Evidence-based correlation between anti-streptolysin O serum titer and sacroiliac joint disorder.

Objective: Poststreptococcal reactive arthritis (PSReA) is a nonsuppurative sequela of antecedent streptococcal infection, and can be investigated when detecting the anti-streptolysin O (ASO) titer. The relationship between ASO titer and involvement of the peripheral synovial joints has been examined in PSRA, but data are sparse for the sacroiliac (SI) joint. Quantitative SI joint scintigraphy has been used clinically to detect active SI joint disorders, but not for PSReA.

Methods: A total of 84 subjects were recruited; mean age at enrollment was 23 years (range 18.0-36.4 yrs). All subjects were examined for ASO titer levels (range 25-520 IU/ml) and SI joint imaging, determined by sacroiliac to sacrum (SI/S) ratio derived from SI scintigraphy.

Results: Most of the subjects with high ASO titer had unclassified or undifferentiated arthritis. Good correlation between the ASO titer and the SI/S ratio was determined statistically using Pearson correlation coefficients. The relationships between ASO titer and SI/S ratio at various locations (laterality: left, right; location of part: upper, middle, lower) were found to be significantly correlated using generalized estimating equations. After adjustment for potential confounders, a highly significant association was determined between ASO titer and SI/S ratio (p < 0.0001), with an increase of 1 IU/ml of titer resulting in a significant increase in SI/S ratio by 0.0008 units. Age was significantly associated with SI/S ratio (p = 0.0022), with each extra year increasing the ratio by 0.0074.

Conclusion: Our findings demonstrate a high correlation between SI joint involvement and high ASO titers. Subjects with SI joint involvement should be advised to have an ASO titer examination and quantitative SI joint scintigraphy.