Sudden unilateral anterior uveitis is key to diagnosing spondyloarthropathies

"You should suspect spondyloarthropathy in any patient who comes to you with unilateral anterior veitis of sudden onset," said Dr. Rosenbaum said.

There is controversy among experts as to how often someone who has that presentation and is HLA-B27 positive has a spondyloarthropathy, he continued. "My own bias is that it is 90%. Some would argue that it is as low as 30%, but it is definitely a high proportion of patients."

What to look for Dr. Rosenbaum recommended that diagnosis of spondyloarthropathy should begin with a patient history that includes information on low back pain, peripheral arthritis, diarrhea, abdominal pain, and psoriasis. The history should be taken from every patient, even those presenting with their first episode of suspected iritis or uveitis.

"You are likely to have the opportunity to be the first person to realize that a patient's chronic low back pain is a manifestation of a spondyloarthropathy," he said.

"Think about HLA-B27 typing, but remember that it's not a perfect diagnostic test," he added. "About 6% to 8% of the population is HLA-B27 positive. The majority of people who are HLA-B27 positive never get ankylosing spondylitis, and they certainly never get acute anterior uveitis."

If the patient seems to have chronic low back pain that could be related to the iritis, the definitive diagnostic test is a sacroiliac radiograph; CT or MRI can also be performed.

Ankylosing spondylitis is diagnosed primarily on the basis of the patient history, but physicians must be careful to distinguish inflammatory low back pain from mechanical low back pain.

Inflammatory pain usually starts slowly, compared with the sudden snap that may characterize a disc problem.

The back pain associated with ankylosing spondylitis also is typified by morning stiffness and gets better with activity. In addition, the pain usually persists, while disc-related pain is likely to go away after several months. Mechanical back pain from a disc will follow a dermatomal distribution, while that from ankylosing spondylitis will not.

The two types of back pain also respond differently to therapy.

"A nonsteroidal anti-inflammatory drug is often very effective for ankylosing spondylitis but minimally effective, just an analgesic effect, for mechanical pain," Dr. Rosenbaum said.

Ankylosing spondylitis is defined by the presence of bilateral sacroiliitis with variable spine involvement, moving "from the tail to the nose," Dr. Rosenbaum said.

This disease is common, occurring in up to 1% of the population, he noted.

About 90% to 95% of patients with ankylosing spondylitis are HLA-B27 positive, and in a lifetime, they face a 40% risk of developing acute anterior uveitis.

Reactive arthritis also may go undetected unless physicians look beyond the standard description, which states that the disease follows an infection from an agent such as Salmonella, Shigella, or Chlamydia.

"What is much more common is so-called incomplete Reiter's syndrome or reactive arthritis without that classic prodromal disease," Dr. Rosenbaum said. "The classic triad of arthritis, conjunctivitis, and urethritis occurs, but even as a rheumatologist I see that presentation very rarely."