Background/Purpose: Traditionally, radiographic imaging was used to describe morphological differences between various types of axial SpA (axSpA). MRI has advanced understanding of disease, enabled earlier diagnosis and visualization of structural changes, and facilitated the identification of non-radiographic axial SpA (nr-axSpA). The magnitude of the pathologic changes in the axial skeleton is used to quantify inflammatory and structural outcomes in clinical trials and treatment of patients with axSpA. Objectives: To examine the MRI morphology of sacroiliitis (SI) and vertebral corner lesions in primary axSpA (1º) patients vs. secondary axSpA (2º) patients with concomitant psoriasis.

Methods: This posthoc analysis was performed on data from patients with axSpA enrolled in the EMBARK trial (NCT01258738). Patients with no baseline MRI lesions were excluded. Symmetric and asymmetric SI, structural lesions, and corner inflammatory lesions were analyzed in 1º axSpA vs. 2º axSpA patients with psoriasis. Data were analyzed using one-way analysis of variance for continuous parameters, Fisher’s exact tests for categorical parameters, Fisher’s exact chi-square for small sample sizes, and parametric and non-parametric approaches for structural lesions.

Results: The baseline demographics and disease characteristics between the 122 patients with 1º axSpA and 19 with 2º axSpA were similar. Asymmetric sacroiliitis was seen in significantly fewer 1° (43%) vs. 2° (68%) axSpA patients. There were no differences in mean SpondyloArthritis Research Consortium of Canada (SPARCC) scores between 1° and 2° axSpA for any of the 4 SI joint (SIJ) quadrants. However, the lower iliac quadrants had the highest SPARCC SIJ score and the upper iliac quadrants had the lowest SPARCC SIJ scores. When analyzing the 4 spine quadrants (lower/upper anterior and lower/upper posterior), 1° patients had higher total SPARCC spine scores than 2° patients for all 4 quadrants at baseline (Table). Collapsing the 4 quadrants shows that 1° axSpA patients had higher SPARCC MRI of the entire spine (23 discovertebral units (DVU); mean=5.6) compared with 2° axSpA patients (mean=2.2).

Conclusion: We found 1° axSpA patients had more symmetric sacroiliitis and extensive spinal bone marrow edema compared with 2° axSpA patients. In addition, women appeared to have more asymmetric sacroiliitis. These data may help physicians accurately diagnose patients and decide best treatment options.  

Table:

Parameter	Total (n=141)	1° axSpA with			2° axSpA with			Overall p-value
		Symmetric sacroiliitis (n=63)	Asymmetric sacroiliitis (n=52)	Non-sacroiliitis (n=7)	Symmetric sacroiliitis (n=4)	Asymmetric sacroiliitis (n=13)	Non-sacroiliitis (n=2)
Age, y, mean (SD)	32.1 (7.4)	30.9 (6.8)	32.5 (7.8)	35.3 (7.3)	29.3 (7.9)	33.5 (6.2)	47.0 (2.8)	0.2132
Male, n (%)	92 (65.3)	46 (73.0)	27 (51.9)	4 (57.1)	4 (100)	9 (69.2)	2 (100)	0.0896
Symptom duration, y, mean (SD)	2.6 (1.9)	2.4 (2.2)	2.6 (1.5)	2.7 (1.6)	1.8 (1.5)	3.2 (1.6)	2.9 (1.6)	0.2944
SPARCC MRI SIJ score, mean (SD)	10.5 (9.9)	15.9 (10.4)	5.4 (5.1)	2.1 (0.2)	27.5 (10.2)	5.9 (4.1)	2.5 (0.7)	0.0007
Left SPARCC SIJ, mean (SD)	5.2 (6.0)	7.9 (6.1)	3.1 (5.3)	0.8 (0.3)	10.4 (7.4)	1.8 (2.1)	1.3 (0.4)	0.0004
Right SPARCC SIJ, mean (SD)	5.4 (6.2)	8.0 (7.0)	2.3 (2.5)	1.4 (0.2)	17.1 (6.3)	4.0 (5.0)	1.3 (0.4)	0.0542
SPARCC MRI 6 DVU spinal score, mean (SD)	4.7 (7.0)	6.5 (8.8)	3.8 (5.5)	2.4 (2.1)	1.6 (3.3)	2.7 (3.6)	0.8 (1.1)	0.0141
SPARCC MRI 23 DVU spinal score, mean (SD)	5.1 (8.9)	7.3 (11.8)	3.9 (5.6)	2.4 (2.1)	1.6 (3.3)	2.5 (3.2)	0.8 (1.1)	0.0180
Fat metaplasia, mean (SD)	0.5 (1.6)	0.3 (0.9)	0.9 (2.5)	0 (0)	0.3 (0.5)	0.7 (1.1)	0 (0)	0.6805
Erosions, mean (SD)	2.6 (3.5)	4.2 (4.0)	1.1 (2.0)	0.3 (0.4)	3.1 (1.8)	1.0 (1.9)	0 (0)	0.0002

 

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