Types of Arthritis

There are actually more than a hundred different disease falling under the umbrella term arthritis. Some of them, like rheumatoid arthritis, are familiar to most of us, while others, such as systemic lupus erythematosus, are as well known. In many respects these various diseases are quite different form one another. What they all have in common, however, are symptoms involving pain and inflammation of the joints.

Rheumatoid arthritis, for example, is an autoimmune disease that involves severe chronic inflammation of the membranes surrounding the ends of the bones at the joints. The cause of rheumatoid arthritis is not known, but experts suspect that it is related to an immune system gone awry.

Unlike osteoarthritis, rheumatoid arthritis is systemic, meaning it can spread throughout the body, with inflammation developing in other tissues, such as skin, muscles, blood vessels, and even the lungs and heart. It can tenderness, pain, and swelling of certain joints, as as generalized symptoms like fever and anemia.

In both humans and animals, however, the most common form of arthritis is osteoarthritis. And as a number of clinical studies have shown, osteoarthritis in animals is very similar to that in humans. It is interesting to note that osteoarthritis appears to progress much faster in dogs than in humans. Substantial osteoarthritis may be seen as early as 3 to 4 weeks after an injury in dogs, whereas a similar injury in humans may take years to lead to comparable changes.

It is a slow, progressive condition involving the breakdown of cartilage, a cushion-like substance that covers the ends of bones where they come together to form joints. As the cartilage wears away, the bones begin rubbing against each other. In the initial stages, there may be no obvious signs. Later, stiffness, limping, or difficulty with normal movements may occur. As the disease progresses, pain invariably develops. In many instances, the pain is mild, but it can become excruciating, causing people and animals to avoid movement whenever possible. Osteoarthritis is a chronic condition, which means it is a long-term disease, even though the signs do not necessarily become worse over time.

The word osteoarthritis is a combination of the Greek word osteo, meaning "of the bone," and arthro, "joint." The word ending itis means that inflammation is involved, although many osteoarthritis sufferers have little or no inflammation.

This is not to say that an animal with osteoarthritis will never experience inflammation. After all, it is a normal result of the body's protection-and-repair process when faced with injury or disease, and even low-grade inflammation causes pain and irritation. To make matters worse, instead of diminishing when tissue repair begins, inflammation can continue and get out of control, causing further tissue damage. Destructive enzymes are the released, encouraging a progressive, gradual degeneration of bone, cartilage, and surrounding tissues.

But with or without inflammation, osteoarthritis is painful, simply because the bones in the afflicted joints are losing their cushioning. When arthritis exists without inflammation, more accurate terms for the condition are arthrosis or osteoarthrosis, meaning "degenerative joint disease." In fact, veterinarian often prefer to use these terms for osteoarthritis, because they are more precise. You may the disease referred to by these and other names. so it is useful to be aware of them. Such terms include the following:

Osteoarthrosis

This means a disease or condition involving physical changes around the joint. This definition is often more accurate, because it does not suggest inflammation.

Degenerative Joint Disease (DJD)

This is a disease caused by the degeneration of a component of the joint, such as the breakdown of cartilage. Some veterinarians like to use this term because, as in the case of osteoarthrosis, it does not imply inflammation is occurring.

Hypertrophic arthritis

The word hypertrophic refers to extra growth. In this form of the disease, there is growth of excess bone or bone spurs on the joints.

Joints That Can Be Affected by Arthritis

When osteoarthritis progresses through the body, it does so asymmetrically and in no particular order. So, for example, only one of an animal's knees may be affected initially. Eventually, however, pairs of joints can become diabeled. Weight-bearing joints, like the hips, knees, and ankles, are a particularly susceptible.

Hip Dysplasia

Hip dysplasia is an inherited condition that is commonly seen. Although no dog is immune to hip dysplasia, large pure-bred dogs are especially prone to it and have a more difficult time dealing with it because of their size. Although dysplasia is not evident in puppies, it can often be seen in radiographs when a dog is 4 to 6 months old. Because this is a congenital condition, dogs that have this problem should not be bred, since they will pass this trait to their offspring.

