How Osteoarthritis Differs from Rheumatoid Arthritis

Age

While osteoarthritis is typically a disease of older people—often thought to be the result of years of wear and tear—RA can come on quickly at any age, even in children.

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.

Related: The Most Common Types of Arthritis, and Who's at Risk for Each

Numbers

Approximately 50 million people in the United States have arthritis, including half of those aged 65 or older.

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 osteoarthritis, the cartilage in the joints wears away with time, leaving bone rubbing on bone. Ouch!

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.)

Medication

Osteoarthritis is treated with steroid injections (into the joint) and oral NSAID drugs like ibuprofen and naproxen (Aleve) to fight pain.

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.

Related: Rheumatoid Arthritis Treatment Options, Ecplained by Doctors

Joints

Both diseases affect the joints, but just where and how they cause trouble differs.

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."

Deformities

Joint deformities are more common in RA than OA. This can eventually lead to joint erosion and displacement.

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.

Nodules

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.

Gender

RA affects about three times as many women as men. Further, evidence suggests that women with RA may have more severe problems due to the disease than men with RA, including enduring more severe pain and depression.

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.

Triggers

The exact cause of each disease is often unclear.

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

As an autoimmune disease, RA can flare up abruptly and then subside in a hard-to-predict pattern that can make diagnosis difficult, especially in its early stages.

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.

Morning Symptoms

Patients with RA will often wake up in the morning with stiffness that can last several hours. Osteoarthritis patients can awake with stiffness as well, but it usually subsides within half an hour—although it can return after physical activity.

"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.

Non-Joint Symptoms

A patient with RA may feel sick overall, with a low-grade fever, fatigue, and muscle pain, says Dr. Danielides. Depression, nerve damage, and dryness of the eyes and mouth are also common.

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.

Longevity

RA can shorten a patient's lifespan by about three years, partly because of the increased risk of heart disease, Evans notes. However, current treatments that target inflammation and the misguided immune response can help.

"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.