful treatment is early diagnosis and careful management. Treatment can be divided into three areas:
· Weight control.
· Surgical. Only suitable for specific cases where instability could be corrected by ligament repair or when other solutions have proven ineffective. An example would be where severe arthritis of the hip may respond to surgery.
· Medication. This is a vast topic and depends on the individual case and the severity of problem. It can be divided into conventional and non-conventional therapy
Non-conventional therapy:
· Nutraceutical extracts containing chondroitin and glucosamine associated with manganese salts. This group of natural products, extracted from a range of animals from shark fin to cockerel comb has scientific support to suggest benefits to joint function so long as the disease is not too far advanced. There are some great product formulations with added Methyl Sulfonyl Methane (MSM) and anti-oxidants such as vitamin C & E; called CORTA-RX from Bioniche and RECOVERY-SA from Biomedica.
Conventional therapy:
This is largely divided into four groups:
· Use of NSAIDs (non steroidal anti inflammatory and pain relief drugs) There are many products available for dogs, but very few are licensed for use in the cat and none for long term use due to potential toxic effects. Occasionally they can cause stomach upsets and should be discontinued if vomiting, diarrhea or loss of appetite occur. They should be used under very careful veterinary supervision if there is any suggestion of blood disorder, kidney, liver, heart disease or gastro-intestinal ulceration. Drug interactions can occur (e.g. with steroids). Given short term by injection but more normally by the oral route, with food.
· Polysulphated glycosaminoglycans (PSGAGs) have anti-inflammatory activity and help modulate cartilage and synovial membrane metabolism. Usually given as weekly injections for a month and then every few months.
· Hyaluronic acid derivatives have similar functions to PSGAGs.
· Steroids can be used to suppress inflammatory changes on the joint surface but should only be used where there is inflammatory erosive osteoarthritis present.
Research
Starting in September 2005, veterinary scientists at the University of Liverpool recruited 20 Labrador dogs to a new study into osteoarthritis of the elbow.
The study will help vets understand how osteoarthritis progresses in dogs and how treatment may slow the disease down.
A mobile Magnetic Resonance Imaging (MRI) scanner will make regular visits to the University’s Small Animal Hospital to monitor arthritis in the dogs over a period of six months. This is the first time that the hospital will have on-site access to MRI.
In Labradors the elbow joint is commonly affected and the progress of the disease can be quite rapid, with some Labradors disabled at just six months of age. Current treatments include arthroscopy to relieve pain, but as yet there is no cure for the disease or method to slow its progress.
Veterinary surgeon, Andrew Maclaughlan said: “Until the advent of MRI there was no non-invasive way to evaluate cartilage, so we are fortunate to have this technology available to us at the hospital. The benefit of this simple procedure means that we do not have to put the dog through surgery to look at the joints.
“We will use MRI to look inside the elbow joint of dogs up to two years of age. The procedure will be repeated a number of times over the course of six months to help us build detailed images of how the disease progresses. With the possibility of new treatments to slow down the progression of arthritis, it is important that we develop ways to measure the effect of such drugs and MRI scanning allows us to do this in a safe and detailed manner.”
An MRI scanner is a large cylinder that runs through a magnet. The patient lies inside the cylinder and radio waves are then sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a 2D or 3D image of different tissue types.
With continued research into the causes, progression of disease and new treatments, hopefully we can help our furry friends to enjoy a longer more comfortable life.
William M Golbeck BSc DVM
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