Table 1.

Differentiating rheumatoid arthritis (RA) and psoriatic arthritis (PsA)

Features	PsA	RA
Number of joints involved	30–50% with oligoarthritis	Predominant polyarthritis
Joint involvement	Any joint, including distal interphalangeal joints	Usually distal interphalangeal joint sparing
Enthesitis	Typical, clinically present in 60–80%	Not typical
Dactylitis	Present in 30%	Not typical
Axial involvement	Axial spondyloarthritis phenotype	Erosive cervical disease
Skin/nail disease	Psoriasis in 80%, nail disease in 60%	Background population risk or lower
Serology	Usually RF and CCP negative	Usually RF and/or CCP positive
Typical radiographic changes	Periosteal new bone formation (uncommon especially in early disease)	Erosion and osteopenia

CCP = cyclic citrullinated peptide; RF = rheumatoid factor