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Among patients diagnosed with axial spondyloarthritis (axSpA), "diagnostic uncertainty" persisted in nearly one-third 2 years after their initial classification, researchers said.

Data from the so-called , indicated that, out of 552 patients with suspected axSpA tracked for 2 years, 30% were still in the "suspected" category at the end of follow-up, with probabilities ranging from most likely to very unlikely, according to Mary Lucy Marques, MD, MSc, of Leiden University in the Netherlands, and colleagues.

In another 30% their axSpA diagnoses were upgraded to "definite," while the remaining 40% decidedly did not have the disorder as currently defined, the researchers .

While only "modest" help was provided with repeated workups, it did appear that obtaining new MRI scans over time did increase the certainty in one subgroup: men positive for HLA-B27, a common but imperfect biomarker for axSpA.

The problem, of course, is broader than just axSpA: chronic back pain is one of the most common medical complaints among adults, and it's also common for patients to seek visit after visit, doctor after doctor in a vain quest for relief. Meanwhile, while axSpA is a recognized and distinct entity, its clinical symptoms differ little if at all from unspecified back pain. Radiography helps but nonradiographic axSpA is also a recognized entity.

To examine in detail how the diagnostic progression works in actual patients, Marques and colleagues drew on data from SPACE, which enrolled patients during 2008-2016 who had chronic back pain lasting less than 2 years. They were then followed for up to 2 years. Diagnoses were made at three clinics in the Netherlands and one in Norway.

For the current analysis, the researchers included 552 patients for whom axSpA was considered a potential cause. Of these, 317 were tracked for the full 2 years. Outcomes were determined directly, not from national register data, so losses to follow-up were inevitable.

At the first visit where at least a tentative diagnosis was made, 32% were determined to have definite axSpA. In 40%, the disorder was ruled out entirely; the remainder were about equally divided between uncertain axSpA and uncertain something else.

Although it might appear that those initially diagnosed with definite axSpA mostly retained it through follow-up, about one-third did not. Of the 175 initially considered definite, 133 were still so at 2 years. Meanwhile, about one-quarter of those with uncertain axSpA, 16, were upgraded to definite. Few of those for whom axSpA was considered unlikely or impossible eventually got an upgrade to more likely axSpA.

But an initial diagnosis of definitely not axSpA was also not totally reliable: of 220 so classified at baseline, 65 had a less certain diagnosis 2 years later.

Marques and colleagues looked for but didn't find any particular diagnostic features that pointed especially well to definite axSpA. For every one of the dozen examined, substantial numbers of patients carrying it nevertheless could not be diagnosed with certainty. It was true, of course, that patients with many characteristic features such as sacroiliitis were more likely to receive a definite diagnosis than those with only a few.

Limitations included the mostly white European sample and its conduct in academic medical centers. The lack of follow-up beyond 2 years might also be considered a limitation.

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