Which of the following is a characteristic finding of Rheumatoid Arthritis?
Other conditions
Arthritic disorders
No
U
A
Answer choice "A" represents a classic radiographic finding of Rheumatoid Arthritis (RA). Ivory phalanx is a radiographic finding that is very specific for Psoriatic Arthritis (PsA). A finding of B. burgdorferi within a synovial culture would indicate a diagnosis of Lyme disease. Urethritis and conjunctivitis are symptoms common to Reactive Arthritis.
Exam / Radiographic Findings (see Jacobson et al below - free link):
Rheumatoid Arthritis = Swan-neck deformity (hyperextension PIP; flexion DIP); XR = deformity common bilateral/symmetrical, 5th MT head lateral erosions often first site of radiographic changes (even before hand/wrist changes), MTP/IPJ joint narrowing; C1-C2 spinal involvement (neck XR prior to OR)
Psoriatic Arthritis = Dactylitis (isolated digit swelling); XR = joint inflammation, bone proliferation, periostitis, enthesitis; distal joint distribution. Ivory phalanx is the increased radiodensity of an entire phalanx as a result of periostitis/endosteal bone formation. Pencil-in-cup deformity is the appearance of bony erosions/resorption of a distal bone sitting in the proximal bone, giving the appearance of a pencil in a cup (most commonly seen in PsA but can be a finding in RA, systemic sclerosis, and reactive arthritis).
Reactive Arthritis = joint inflammation, bone proliferation, periostitis, enthesitis. This is similar to PsA, so clinical history, patient age/sex, and joint distribution will help work through your differential).
Citation:
Scott DL. Radiological progression in established rheumatoid arthritis. J Rheumatol 2004; 31(Suppl 69): 55-65.
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