Classification Criteria for Axial Spondyloarthritis

Axial SpA — Classification criteria for axial SpA, including criteria for those without plain radiographic changes (nonradiographic axial SpA [nr-axSpA]) and with radiographic (radiographic axial SpA) changes of sacroiliitis, were based upon a large multicenter study [39]. In patients with a history of back pain of unknown origin, which was of at least three months' duration and which began before age 45, the classification criteria for axial SpA exhibited sensitivity of 83 percent and specificity of 84 percent [39]. This algorithm is as follows:

●The entry step is that the patient must have had back pain of any type for at least three months, and the age of onset must be less than 45 years.

●The second step consists of two arms that are evaluated separately based upon the presence either of sacroiliitis on imaging or of human leukocyte antigen (HLA)-B27:

•HLA-B27-positive patients – In patients who test positive for HLA-B27, at least two additional features of SpA from the list below are required for classifying a patient as having axial SpA (see 'SpA features' below)

•Sacroiliitis on imaging – In patients diagnosed with sacroiliitis based upon plain radiographs (structural changes) or magnetic resonance imaging (MRI) (subchondral bone marrow edema [BME]), at least one other feature of SpA from the list below should be present (see 'SpA features' below)

SpA features — The following are SpA features that contribute to the classification criteria for axial SpA (see 'Axial SpA' above):

●Inflammatory back pain – Several definitions for inflammatory back pain have been proposed. For classification purposes, inflammatory back pain can be defined as having at least four of the five following parameters [67]:

•Age of onset <40 years

•Insidious onset

•Improvement with exercise

•No improvement with rest

•Pain at night (with improvement upon arising)

●Other SpA features (each of equal weight) – Other SpA features include the presence of one or more of the non-spinal features noted below. The occurrence can be either before or at the time of evaluation for the following items listed: arthritis, heel enthesitis, uveitis, dactylitis, psoriasis, and inflammatory bowel disease. The features are:

•Arthritis – As diagnosed by a clinician

•Heel enthesitis – Spontaneous pain or tenderness at site of insertion of Achilles tendon or plantar fascia at the calcaneus diagnosed by a clinician

•Uveitis – Confirmed by an ophthalmologist

•Dactylitis – Diagnosed by a clinician

•Psoriasis – Diagnosed by a clinician

•Inflammatory bowel disease – Crohn disease or ulcerative colitis diagnosed by a clinician

•Good response to nonsteroidal antiinflammatory drugs (NSAIDs) – Within 24 to 48 hours

•Family history of SpA – Presence in first- or second-degree relatives of AS or acute anterior uveitis [37]

•Elevated C-reactive protein (CRP) – After exclusion of other causes for elevated CRP

Bhopalwala. H