Table 2.

Summary of the follow-up studies

Ref.	Sample size (M/F)	Mean age (yr)	Menopausal status (pre:post)	Disease duration (yr)	Dexa machine	Dexa site (coefficient variation %)	Follow-up (mo)	Outcome	Conclusion
Lee et al[17]	AS: 14 (14/0) 7 early AS 7 advanced AS	33.3 54.6	NA	5.4 27	Hologic	LS (1), FN (1)	15	Baseline LS BMD measured by QCT decrease in both early (also by DXA) and advanced diseases and do not change significantly over 15 mo HLA-B27 92.9%	AP LS DXA in late AS is less useful than QCT in determining the degree of osteopenia in late AS
Gratacós et al[6]	AS: 34 (27/7) Active 14 (12/2) Inactive 20 (15/5)	Active: 33 Inactive: 31	7:0	7.5 5.3	Lunar	LS (0.8), FN (2.3)	19	At the end of the follow-up period, patients with active AS show a significant reduction in bone mass in the LS (5%) and FN (3%)	Loss of bone mass only in patients with persistent active AS suggests that inflammatory activity plays a major role in the pathophysiology of the early bone loss
Maillefert et al[32]	AS: 54 (35/19)	37.3	16:3	12.4	Hologic	PA L2-4 (2.8), left FN (4)	24	After 2 yr, BMD did not change at the LS and decreased at the FN The change in BMD at FN was related to persistent systemic inflammation HLA-B27 88.9% VF: 3.7% after 24 mo	Persistent inflammation may be an etiologic factor of bone loss in AS
Kaya et al[31]	AS: 55 (42/13) Active: 22 Inactive: 33	35.8	13:0	11.1	Lunar	AP L2-4 (2.1), PF (2.3)	24	Active AS have lower BMD at PF than inactive ones but LS BMD was similar 0.9% decrease in BMD at FN and increase at LS after follow-up, this change not different in active and inactive AS Active AS OP: PF: 22.7%, LS: 27.3% Osteopenia: PF: 40.9%, LS: 31.8 inactive AS OP; PF: 3%, LS: 21,2% Osteopenia; PF 45.5%, LS: 33.3%	PF measurements seem to be less affected from disease-related new bone formation
Haugeberg et al[33]	SpA: 30 (15/15)	31.1	15:0	6	Lunar	AP L2-4 (2.3), both hip (2.8) and hand (1.1)	12	No significant reduction in BMD at hip, spine and hand is seen after 12 mo follow-up Bone loss at PF is found to be associated with raised baseline CRP levels, baseline BMO of the SIJs on MRI HLA-B27 56.7	Bone loss in patients with SpA is a result of systemic inflammation and starts early in the disease process
Korkosz et al[18]	AS: 19 (19/0)	45.6	NA	16.5	Lunar	L2-4 (1.6-2.2), left hip QCT: L1-5	120	During the follow-up VF: 15.8% In spine, trabecular BMC decrease by QCT whereas BMD increase by DXA	In AS patients, spinal trabecular bone density evaluated by QCT decrease over 10-yr follow-up and it is not related to baseline radiological severity of spinal involvement

AP: Anteroposterior; AS: Ankylosing spondylitis; BMC: Bone mineral content; BMD: Bone mineral density; BMO: Bone marrow edema; DXA: Dual energy X-ray absorptiometry; F: Female; FN: Femur neck; HLA: Human leukocyte antigen; LS: Lumbar spine; M: Male; MRI: Magnetic resonance imaging; NA: Not applicable; NM: Not mentioned; OP: Osteoporosis; PA: Posteroanterior; PF: Proximal femur; QCT: Quantitative computed tomography; SIJs: Sacroiliac joints; VF: Vertebra fracture.