Rheumatologists can reliably diagnose axSpA shortly after the onset of symptoms, supporting the need for prompt referral to a specialist as soon as the condition is suspected, researchers say.

The study showed that most patients with chronic back pain of less than two years’ duration can be “unequivocally and reliably diagnosed at their first assessment” by a rheumatologist.

When a diagnosis is uncertain, most patients can be referred back to a general practitioner, as the yield of repeated assessments in secondary care was only ‘modest’, the findings suggest.

The European study, published in Annals of the Rheumatic Diseases, analysed two-year data on patients aged more than 45 years who had experienced chronic back pain of unknown origin for over three months and less than two years.

Following a referral to a rheumatologist, patients underwent a diagnostic workup consisting of evaluation of clinical SpA features, acute phase reactant, HLA-B27, radiographs and MRI scans of the sacroiliac joints and spine, with repeated assessments after three months, one year and two years.

Data revealed that of 552 patients with CBP, nearly one-third (32%) were diagnosed with definite axSpA (d-axSpA) at baseline and 30% at two years.

Of the 70% of patients without a d-axSpA diagnosis at two-year follow-up, 53 had ‘most likely’ and 13 ‘possible’ axSpA. In contrast, according to the paper, 14 had ‘possible non-axSpA’, 84 had ‘most likely non-axSpA’ and 223 had ‘d-non-axSpA’.

The authors noted that baseline diagnosis “remained rather stable”, with definite axSpA revised to non-axSpA categories in just 6% of cases.

Only 8% of patients without a diagnosis for d-axSpA at baseline were subsequently given one at two years; these patients had a mean of three to four SpA features already reported at baseline.

“Most SpA features were already present at the first assessment, with response to non-steroidal anti-inflammatory drugs and sacroiliitis on MRI appearing as the two most frequent incident SpA features potentially adding to a new d-axSpA diagnosis over time,” the investigators said.

However, they emphasised diagnostic uncertainty persisted in around 30% of patients, although just 5% were of high-degree uncertainty.

Of note, none of the SpA features were sufficient to make a diagnosis of d-axSpA, but HLA-B27 positivity and sacroiliitis on imaging at baseline “discriminated best between the 2y-axSpA and the 2y-non-axSpA categories”.

According to the authors, the study is the first to formally prove that patients with axSpA can be diagnosed by rheumatologists soon after symptoms begin “with an overall mean symptom duration of 13 months”.

 The data indicate that “timely referral of preselected patients to secondary or tertiary care centres seems crucial” and “support the ASAS recommendation of immediate referral of patients with ‘suspicion of axSpA’ to a rheumatologist”, they stressed.