What is Erosive Osteoarthritis?
Erosive osteoarthritis is a severe inflammatory subset of hand osteoarthritis characterized by subchondral erosions on radiographs, targeting the interphalangeal joints (DIP and PIP), with abrupt onset of marked pain, inflammatory features, and significantly worse functional outcomes than non-erosive osteoarthritis. 1
Clinical Presentation
Erosive OA presents with distinctly inflammatory characteristics that set it apart from typical osteoarthritis:
- Abrupt onset with marked pain and functional impairment, rather than the gradual progression seen in typical OA 1
- Inflammatory symptoms and signs including stiffness, soft tissue swelling, erythema, and paresthesias 1
- Mildly elevated C-reactive protein (CRP) levels that correlate with radiographic severity and number of joints involved 1
- Predominantly affects postmenopausal women with a female-to-male ratio of approximately 12:1 2
Joint Distribution Pattern
The disease selectively targets specific joints with a characteristic pattern:
- Primary targets: Distal interphalangeal (DIP) joints most frequently, followed by proximal interphalangeal (PIP) joints 1, 2
- Less commonly: Thumb interphalangeal joints 1
- Spares: Metacarpophalangeal (MCP) and carpometacarpal (CMC) joints are typically not involved 1
- Bilateral symmetric involvement is characteristic, which helps distinguish it from septic arthritis 3
Radiographic Features
Plain radiographs remain the gold standard for diagnosis and show distinctive features:
- Subchondral erosions are the hallmark finding, appearing as central erosions that may progress to the classic "gull wing" deformity 1, 2
- Progressive structural damage including marked bone and cartilage attrition, joint instability, and eventual bony ankylosis 1
- Standard OA features such as joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts are also present but more severe than in non-erosive OA 1
Important caveat: MRI detects far more erosions than conventional radiographs (80% of joints show erosions on MRI versus only 40% on plain films), particularly marginal erosions that resemble inflammatory arthritides 4. This suggests that erosive changes may be more common in hand OA than traditionally recognized.
Prognosis and Functional Impact
Erosive OA carries a significantly worse prognosis than non-erosive hand OA:
- Long-term functional outcome is worse than nodal OA, with greater hand function impairment 1
- Hand function can be as severely impaired as in rheumatoid arthritis 1
- Prolonged disability in hand function commonly occurs, with potential for permanent deformity 2, 5
Differential Diagnosis Considerations
When evaluating suspected erosive OA, consider these alternative diagnoses:
- Psoriatic arthritis (may target DIP joints or affect just one ray) 1
- Rheumatoid arthritis (mainly targets MCP and PIP joints, wrists) 1
- Gout (may superimpose on pre-existing OA) 1
- Septic arthritis (typically unilateral with severe pain, marked warmth, and systemic signs) 3
Key distinguishing feature: The bilateral symmetric PIP joint involvement with inflammatory features but only mildly elevated CRP strongly favors erosive OA over infection 3.
Pathophysiology
Erosive OA represents a combination of degenerative and inflammatory processes:
- Synovial pathology shows changes consistent with both rheumatoid arthritis and osteoarthritis, depending on disease stage 2
- Central erosions appear to represent subchondral collapse and pressure atrophy 4
- Marginal erosions morphologically resemble those seen in inflammatory arthritides 4
- Etiology remains unclear but hormonal influences (particularly menopause), metabolic disorders, genetics, and autoimmunity have been implicated 2, 5
Diagnostic Workup
When erosive OA is suspected:
- Plain radiographs of both hands (posteroanterior view) are adequate for diagnosis 1
- Blood tests are not required for diagnosis but may help exclude coexistent inflammatory arthritides 1
- CRP measurement can serve as an indicator of disease activity when elevated 1
- Joint aspiration with synovial fluid analysis should be performed if infection cannot be excluded clinically, particularly with unilateral involvement 3