International Consensus on ANA Patterns (ICAP) Classification Tree Revisited: A Single Centre Report on Four Nuclear Patterns from a Tertiary Care Centre in India.

Background: ICAP describes ANA patterns from AC- 0 to AC-29. They are further marked for competent or expertise reporting depending on ease of identification. There are some debatable patterns in ICAP which share similar features with a few others yet have a distinct identity and few others which are not addressed by ICAP but are described by BCA like Quasihomogenous. This study analysed four nuclear patterns with overlapping features, namely Homogenous, speckled, Dense Fine Speckled70(DFS70) and quasi-homogenous to identify challenges posed in their identification due to overlapping features.

Methods: All samples which were reported as positive for the above four nuclear patterns (n=388) by IIF using HEp-2 cell were included in the study. LIA was performed on 103 such samples to look for association between the ANA patterns and specific antibody detected by LIA.

Results: DFS70 pattern is a rare pattern and existed in combination with other autoantibodies thus making its identification difficult on IIF. Homogenous pattern corresponded to AC- 29 (anti-topoisomerase, anti-Scl 70) which was probably due to wrong identification. Mixed pattern i.e speckled and homogenous was associated with Sm and U1sn RNP antibodies.

Conclusions: DFS 70 is a pattern with overlapping features of both homogenous and speckled and calls for expertise reporting. More awareness is required about AC 29 pattern as it is an overlap of five different components. Its identification poses significant challenges and is rightly placed in the expert reporting by ICAP. Mixed pattern (speckled and homogenous) referred to as Quasihomogenous by BCA needs to be addressed by ICAP.