Clinical significance of cytoplasmic discrete dots (AC-18) patterns in HEp-2 cell indirect Immunofluorescence: insights from a Taiwanese multicenter study.

Introduction: The clinical significance of autoantibodies with the cytoplasmic discrete dots pattern in HEp-2 cell indirect immunofluorescence assay (HEp-2 IFA), now classified as the anti-cell 18 (AC-18) pattern by International Consensus on Antinuclear Antibodies Patterns (ICAP), varies across cohorts, and remained underexplored.

Methods: We conducted a cross-sectional study on patients who underwent antinuclear antibody (ANA) testing via HEp-2 IFA at the Chang Gung Memorial Health System in Taiwan between January 2019 and September 2021. Among 7429 ANA-positive cases, 77 exhibited the AC-18 pattern and underwent chart review. A propensity score (PS) matching analysis was subsequently conducted, in which 53 patients exhibiting an isolated AC-18 pattern were matched to 265 control subjects, selected from a pool of 31,143 ANA-negative individuals at a 1:5 ratio. Matching was based on age, sex, and comorbidities.

Results: Among the 77 patients positive for AC-18 pattern, 14.3% had Sjögren disease (SjD), 11.7% had rheumatoid arthritis (RA), 5.2% had idiopathic inflammatory myopathy (IIM), and 3.9% had systemic lupus erythematosus (SLE). Specifically, 29.9% had various types of cancer. In PS matching model, the prevalence of SjD, IIM and cancer was significantly higher in patients with the AC-18 pattern compared to the control group, with odds ratios (OR) of 16.8 (95% CI 3.3, 85.7), 7.9 (95% CI 1.3, 48.4), and 4.8 (95% CI 2.3, 10.3), respectively.

Conclusions: Individuals with a positive ANA test showing the AC-18 pattern have a notably higher prevalence of cancer and autoimmune diseases compared to those with negative ANA results.