Can rheumatoid arthritis in one joint cause rheumatoid arthritis in another joint?

Rheumatoid Arthritis Does Not "Cause" Spread from One Joint to Another—It Is a Systemic Autoimmune Disease

Rheumatoid arthritis is fundamentally a systemic autoimmune disease, not a condition where inflammation in one joint directly causes disease in another joint. The involvement of multiple joints reflects the underlying systemic immune dysregulation, not a local spreading mechanism from joint to joint.

Understanding RA as a Systemic Disease

The pathophysiology of RA involves systemic immune activation where HLA-DRB1 alleles present citrullinated peptides to T cells throughout the body, initiating a widespread autoimmune cascade rather than a localized process. 1 This means:

• B cell activation produces rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) systemically, forming immune complexes that circulate throughout the bloodstream 1
• The inflammatory process targets synovial tissue in multiple joints simultaneously based on systemic immune dysregulation, not sequential spread 2, 3
• Morning stiffness lasting ≥1 hour reflects the significant systemic inflammatory burden, not localized joint-to-joint transmission 1

Clinical Pattern of Joint Involvement

RA characteristically presents with symmetric polyarticular involvement, meaning multiple joints become affected as part of the disease process itself, not because one joint "infects" another. 4

The typical pattern includes:

• Small joints of hands and feet (MCPs, PIPs, 2nd-5th MTPs, thumb IPs, wrists) are preferentially targeted by the autoimmune process 1, 4
• Symmetric involvement is the hallmark—both hands, both feet—which would not occur if this were a spreading mechanism 4
• The likelihood of RA diagnosis increases with the number of small joints involved, reflecting the systemic nature of autoimmune targeting 2

Progressive Joint Involvement Over Time

While RA doesn't spread from joint to joint like an infection, additional joints can become involved over the disease course:

• This represents progression of the underlying systemic autoimmune disease, not transmission between joints 3, 5
• Untreated or inadequately treated RA leads to ongoing immune activation that can recruit additional joints into the inflammatory process 6, 3
• Early treatment with disease-modifying antirheumatic drugs (DMARDs) prevents this progression by controlling the systemic immune dysregulation 6, 3

Critical Clinical Implications

Early diagnosis and immediate treatment are essential because they address the systemic immune process before additional joints become damaged. 6, 3

• EULAR recommends treatment begin immediately after RA diagnosis to prevent disease progression 6
• Methotrexate as first-line therapy targets the systemic immune dysfunction, not individual joints 6
• The treatment target should be sustained remission or low disease activity, which prevents new joint involvement by controlling systemic inflammation 6
• Frequent monitoring (every 1-3 months in active disease) allows adjustment of systemic therapy before additional joints are affected 6

Common Pitfall to Avoid

Do not conceptualize RA as a localized joint problem that spreads mechanically or through direct contact between joints. This misunderstanding can lead to:

• Delayed systemic treatment while focusing on individual symptomatic joints 3
• Failure to recognize that controlling systemic inflammation is the only way to prevent additional joint involvement 6, 5
• Inadequate appreciation that extra-articular manifestations (lungs, heart, eyes) arise from the same systemic process, not from joint involvement 3