Background/Purpose: Spinal X-rays are considered as gold standard for assessing structural damage in the spine in AS, and a scoring system, the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) is the preferred assessment method. In clinical studies and therapeutic trials, the mSASSS scoring process is usually done by ≥1 trained readers. In daily practice, the ability of rheumatologists and radiologists to adequately use the mSASSS without a specific training is unknown. In addition, it is not known what the impact would be in studies when using the score of multiple readers in various centres as in daily practice, instead of using a centralized scoring with a few trained readers. Therefore we want to compare the results of the mSASSS of the local reading of baseline spinal X-Rays to the centralized reading as the gold standard.

Methods: Patients aged 18-50 with recent chronic back pain (≥3 months, ≤3 years) from 25 participating centers in France were included in the DESIR (Devenir des Spondylarthropathies Indifferenciées Récentes) -cohort (n=708). All available baseline X-rays of cervical and lumbar spine were scored by the local radiologist/rheumatologist who might have access to clinical data, according to the mSASSS scoring method. In addition, 2 well-calibrated centralized readers independently scored the same X-rays, blinded for any other data. In case the centralized readers disagreed, an experienced radiologist served as adjudicator. Agreement between the 2 centralized readers, and between the local and centralized scores was calculated (Kappa; percentage agreement). To calculate the agreement between readers a cut-off of ≥1 for mSASSS was used. When comparing centralized readers with local readers the mSASSS of the centralized readers was combined.

Results: Patients with complete X- ray data (n=664) were included in these analyses. The large majority of patients had a normal mSASSS both scored by the central and local readers. The agreement between the 2 centralized readers was 89.3% with a kappa of 0.50 (see table). Comparing the local readings with the centralized scores there was an agreement in 72.2% of the cases with a kappa of 0.19. The local readers scored an mSASSS ≥1 in 169 cases, while this was in 119 cases if scored by central readers.

Conclusion: The agreement between two trained central readers is better than between central and local readers. Local readers overestimate damage in the spine in comparison to the gold standard of central reading.

		Reader 2
Reader 1		mSASSS ≥1	mSASSS <1
	mSASSS ≥1	45	29
	mSASSS <1	42	548
	Kappa = 0.50 / Agreement = 89.3%
		Centralized score (2/3)
Local score		mSASSS ≥1	mSASSS <1
	mSASSS ≥1	52	117
	mSASSS <1	67	427
	Kappa = 0.19 / Agreement = 72.2%

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/how-reliable-is-the-scoring-of-msasss-in-clinical-practice-in-centers-participating-in-desir-comparison-with-the-gold-standard-central-reading/