Rheumatoid Arthritis Diagnosis: Key Clinical Signs

The presence of specific deformities in the hands and the development of Baker's cysts are highly suggestive of Rheumatoid Arthritis (RA).

Recognizing Rheumatoid Arthritis Manifestations

• Swan-neck deformity: Characterized by hyperextension of the distal interphalangeal (DIP) joint and flexion of the proximal interphalangeal (PIP) joint. This is a common consequence of inflammation and laxity in RA.
• Buttonhole deformity (Boutonnière deformity): Involves flexion of the PIP joint and hyperextension of the DIP joint, caused by damage to the central slip of the extensor tendon.
• 'Z' deformity of the thumb: This deformity results from instability at the carpometacarpal (CMC) and metacarpophalangeal (MCP) joints, causing flexion at the MCP and thumb adduction.
• Baker's cysts: These are fluid-filled sacs that develop at the back of the knee (popliteal fossa). They are a common extra-articular manifestation of RA due to increased synovial fluid production in the knee joint.

While other conditions like Reiter's syndrome, gouty arthritis, and psoriatic arthritis cause joint inflammation, the specific combination of 'swan-neck' deformity, 'buttonhole' deformity, 'Z' deformity of the thumb, and Baker's cysts is most characteristic of Rheumatoid Arthritis.

Conclusion

Based on the characteristic clinical signs presented, the condition is Rheumatoid Arthritis.