Rheumatoid arthritis: from early signs to deformities
Rheumatoid arthritis (Rheumatoid arthritis, RA) most commonly manifests in the hands and wrists, although virtually any synovial joint can be involved. The most vulnerable zones are the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints.
In the modern era of active use of disease-modifying anti-rheumatic drugs (disease-modifying drugs), achieving the earliest possible diagnosis is critical. Conventional radiography remains the traditional imaging foundation. Standard radiographs demonstrate:
- symmetric soft-tissue swelling;
- joint space narrowing;
- erosion formation (in later stages).
However, ultrasound (US) and magnetic resonance imaging (MRI) have become the gold standards for detecting primary synovitis, offering significantly higher sensitivity for detecting erosions compared to radiography.
The earliest erosive defects are usually localized along the radial aspect of the middle metacarpal head. This same zone exhibits localized osteopenia with a specific deossification pattern known as the «dot-dash» (dot-dash) sign. Pronounced erosion of the ulnar aspect is also characteristic of RA.
As the disease progresses, severe biomechanical impairments develop. A classic example is the Boutonnière deformity (Boutonnière deformity). It is characterized by persistent hyperextension of the distal interphalangeal joint combined with flexion of the proximal interphalangeal joint.
Erosive osteoarthritis
Erosive osteoarthritis (Erosive Osteoarthritis) presents a fundamentally different radiographic pattern of involvement. Unlike rheumatoid arthritis, destructive processes affect multiple interphalangeal joints.
The key feature is that erosions form predominantly in the central (subchondral) zone of the articular surfaces. This specific location of defects results in a unique visual phenomenon on the distal articular surface known as the «seagull wing» sign (seagull wing).
Evaluation of imaging in treated inflammatory disease
A distinct challenge is the interpretation of radiographs in patients with treated inflammatory disease (Radiographs in Treated Inflammatory Disease). With successful treatment of rheumatoid arthritis, bone density may be preserved. However, if irreversible joint damage has already occurred, a cascade of changes is triggered, leading to secondary osteoarthritis.
It is crucial for the clinician to recognize this secondary osteoarthritis and avoid mistaking it for ongoing RA activity. Misinterpretation can lead to the unwarranted continuation of inappropriate therapy.
Key criteria for secondary osteoarthritis:
- Proximal distribution of new secondary changes.
- Overlay of fresh proliferative bone formations on top of old rheumatoid erosions.
Seronegative arthritides
Seronegative arthropathies (Sero-Negative Arthritis) comprise a group of interrelated inflammatory joint diseases that share common features but occur without classic serological markers.
The main distinguishing feature of the entire group is the involvement of entheses (enthesitis). This is classic inflammation localized strictly at the insertion sites of tendons and ligaments into bone.
Other features of the group:
- Complete absence of rheumatoid factor (rheumatoid factors).
- A pronounced tendency toward axial skeletal involvement (development of spondyloarthritis, spondyloarthritis).
- Strong association with the histocompatibility antigen HLA-B27. (Important note: the presence of this antigen is neither strictly mandatory for the development of these diseases nor an absolute diagnostic criterion).
Briefly: answers to topical questions
Which specific nosologies are included in the group of seronegative arthritides?
The main nosologies in the seronegative spondyloarthropathy group include:
- Ankylosing spondylitis (Ankylosing spondylitis).
- Psoriatic arthritis (Psoriatic arthritis).
- Reactive arthritis (Reactive arthritis).
- Enteropathic spondyloarthritis (Enteropathic spondyloarthritis).
Differentiating erosions: RA «eats away» at the joint from the edge (radial aspect), whereas erosive osteoarthritis strikes precisely in the center, forming the «seagull wing» sign.
Class and exam questions
Why are hand ultrasound and MRI needed if an X-ray can be performed?
Conventional radiography reveals already established structural defects. Ultrasound and MRI have significantly higher sensitivity, enabling the detection of synovitis and microerosions in the earliest stages.
How does a Boutonnière deformity appear on imaging?
It manifests as hyperextension of the distal interphalangeal joint and flexion of the proximal interphalangeal joint.
What is enthesitis and what conditions is it characteristic of?
Enthesitis is inflammation at the insertion sites of tendons and ligaments into bone. This is the primary characteristic imaging sign of the seronegative arthritis group.
What else to study on this topic
- MRI semiotics of early synovitis: sequences and contrast enhancement
- Pathophysiology of the «dot-dash» deossification pattern formation
- Biomechanics of the tendinous apparatus in the development of Boutonnière deformity
- The relationship between enthesitis and the HLA-B27 antigen at the molecular level
- Radiographic criteria for differentiating primary and secondary osteoarthritis
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