Table 1.

Differences Between Ankylosing Spondylitis and Diffuse Idiopathic Hyperostosis in Relation to Prevalence, Age, Etiology, and Diagnosis.

	Ankylosing Spondylitis	Diffuse Idiopathic Hyperostosis
Prevalence	0.1% to 1.4%1	Estimated at between 2.9% and 25%8–10
Age	Onset in second and third decades of life1	Peak between 60 and 69 years8
Etiology	Inflammatory rheumatic disorder, genetic interaction (HLA-B27), environmental factors18–21	Associations with obesity, type 2 diabetes mellitus, and advanced age, noninflammatory12,13
Diagnosis	Inflammatory changes confirmed by imaging (magnetic resonance imaging, radiography) (typically sacroiliac joints, axial spine, ie, “bamboo spine,” enthesitis) and clinical symptoms (morning stiffness, back/buttock pain), elevated inflammatory parameters, acute anterior uveitis92–94	Bridged ossification of the anterior longitudinal ligament over at least 4 consecutive segments on conventional radiography15,16