Keep your superstar pet strong: Understand Rheumatoid Arthritis in Dogs

Dr Arvind Sharma
Seeing your pet in pain is one of the most heartbreaking feelings. Rheumatoid arthritis can leave your pet in severe pain. You need to be aware of early signs so that managing this disease becomes a tad bit easy. –by Dr Arvind Sharma

Rheumatoid arthritis (RA) is an autoimmune disorder causing progressive joint destruction and deformity. It leads to variable degree of incapacitation in pets that very closely resembles the disease in human. It occurs in both humans and canines, but it is not communicable from one another. It may occur in dogs from the age of about two years onwards.

All breeds including mongrels may get the RA but most commonly it occurs in dogs of small and toys breeds. Deformities occur most frequently in small joints like all the joints of paws. It is less frequent in elbow and hind legs joints. Rheumatoid arthritis is usually is bilateral, symmetrical, and polyarticular in nature i.e. the same joints of the left and right paws are affected at one time.

Bane of pain in rheumatoid arthritis
RA mostly causes inflammation or swelling in the lining or synovial membrane of the joints. But in some cases it may also show its affect on skin and lungs, etc. A healthy joint has two bones covered with articular cartilage at the end. Articular cartilage is a type of connective tissue that acts like protective cushion – a lubricated surface for bones to smoothly glide against. A synovial joint is surrounded by a capsule that provides protection and support. The joint capsule is lined with a type of tissue called synovium. The synovium produces synovial fluid, which lubricates and nourishes the cartilage and bones inside the joint capsule.

In RA, the tissue inside the joint is mistakenly attacked by our immune system causing swelling of synovium due to inflammatory reaction. It then grows out over surface of cartilage, producing a tumor-like mass called pannus. The bone, the cartilage and other joint tissues are damaged. RA causes severe joint destruction and deformities. The joint may even fuse as a result of immobility and consolidation.

The joint capsule remains stretched and can’t hold the joint in its position causing the joint to become unstable and it can move into unusual or deformed positions. Joints become inflamed and painful after repeated episodes of flare ups. How and why do pets and people develop RA is a complicated question with no one particular answer. It is generally believed that a complex interaction between genes and environment leads to breakdown of immune tolerance.

Understanding your pet’s immune system and response
Pets like us possess a large number of white blood cells (WBCs) which are a defense system to unwanted foreign invaders that can harm the body’s normal functioning. The defense line put up by the WBCs is a two-tier formation, the innate immune response and the adaptive immune response. The first line of defense is made up of ‘Scavenger cells, e.g. neutrophils and monocyte or macrophages, etc. which are formed in bone marrow and found in most body tissues. They phagocytose the invader by attaching and expanding its surface to surround it or engulf it, and finally killing and degradation of ingested particles If the scavenger-cells find themselves out numbered, and can’t fight the invaders any more, they send message for reinforcement to second line of defense, the adaptive immune system or lymphocyte. It is like BSF calling out the army when the fighting on the border gets out of hand. The lymphocytes are a highly specialised fighting force. They patrol the body looking for intruders such as virus, bacteria or other foreign particles. These patrolling cells are mainly the T-cells. They can recognise the precise biochemical identity of an invader and, once the invader is identified, they send instruction to lymphocyte colleagues B-cells to begin producing antibodies to fight these invaders.
The damage done cannot be reversed
Unfortunately in RA patients, due to defect or failure of the bodily defense mechanism in which antibodies become active against some of the host’s own cells or tissue. In RA, it appears lymphocyte attack otherwise healthy synovial tissue which lines the inside of synovial joints. Actually, it starts when cells of first line of defense get confused and present self-antigen to second line of defense. This little confusion has devasting life long consequences in a genetically predisposed individual, by activation of T-cells responding to some arthritogenic (arthritis causing) agent possibly microbial or to some self-antigen.

Recent studies have shown that dogs with RA have much higher level of antibodies against canine distemper virus in synovial fluid than normal dogs. This indicates that this virus may play role in pathogenesis of the disease. Chronic response inflammation persists since self-antigen can’t be removed from body in a ‘self vs. self’ situation.

T-cells coordinate the progression of inflammation and communicate with B-cells, which produce the antibodies that are important in tissue damage, as well as aiding in diagnosis when identified. Finally, when immune regulatory mechanisms fail, the immune system also activates cells involved in bone formation and degradation ultimately leading to bone erosion and damage.

Because RA can affect different pets in different way, it can’t be predicted how the condition might develop for your pet. Most of the pets with RA will continue having some joint pain, swelling and flare ups. Few (nearly 20 percent) will always have very mild RA. Less than 5 percent will develop severe disease.

Early diagnosis will help in treatment
No single test can give a definite diagnosis of RA in early stages of the condition. Your vet has to arrive at a diagnosis based on your pet’s symptoms, history, and physical examination and the result of X-rays and blood tests. Also there are tests based on antibodies, e.g. Rheumatoid factor or RF. But these tests should be used judiciously along with a clinical history as the tests can be positive in small number of healthy pets as well. X-rays of paws to look for erosions and joint damage can be helpful. But you need to keep in mind that during the early stages of the diseases the joints look normal.

New medications giving a ray of hope in treatment
In the past two decades, the therapy of RA has undergone revolutionary change, reflecting a paradigm shift in treatment approach as well as the introduction of new disease modifying anti-rheumatic drugs (popularly called DMARDs).

Your vet can recommend these as they slow down the progression and preserve joint structure and are highly effective in dogs. Because DMARDs take some time to start working your vet may also give steroid, which can reduce the inflammation and ease the symptoms while the DMARDs, are taking effect.

The treatment will be based on the severity of the diseases in your pet. Your vet might also suggest some lifestyle changes. Follow them for the good health of your pet. Although the damage done cannot be replaced, you can make your pet’s life comfortable and easy with treatment.

(Dr Arvind Sharma is Retd. Deputy Director, Animal Husbandry, Gurdaspur, Punjab)