Ideally, the hip joint consists of a cup-shaped socket and a round ball-type bone that fit snugly together. But in the condition known as hip dysplasia, the joint is malformed, so that the ball and socket do not fit as neatly as they should. As a result, the joint is unstable, allowing excess movement of the bones, which leads to calcium deposits, chronic inflammation, muscle pain in the legs, and breakdown of the hip socket tissue.

Ligament tears in the knee (stifle) joint

The most common cause of arthritis in the knee is a tear of a ligament of the knee, called the anterior cruciate ligament, which makes the joint unstable.

Dislocation of the Kneecap

In this condition, abnormally formed leg bones allow the kneecap to suddenly pop out of its proper position and slide back and forth. Chronic, low-grade inflammation develops from the repeated stress to the joint. This is an inherited condition often seen in smaller breeds of dogs from puppy mills or other poor breeding situations.

Arthritis of the hock or popping hock (ankle) joints - Arthritis of this joint can occur following trauma, such as severely sprained ankle, or from development of bone chips due to osteochondrosis. It is one of the less common places in an animal's body for arthritis.

Degeneration of the Shoulder Joint

The breakdown of the cartilage in the shoulder joints, as well as difficulties with the elbow, may be due to trauma, joint instability, or osteochondrosis. Osteochondrosis is associated with poor breeding, inadequate diet, or a combination of the two. As the cartilage deteriorates, joint tissue becomes inflamed and painful. Arthritis of the shoulder is most frequently seen in larger dogs but may occur in small dogs as well.

Arthritis of the Elbow

A hereditary condition common to larger breeds, this form of elbow dysplasia is similar to hip dysplasia, since it is also a result of malformed bones. As it develops, arthritis of the elbow ans bone chips develop within the joint, causing pain and chronic lameness.

Arthritis of the Wrist (carpii)

Arthritis frequently occurs in this joint in animals that jump, either from high spots to the ground or vice versa, such as dogs who take a flying leap to catch a ball or Frisbee.

Diagnosis of Arthritis

Currently, several promising techniques are being evaluated for diagnosis and assessment of the progression of DJD. These include magnetic resonance imaging (MRI), bone scintigraphy, arthroscopy, and body fluid markers of joint cartilage turnover. Assaying the molecular fragments of cartilage matrix molecules released into joint fluid has been suggested as a means to diagnose, monitor, and provide a prognosis for osteoarthritis.

Although synovial fluid analysis alone cannot always differentiate osteoarthritic joints from healthy joints, it is very valuable in excluding sepsis and immune-mediated conditions (which usually have increased fluid color, elevated total nucleated cell counts, and an increase in PMNs). Evaluation of synovial fluid, in conjunction with history, signalment, clinical signs, physical examination findings, laboratory data, and radiographic findings, is still the best method to diagnose and monitor degenerative joint disease.

NSAIDs Toxicity in Dogs and Cats

Non-steroidal anti-inflammatory agents (NSAIDs) are a class of drugs commonly used in both human and veterinary medicine for treatment of a wide range of conditions such as osteoarthritis, cancer, balanced anesthesia, and perioperative analgesia. NSAIDs provide a cost-effective and convenient strategy for analgesia in painful acute and chronic disease states and procedures. These characteristics have increased the use of NSAIDs for pain control in companion animals. However, the judicious use of NSAIDs must include a balance between relief of symptoms and side effects. The most common NSAID-associated toxicity types in companion animals are renal toxicity and gastrointestinal ulceration. Other less common but potentially life-threatening side effects include hepatotoxicity, platelet dysfunction and bleeding, aplastic anemia, and - with long-term use - possibly decreased bone healing and increased cartilage degradation.

References:
1. The Arthritis Cure for pets by Brian Beale, D.V.M, D.A.C.V.S, and Brenda Adderly, M.H.A
2. Synovial Fluid Findings in Degenerative Joint Disease by Tricia Hans, DVM; Kenneth S. Latimer, DVM, PhD; Bruce E. LeRoy, DVM, PhD; Perry J. Bain, DVM, PhD; Heather L. Tarpley, DVM; Paul M. Frank, DVM
3. Nonsteroidal Antiinflammatory Drug (NSAID) Toxicity in Dogs and Cats: Pathophysiology, 'Diagnosis and Monitoring by Jamie Totten, DVM; Holly M. Brown, DVM, Bruce E. LeRoy, DVM, PhD