Comparison of features of musculoskeletal disease in systemic lupus erythematosus or rheumatoid arthritis

Feature	Systemic lupus erythematosus	Rheumatoid arthritis
Arthralgia	Common	Common
Arthritis	Common	Deforming
Symmetry	Yes	Yes
Joints involved	PIP>MCP>wrist>knee	PIP+MCP>wrist>knee
Synovial hypertrophy	Rare	Common
Synovial membrane abnormality	Minimal	Proliferative
Synovial fluid	Transudate	Exudate
Subcutaneous nodules	Rare	35%
Erosions	Very rare	Common
Morning stiffness	Minutes	Hours
Myalgia	Common	Common
Myositis	Rare	Uncommon
Osteoporosis	Variable	Common
Avascular necrosis	5 to 50%	Uncommon
Deforming arthritis	Uncommon	Common
Swan neck	10%, reducible	Common, not reducible
Ulnar deviation	5%, reducible	Common, not reducible

PIP: proximal interphalangeal; MCP: metacarpophalangeal.

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