How Rheumatoid Arthritis and Osteoarthritis Differ

FEBRUARY 15, 2016
Beth Bolt, RPh
Arthritis is a general term that covers more than 100 diseases and related conditions.1 Inflammation and joint stiffness are at the heart of all forms of arthritis. Arthritic pain may be constant or may come and go. It may occur when at rest or while moving. Pain may affect only 1 joint or show up in different parts of the body. The skin over the affected joint may become red and swollen, and feel warm to the touch.

According to the Arthritis Foundation, rheumatoid arthritis (RA) and osteoarthritis (OA) are the most common types of arthritis, affecting 1.5 million and 27 million Americans, respectively.2,3 These conditions damage joints and affect their function, and although they have some similarities, they are very different diseases, particularly in terms of their causes and their management and treatment.

Table 1: Risk Factors for Osteoarthritis
Excess weight
Previous joint injury
Joints that are not properly formed
Family history
Stress on the joints from certain jobs or sports

OA is caused by aging and regular wear and tear (Online Table 1). In OA, the cushioning cartilage that covers bone joints gradually wears away, which allows bone to rub against bone, leading to swollen joints and painful movement. OA is sometimes called degenerative joint disease or degenerative arthritis. RA occurs when your immune system, which normally defends the body from invading organisms, mistakenly attacks the lining of your joints, causing pain, swelling, warmth, redness, stiffness, and loss of function in the joints, all of which can eventually result in joint deformity (Online Table 2).

Table 2: Risk Factors for Rheumatoid Arthritis
Sex: women are 2 to 3 times more likely than men to develop RA
Age: RA most commonly begins between 40 and 60 years of age
Family history: if a family member has RA, you may have an increased risk
RA = rheumatoid arthritis.

Although both RA and OA can affect the small joints of the hand, there are differences. RA develops relatively quickly over a period of weeks to months and tends to affect the middle joints of the fingers and the knuckle joints (Online Table 3). RA can sometimes affect other organs of the body, such as the skin, eyes, lungs, and blood vessels.

Table 3: Signs and Symptoms of Rheumatoid Arthritis
Tender, warm, swollen joints
Morning stiffness that may last for hours
Firm bumps of tissue under the skin on your arms (rheumatoid nodules)
Fatigue, fever, and weight loss

OA starts slowly, commonly affecting the joints near the ends of the fingers and at the base of the thumb (Online Table 4), and can occur in any joint, but usually affects the hands, knees, hips, or spine. In RA, the same joints are usually affected on both sides of the body. This symmetry does not typically occur in OA, so it is common for only 1 hand or knee to be painful.

Table 4: Signs and Symptoms of Osteoarthritis
Loss of flexibility
Grating sensation in joints
Bone spurs around affected joint

Joints damaged by OA may be stiff in the morning, but they usually feel better within an hour. Joints affected by RA, however, often hurt for more than an hour after getting out of bed.

No single test can diagnose OA. Your health care provider (HCP) may use your medical history, a physical exam, imaging tests, and other blood or laboratory tests to rule out other conditions that might be causing symptoms. Your HCP also may order a test in which fluid is drawn from the joint to rule out infection or gout.

RA can be difficult to diagnose in its early stages because the early signs and symptoms mimic those of many other diseases, including other types of arthritis. As with OA, there is no single blood test or physical finding to confirm an RA diagnosis. An HCP will conduct a physical exam and obtain a personal and family medical history. During the exam, your HCP will check your joints for swelling, redness, and warmth, and your reflexes and muscle strength.

Blood tests can measure inflammation levels and look for biomarkers, such as antibodies (blood proteins) linked with RA. Individuals with RA tend to have an elevated erythrocyte sedimentation rate (ESR, or sed rate) and/ or a high C-reactive protein (CRP) level. Both of these markers indicate the presence of an inflammatory process in the body.

An x-ray, ultrasound, or magnetic resonance imaging scan may be necessary to look for joint damage, such as erosion, which is a loss of bone within the joint and narrowing of joint space. Your HCP may also recommend imaging tests to help track the progression of RA in your joints over time.