Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis are part of a group of arthritic conditions called seronegative spondyloarthropathies. “Seronegative” means that people with these conditions typically do not have antibodies called rheumatoid factors in their blood. In contrast, established rheumatoid arthritis patients often test positive for rheumatoid factor.
These conditions can produce joint pain that mimics the joint pain associated with rheumatoid arthritis (RA), but they also tend to produce back pain, eye problems, skin rashes, and/or gastrointestinal symptoms.
Ankylosing Spondylitis vs. Rheumatoid Arthritis
In Greek, ankylos means stiffening of a joint, means vertebra, and itis means inflammation. Ankylosing spondylitis is a form of inflammatory arthritis that primarily affects the spine, but it can affect other joints too.
How is it similar to RA? People with ankylosing spondylitis often report morning pain and stiffness. They may also feel feverish and fatigued. Affected joints can feel swollen and tender.
How is it different? Ankylosing spondylitis usually produces symptoms in the low back, hips, and/or shoulders first. In contrast, rheumatoid arthritis usually first affects smaller joints, such as those in the hands and feet (occasionally the knees are the first affected). Some people with ankylosing spondylitis experience eye symptoms, including redness, light sensitivity, and blurred vision.
Both diseases can affect anyone; however, RA is most frequently diagnosed in women ages 30 to 60 and ankylosing spondylitis is more frequently diagnosed in males under the age of 40.1
Psoriatic Arthritis vs. Rheumatoid Arthritis
According to the National Psoriasis Foundation, 85% of people with psoriatic arthritis also have psoriasis, a condition that can cause red, patchy areas of skin and pitted fingernails.2 But a person does not have to have psoriasis to have psoriatic arthritis, and psoriasis is not always obvious (e.g. it may be present in the scalp), so a diagnosing doctor will look for other distinguishing symptoms.
How is it similar to RA? Psoriatic arthritis frequently affects the fingers and toes, as well as the knees, wrists and ankles. Affected joints may be swollen, stiff, and painful, especially in the morning. People may feel fatigued.
How is it different? Psoriatic arthritis usually affects the distal joints of the fingers and toes—distal joints are the joints furthest away from the body, such as the third knuckle of a finger. In contrast, RA commonly affects the first and/or second knuckles of the hands.
In addition, psoriatic arthritis usually causes fingers and toes to swell along their entire lengths, making them look like sausages, and RA causes swelling just at the affected knuckle(s). Psoriatic arthritis does not affect joints symmetrically.
Reactive Arthritis vs. Rheumatoid Arthritis
Reactive arthritis, formerly called Reiter's syndrome, is an autoimmune reaction to a bacterial infection. It typically occurs within a month after a notable illness, such as Chlamydia, a sexually transmitted disease, or a bowel infection, which often causes diarrhea.
How is it similar to RA? Both can cause pain and swelling in the hands, feet, ankles, and knees.
How is it different? Reactive arthritis often causes entire fingers and toes to swell, making them look like sausages, rather than causing just the joint (e.g. knuckle) to swell. It can be accompanied by eye infections (conjunctivitis) and/or urinary problems.
When a patient’s symptoms do not clearly point to a specific spondyloarthropathy, a doctor might make an initial diagnosis of undifferentiated spondyloarthropathy, sometimes called unclassified spondyloarthropathy.
In addition to reactive arthritis, psoriatic arthritis, and ankylosing spondylitis, there are other types of spondyloarthropathies, but these conditions are less likely to be confused with rheumatoid arthritis.