Does evaluation of the ligamentous compartment enhance diagnostic utility of sacroiliac joint MRI in axial spondyloarthritis?

Table 1 Demographical and clinical characteristics of two spondyloarthritis inception cohorts, and percentage of subjects with bone marrow edema or fat metaplasia in the cartilaginous and ligamentous compartments of the sacroiliac joints (mean percentage over five readers)

Cohort	A (n = 89)				B (n = 88)
Recruitment mode	Suspected axial SpA by practising rheumatologists or PCP				AAU plus past or present back pain
Group	nr-axSpA	AS	NSBP	HC	nr-axSpA	AS	NSBP
Number of subjects	20	10	39	20	31	24	33
Male:female (% male)	11:9 (55.0)	8:2 (80.0)	11:28 (28.2)	7:13 (35.0)	17:14 (54.8)	11:13 (45.8)	17:16 (51.5)
Age (years)	32.2 (12.3)	30.0 (9.5)*	32.7 (11.5)	30.6 (6.5)	36.2 (12.1)	41.5 (7.1)*	33.6 (15.7)
Symptom duration (years)	1.3 (1.8)*	3.9 (1.8)*	NA	NA	10.0 (14.0)*	12.5 (13.5)*	NA
HLA B27 positive (%)	12 (60.0)	9 (90.0)	ND	ND	24 (80.0)^b	21 (87.5)	10 (55.6)^b
BASDAI (NRS)	4.4 (3.1)^a	5.4 (1.5)^a	NA	NA	3.5 (4.4)	2.0 (3.4)^b	NA
BASFI (NRS)	1.8 (3.9)*^a	2.7 (1.5)^a	NA	NA	0.8 (2.3)*	0.6 (2.8)^b	NA
CRP (mg/l)	4.0 (4.5)^a	5.0 (8.0)^a	ND	ND	2.7 (5.2)	8.0 (8.7)^b	0.9 (0.9)^b
BME cart	83.0	88.0	27.7	34.0	45.2	74.2	27.9
BME lig	42.0	80.0	3.6	6.0	11.6	38.3	2.4
Fat cart	47.0	66.0	29.2	18.0	43.9	79.2	22.4
Fat lig	21.0	46.0	17.9	12.0	25.2	42.5	9.1

Values for patient characteristics are the median (interquartile range; expressed as difference between first and third quartile) unless otherwise stated
*P ≤ 0.05 (Fisher’s exact test) between cohorts A and B
^aCohort A: CRP values are based on 18, and BASDAI/BASFI values on 19 patients with nr-axSpA, respectively; BASDAI/BASFI and CRP values are based on 9 patients with AS
^bCohort B: HLA B27 values are based on 30 patients with nr-axSpA; BASDAI/BASFI and CRP values are based on 22 patients with AS; in NSBP patients, HLA B27 and CRP values are based on 18 subjects; the prevalence of HLA B27 in patients with AAU in general is 50–60 % [41]
AAU Acute anterior uveitis, AS Ankylosing spondylitis, BASDAI Bath Ankylosing Spondylitis Disease Activity Index, BASFI Bath Ankylosing Spondylitis Functional Index, BME Bone marrow edema, Cart Cartilaginous compartment of the sacroiliac joint, CRP C-reactive protein (reference range ≤5 mg/l), Fat Fat metaplasia, HC Healthy control, HLA B27 Human leucocyte antigen B27, Lig Ligamentous compartment of the sacroiliac joint, NA Not applicable, ND Not done, nr-axSpA Nonradiographic axial spondyloarthritis, NRS Numeric rating scale, NSBP Nonspecific back pain, PCP Primary care physician

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