Rheumatoid arthritis is an inflammatory type of arthritis that affects women more often than men. This type of arthritis is different from the common degenerative arthritis, called osteoarthritis, which occurs with aging or after injury. Each type of arthritis has distinct characteristics. You may think of rheumatoid arthritis as “sick joints” and osteoarthritis as “achy joints.”
However, types of arthritis are often confused. When people are asked if they have rheumatoid arthritis, about 20 to 30 percent respond “yes” even though rheumatoid arthritis occurs in only about 1 percent of the population. This is a diagnosis made by a doctor, and it requires treatment that is quite different from osteoarthritis. Rheumatoid arthritis is an autoimmune disease, meaning the immune system attacks the body's own tissues, leading to inflammation in the joints and sometimes in other locations like the eyes or lungs.
Rheumatoid arthritis can involve any joint. It tends to be symmetrical, with pain and swelling affecting the same joint on both sides of the body. The most common joints affected are the knuckles and middle joints of the fingers, the wrist, the elbow, and the feet. In contrast, osteoarthritis of the hand affects joints at the end of the fingers next to the fingernail and the middle joints of the fingers. Osteoarthritis also affects the large joints of the hip and knee.
RHEUMATOID ARTHRITIS AND OSTEOPOROSIS: TWO SIDES OF THE SAME COIN
The inflammatory nature of rheumatoid arthritis not only causes local problems in the joints but also generalized bone loss. Both the disease itself and its treatments, particularly the use of steroids, increase bone loss. These observations led to the inclusion of rheumatoid arthritis as a major risk factor for osteoporosis and increased fracture risk. For example, rheumatoid arthritis is one of the criteria used in the fracture risk assessment tool, FRAX, to calculate the ten-year probability of fracture.
The inflammatory disease activity of rheumatoid arthritis and the amount of bone loss are related. Recent research has shed light on the possible mechanisms for these observations and has shown common links between the two processes. The inflammation associated with painful, swollen joints shifts the balance of bone turnover toward more bone breakdown. As a result of the increase in bone breakdown, there is acceleration of bone loss.
Bone breakdown also occurs locally in areas close to the inflamed joints. These lesions, called bone erosions, characterize the profound local effect of inflammation by rheumatoid arthritis on the joints. The local bone erosions may start early in the course of the disease. The bone-breakdown cells, osteoclasts, are responsible for these erosions. Osteoclasts are formed within the inflamed joint and are present in large numbers. However, few bone-forming cells, osteoblasts, are found in joints. Therefore, bone formation in rheumatoid arthritis is essentially absent at these localized sites of erosion. In contrast, osteoarthritis is characterized by the growth of bone protrusions or spurs due to too much bone formation. Bone erosions are not a feature of osteoarthritis.
The signal messenger (called RANKL), which controls the formation, function, and survival of osteoclasts, appears to be the key factor for local and generalized bone loss in rheumatoid arthritis. Inflammatory factors produced during periods of inflammation stimulate the production of more RANKL. Therefore, during increased disease activity, RANKL is increased locally in tissues surrounding the swollen joints and causes increased bone turnover.
TREATMENT TO PREVENT BONE LOSS
The disease course of rheumatoid arthritis tends to be characterized by flares and remissions. A flare is associated with inflammation with redness, pain, and swelling in the joints. General symptoms of fatigue and low-grade fever may also occur. When the inflammation disappears, the disease is inactive and in remission. The goal of therapy is to prevent and stop local bone damage and relieve pain and swelling. Treatment of rheumatoid arthritis usually includes multiple medicines to treat all aspects of the disease. Steroids are commonly used in combination with other medicines classified as “disease-modifying” that slow the progression of the disease. In addition, treatment often includes medicines referred to as “biologics,” which target the immune system.
For generalized bone loss, treatment with medicine that blocks the breakdown of bone preserves overall bone mass and provides protection from bone loss. Therefore, bisphosphonates have been the mainstay of therapy to prevent bone loss in patients with rheumatoid arthritis, particularly those receiving treatment with steroids. The bisphosphonates—Fosamax, Actonel, and Reclast—are FDA-approved for treatment of patients on steroid therapy. If you are taking steroid medicine like prednisone, refer to the previous section titled “Steroid Use: Prednisone” for more details.
Because you may have to take multiple medications to treat rheumatoid arthritis, the once-a-year intravenous administration of Reclast may make it a more desirable option than pills, which require a specific dosing regimen. In addition, a small study suggested that Reclast may also be effective in decreasing local bone erosions.
Recent scientific evidence shows that decreasing RANKL protects against local bone erosions. Prolia, the osteoporosis medicine, works by inhibiting the RANKL messenger. Therefore, Prolia effectively increases bone density and decreases fracture risk. Prolia showed promising results in a small clinical trial in more than two hundred patients with rheumatoid arthritis. One year of therapy with Prolia 60 or 180 mg, given twice at six-month intervals in addition to ongoing use of methotrexate, showed reduction in bone erosions in comparison with the control group taking methotrexate alone. In addition, Prolia increased bone density at the hip and spine. However, Prolia did not have any direct effect on inflammation of the joints.
Future therapies for active rheumatoid arthritis may include Prolia in combination with anti-inflammatory medicines. The addition of Prolia may prove beneficial for preventing both generalized bone loss and local bone erosions. Additional research is underway.
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The Bare Bones
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