Inflammatory arthritis

Last revised by Daniel J Bell on 3 Jul 2023

Inflammatory arthritides, also known as arthropathies, are a group of joint disorders associated with synovitis and synovial hyperplasia caused by an influx of inflammatory cells. Inflammatory arthritides might also show extra-articular inflammation such as tenosynovitis and enthesitis and might be associated with involvement and inflammatory conditions of other organs.

The following arthritides are included in the spectrum of inflammatory arthritides 1-5:

Inflammatory arthritis is characterized by pain, swelling and stiffness of the joint. Duration of stiffness is prolonged and improves with activity.

Radiographic features associated with inflammatory arthritis include 2,3:

Ultrasound can nicely visualize and assess the above features 2,3:

  • joint effusion: hypoechoic to anechoic intra-articular fluid

  • synovial hyperplasia: non-displaceable hypoechoic intra-articular tissue

  • bone erosions: juxta-articular bone defect visible in two perpendicular planes 

  • tenosynovitis: hypoechoic or anechoic tissue ± fluid within the tendon sheath 

  • enthesitis: insertional hypoechoic tendon or ligament alteration or thickening associated with bony changes including bony erosions and new bone formation

MRI can assess the joints as a whole. In addition to the depiction of synovitis, synovial fluid, tenosynovitis, bony erosions and signs of enthesitis, it is able to demonstrate bone marrow edema and osteitis, which has prognostic value 8.

Synovitis, tenosynovitis and osteitis can be characterized by the following signal changes 8:

  • T1: low signal intensity

  • T2FS/STIR: high signal intensity

  • T1C+ (Gd): contrast enhancement

The radiology report should include a description of the following features and their location:

  • synovial hyperplasia/synovitis and joint effusion

  • bone erosions, their location within the joints as well as signs of new bone formation

  • tenosynovitis

  • enthesitis/enthesopathy

  • osteitis

  • symmetrical/asymmetrical involvement

Differentiating inflammatory arthritis can be challenging early in the disease. 

Features that point towards rheumatoid arthritis include the following 9:

  • symmetric synovitis (bilateral involvement of the wrists, MCP and PIP joints, no absolute symmetry)

  • early flexor tenosynovitis

  • bone erosions in bare areas

Features that point towards spondylarthritis include the following:

  • enthesitis/enthesopathy

  • bone formation

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