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Spondyloarthropathy, also known as spondyloarthritis

Classification
Spondyloarthropathy is classified into two categories based on the Assessment of SpondyloArthritis International Society (ASAS) classification criteria: primarily axial involvement and predominantly peripheral manifestations.

Axial spondyloarthritis
The patient has to meet two requirements in order to be considered for a diagnosis of axial SpA: they must be under 45 years old and have experienced back pain of any kind for at least three months.

The second step comprises of two sections that are assessed independently according to the existence of either sacroiliitis on imaging or human leukocyte antigen (HLA) B27:
 * HLA-B27-positive patients - To diagnose axial SpA in patients who test positive for HLA-B27, at least two more SpA symptoms from the list below must be present.
 * Sacroiliitis on imaging - When sacroiliitis is diagnosed in patients with structural alterations on plain radiographs or subchondral bone marrow edema (BME) on MRI, at least one additional sign of SpA from the list below should be present.

SpA features:
 * Inflammatory back pain – There are several definitions that have been put forth for inflammatory back pain. Inflammatory back pain is characterized by the presence of four or more of the following five factors:
 * Onset at <40 years old.
 * Insidious onset.
 * Improved with exercise.
 * Not improved by rest.
 * Pain at night.
 * Arthritis.
 * Heel enthesitis.
 * Uveitis.
 * Dactylitis.
 * Psoriasis.
 * Inflammatory bowel disease.
 * Good response to nonsteroidal anti-inflammatory drugs (NSAIDs).
 * Family history of SpA.
 * Elevated C-reactive protein (CRP).

Peripheral spondyloarthritis
The initial requirement is that the patient have at least one of the following three findings:
 * Arthritis.
 * Enthesitis.
 * Dactylitis.

If the patient meets the previous requirements, they must exhibit at least one of Group A's SpA features or two of Group B's SpA features.

Group A SpA features:
 * Uveitis.
 * Psoriasis.
 * Inflammatory bowel disease.
 * Preceding infection.
 * HLA-B27.
 * Sacroiliitis on imaging.

Group B SpA features:
 * Arthritis.
 * Enthesitis.
 * Dactylitis.
 * Inflammatory back pain in the past.
 * Family history of SpA.