Objective: The assessment of inflammation activity in ulcerative colitis (UC) includes endoscopy and histology. Confocal laser endomicroscopy (CLE) combines real-time endoscopy and histology. This study was aimed at evaluating the application of CLE in the assessment of inflammation activity in UC.

Methods: In total, 73 consecutive patients with UC who visited Qilu Hospital for colonoscopy surveillance underwent CLE. Inflammation activity was first assessed by the colonoscopy Baron score, then by CLE with a 4-grade classification of crypt architecture, as well as by analysis of microvascular alterations and fluorescein leakage. Targeted biopsy samples were taken for histological analysis. Stored CLE images were subjected to post-CLE objective assessment.

Results: Both assessment of crypt architecture and fluorescein leakage with CLE showed good correlations with histological results (Spearman's rho, both P<0.001). CLE seemed to be more accurate than conventional white-light endoscopy for evaluating macroscopical normal mucosa. More than half of the patients with normal mucosa seen on conventional white-light endoscopy showed acute inflammation on histology, whereas no patients with normal mucosa or with chronic inflammation seen on CLE showed acute inflammation on histology. Assessment of microvascular alterations by CLE showed good correlation with histological findings (P<0.001). On post-CLE objective assessment, subjective architectural classifications were supported by the number of crypts per image (P<0.001) but not fluorescein leakage results by gray scale (P=0.194).

Conclusions: CLE is reliable for real-time assessment of inflammation activity in UC. Crypt architecture, microvascular alterations, and fluorescein leakage are promising markers in CLE evaluation.