Erosive arthritis has a broad differential:
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clinically an acute inflammatory attacks (swelling, erythema, pain) in postmenopausal women
typically the interphalangeal joints, 1st carpometacarpal joint 6, but not the metacarpophalangeal (MCP) joints and large joints
classic central erosions (gull-wing appearance); possible ankylosis
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sometimes rheumatoid factor (RF) positive
usually proximal, bilateral and symmetric involvement: metacarpophalangeal joints, proximal interphalangeal joints, and carpal bones; involves the hands before the feet
erosions in "bare area", frequently in metacarpophalangeal joints 2
periarticular osteopenia and later osteoporosis (both unlike psoriatic arthritis), uniform joint space narrowing, subchondral cyst formation, and subluxations; no new bone formation unlike psoriatic arthritis and reactive arthritis
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commonly involves the hands and there is an interphalangeal predominant distribution in psoriatic arthritis vs. metacarpophalangeal joint predominance in rheumatoid arthritis
new bone formation key, not a feature of rheumatoid arthritis 2
affects the synovioentheseal complex, explaining enthesitis, adjacent joint capsule synovitis, and periarticular inflammation 2
erosions; classic: "pencil in cup"; osteoporosis is not a feature in psoriatic arthritis
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predilection for the lower limb
symmetrical involvement of the proximal interphalangeal joints, metacarpophalangeal joints, and carpal bones.
osteopenia and then osteoporosis, uniform joint space loss, subchondral cyst formation, subluxations, marginal erosions.
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erosions with overhanging edges (rat bite erosions)
tophi, most commonly involving the 1st metatarsophalangeal joint, known as podagra
pressure erosion (e.g. tenosynovial giant cell tumors, synovial osteochondromatosis)
articular defects simulating erosions in CPPD, osteonecrosis, osteochondritis dissecans, and osteochondral fractures
septic arthritis: mono-articular