Features		Ankylosing spondylitis	Reactive arthritis (including Reiter’s syndrome)	Psoriatic arthritis	IBD-associated spondyloarthropathy
Prevalence		0.1% to 0.2%	0.1%	0.2% to 0.4%	Rare
Age at onset		Late teens to early adulthood	Late teens to early adulthood	35 to 45 years	Any age
Male-to-female ratio		3:1	5:1	1:1	1:1
HLA-B27		90% to 95%	80%	40%	30%
Sacroiliitis
	Frequency	100%	40% to 60%	40%	20%
	Distribution	Symmetric	Asymmetric	Asymmetric	Symmetric
Syndesmophytes		Delicate, marginal	Bulky, nonmarginal	Bulky, nonmarginal	Delicate, marginal
Peripheral arthritis
	Frequency	Occasional	Common	Common	Common
	Distribution	Asymmetric, lower limbs	Asymmetric, lower limbs	Asymmetric, any joint	Asymmetric, lower limbs
Enthesitis		Common	Very common	Very common	Occasional
Dactylitis		Uncommon	Common	Common	Uncommon
Skin lesions		None	Circinate balanitis, keratoderma blennorrhagicum	Psoriasis	Erythema nodosum, pyoderma gangrenosum
Nail changes		None	Onycholysis	Pitting, onycholysis	Clubbing
Ocular conditions		Acute anterior uveitis	Acute anterior uveitis, conjunctivitis	Chronic uveitis	Chronic uveitis
Oral conditions		Ulcers	Ulcers	Ulcers	Ulcers
Cardiac conditions		Aortic regurgitation, conduction defects	Aortic regurgitation, conduction defects	Aortic regurgitation, conduction defects	Aortic regurgitation
Pulmonary features		Upper lobe fibrosis	None	None	None
Gastrointestinal conditions		None	Diarrhea	None	Crohn’s disease, ulcerative colitis
Renal conditions		Amyloidosis, IgA nephropathy	Amyloidosis	Amyloidosis	Nephrolithiasis
Genitourinary conditions		Prostatitis	Urethritis, cervicitis	None	None