How Rheumatoid Arthritis Differs From Osteoarthritis
Two different diseases
Most people with arthritis have osteoarthritis, which commonly occurs with age.
But there's another type called rheumatoid arthritis (RA), a serious autoimmune disease. The two are often confused—which can be endlessly frustrating for those with RA.
"Everybody says that arthritis is one word," says Christopher Evans, DSc, PhD, the Maurice Mueller Professor of Orthopaedic Surgery at Harvard Medical School in Boston. "But the conditions are quite different."
Here are 13 ways to tell the two apart.
The average onset of RA is between 30 and 50 years old; osteoarthritis strikes most people later in life. (It's called juvenile RA when it occurs before age 16.)
"Unless you've been banged up on a sports field or in a car crash, it's very unusual to see someone with osteoarthritis at a young age," says Evans.
About 27 million are cases of osteoarthritis and 1.3 million are RA.
Because of the big imbalance in numbers, people often think all arthritis is osteoarthritis, and may say, "Oh, my grandmother has that" to someone with RA, or may not realize that, yes, a child, teen, or young adult can indeed have arthritis.
Source of the pain
In RA, the immune system cells think they recognize an invader and target the synovium, the joint's lining.
Cell-signaling molecules such as tumor necrosis factor and interleukins pour into the blood stream, causing fever, swelling, and other symptoms not seen in osteoarthritis. (The inflammation caused by RA can lead to heart, lung, and eye damage.)
People with RA need these too, plus stronger oral steroids, like prednisone, which can cause bone thinning.
They also need drugs (some of the same ones used in chemotherapy for cancer patients, albeit at lower doses) that prevent joint destruction.
Called disease-modifying antirheumatic drugs, or DMARDs, these meds are known for their effectiveness, as well as their risk of side effects or infections.
RA generally attacks smaller joints first, from the wrists to the toes, leaving them painfully red, warm, and swollen, usually in matching sets, on both sides of the body.
In osteoarthritis, larger weight-bearing joints such as hips and knees usually have the worst damage, and the problem joint may be on one side of the body but not the other.
"Rheumatoid arthritis can spread from one hand to the other and then throughout the body to as many as 30 different joints," Evans says, "whereas osteoarthritis affects a very limited number of joints."
The hands of RA patients can become severely deformed. Fingers undergo a characteristic deviation and can appear pulled out to the side, notes Evans.
Osteoarthritis patients are more likely to develop painful bony lumps or spurs in their fingers, shoulders, elbows, hips, knees, or ankles. People with either OA or RA may need joint replacement surgery.
About 20% to 30% of RA patients will develop firm nodules under the skin, frequently on the elbows, notes Stamatina Danielides, MD, a rheumatology fellow at Columbia University in New York City.
These lumps, which vary in size and can be as large as a golf ball, can be quite painful and are often a sign of more severe disease, she says.
Nodules are not associated with osteoarthritis.
Osteoarthritis, on the other hand, hits the sexes fairly evenly, although the distribution depends on age. While patients under the age of 55 are more commonly men, women tend to dominate later in life.
RA is an autoimmune disorder that causes inflammation in the lining of the joints. Genetics, hormones, smoking, and other environmental exposures, such as viral or bacterial infections, may play a role in setting the immune system on its rampage, notes Dr. Danielides.
There is no immune involvement in the joint deterioration of osteoarthritis. A combination of age, genetics, joint injury, joint overuse, obesity, hormones, and muscle weakness are thought to play a role.
Onset and progression
How the condition flares and progresses can vary widely between patients, notes Evans.
"In rheumatoid arthritis, the immune system is fighting the joint as if it were a foreign object and destroying it," he says.
Osteoarthritis generally develops slowly over many years as cartilage continues to wear down and forces more painful bone-on-bone rubbing.
"A patient with mild to moderate osteoarthritis might get up in the morning, walk a mile to get a newspaper, and then on way back their knees might start hurting," says Evans.
Without treatment for the chronic inflammation, RA can go on to affect "all sorts of organs," adds Evans. Patients are at an increased risk of heart disease and even some cancers.
Osteoarthritis is typically confined to the joints.
"If you get in early enough with the appropriate treatment, the disease can be controlled and many patients can get on with their lives," says Evans.
Osteoarthritis has no specific impact on longevity other than the general effect of making patients less active, Evans adds.