M:F 4:1, age: 20-40 m/c. Clinic LBP/stiffness, reduced rib expansion <2 cm is > specific than HLA-B27, progressive kyphosis, risk of Fx’s.
Imaging steps: 1st step-x-rays to id. Sacroiliitis/spondylitis. MRI & CT may help if x-rays are unrewarding.
Labs: HLA-B27, CRP/ESR, RF-
Rx: NSAID, DMARD, anti-TNF factor therapy
Key Imaging Dx: always presents initially as b/l symmetrical sacroiliitis that will progress to complete ankylosis. Spondylitis presents with continuous ascending discovertebral osteitis (i.e., marginal syndesmophytes, Romanus lesion, Anderson lesion), facets and all spinal ligament inflammation and fusion with a late feature of “bamboo spine, trolley track, dagger sign,” all indicating complete spinal ossification/fusion. Increasing risk of Fx’s.
Key Dx of Sacroiliitis
Blurring, cortical indistinctness/irregularity with adjacent reactive subchondral sclerosis initially identified primarily on the iliac side of SIJs.
Normal SIJ should maintain a well defined white cortical line. Dimension 2-4 mm. May look incongruous d/t 3D anatomy masked by 2D x-rays.
Key Imaging Dx In Spine
Marginal syndesmophytes and inflammation at the annulus-disc (above arrows) at the earliest dx; by MRI as marrow signal changes on T1 and fluid sensitive imaging (above top images).
These represent enthesitis-inflammation that will ossify into bamboo spine.
Lig ossification: trolley track/dagger sign
AS in extraspinal joints: root joints, hips, and shoulders
Less frequent in peripheral joints (hands/feet)
All seronegatives may present with heel pain d/t enthesitis
Complication: Above Carrot-stick/chaulk-stick Fx
PsA & ReA (formerly Reiter’s) present with b/l sacroiliitis that virtually identical to AS
In the spine PsA & ReA DDx from AS by the formation of non-marginal syndesmophytes aka bulky paravertebral ossifications (indicate vertebral enthesitis)
For a clinical discussion of Spondyloarthropathies refer to: