How is undifferentiated spondyloarthropathy (USpA) diagnosed?

Updated: Feb 02, 2021
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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The age of onset for USpA extends over a very wide range, with the peak onset at approximately age 50 years. The male-to-female ratio is 1:3. The onset is usually insidious, and, even after years of active disease, sacroiliitis and spondylitis are either absent or appear very mild on routine radiography.

Clinical manifestations of undifferentiated spondyloarthropathy include inflammatory back pain, buttock pain, enthesitis, peripheral arthritis, dactylitis, and fatigue (see Table 4 below). Extra-articular manifestations are uncommon, occurring in fewer than 10% of patients, and include acute anterior uveitis (1-2%), oral ulcers, rash, nonspecific IBD, pleuritis, and pericarditis.

Table 4. Clinical and Laboratory Features of Undifferentiated Spondyloarthropathy (Open Table in a new window)

Clinical or Laboratory Feature


Inflammatory back pain


Buttock pain




Peripheral arthritis


Dactylitis (sausage digits)


Acute anterior uveitis




Elevated ESR


HLA-B27 positive


ESR = erythrocyte sedimentation rate.

Findings of laboratory studies are generally unremarkable except for the presence of an elevated ESR or CRP level. HLA-B27 antigen is positive only in approximately 20-25% of patients.

These factors, especially the late age of onset, female predominance, and low HLA-B27 positivity, suggest that USpA is distinct from AS and the other classic spondyloarthropathies.

In addition, when these patients are observed over long periods, they rarely develop clinical manifestations or radiographic changes that result in a change of diagnosis. Occasionally, radiographs show evidence of periosteal new bone formation at sites of enthesitis, especially at the insertion of the Achilles tendon or plantar fascia on the calcaneus, or early syndesmophytes on the lumbar spine without bridging.

Although most patients with USpA (>75%) have chronic, active disease and require long-term therapy for ongoing symptoms, some patients have mild and intermittent symptoms that require intermittent symptomatic therapy. These episodes may last from 1-2 weeks to several months, with long asymptomatic periods that do not require therapy.

Most patients respond well to nonsteroidal anti-inflammatory drugs (NSAIDs). The majority maintain good function without progressive disease or clinically significant radiographic changes. A small minority of patients do not respond well to or tolerate NSAIDs. In these patients, treatment progression is similar to that in AS patients, including the use of sulfasalazine, methotrexate, and tumor necrosis factor alpha (TNF-α) antagonists, although no well-designed clinical trials have been conducted on the treatment of USpA.

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