Introduction

While trans-perineal ultrasound (TPUS) is promising, its accuracy compared to trans-abdominal ultrasound (TAS) and endoscopic ultrasound (EUS) in predicting rectal histoendoscopic activity in ulcerative colitis (UC) is unclear.

Aims & Methods

We aimed to evaluate the reliability of TPUS in predicting rectal histoendoscopic activity in UC using EUS as the reference standard. This prospective study included adult UC patients who underwent TAS and TPUS, followed by EUS. Rectal total wall thickness (TWT) and vascularity (Modified Limberg Score, MLS) were measured on all modalities. Additionally, mucosal thickness (MT) and submucosal thickness (SMT) were assessed on EUS. Receiver operating characteristic (ROC) analysis was performed to determine the area under the curve (AUC) for predicting endoscopic activity (Ulcerative Colitis Endoscopic Index of Severity, UCEIS >1) and histologic activity (Nancy Index >1).

Results

A total of 142 UC patients (33.8% female, median age 40 years, BMI 22.5 kg/m²) were included. Disease extent was proctitis (12%), proctosigmoiditis (58%), and extensive colitis (30%). The median SCCAI score was 3 (range: 0-8). Most patients were on 5-ASA (90.8%), azathioprine (31%), and tofacitinib (10.6%).
The median rectal length visualized on TPUS was 3.9 cm (2.4-6.3 cm). Endoscopic remission (UCEIS ≤1) was observed in 49.3% of patients, and histologic remission (NHI ≤1) in 38.7%.
For endoscopic activity, EUS had the highest accuracy, with MT >0.95 mm (AUC: 0.96, sensitivity: 98.6%, specificity: 87%) and MLS >1 (AUC: 0.95, sensitivity: 81.7%, specificity: 94%). TPUS had moderate accuracy(TWT >5.4 mm, AUC: 0.73), while TAS performed poorly (TWT >5.8 mm, AUC: 0.63).
For histologic remission, EUS vascularity (MLS >1) was most predictive (AUC: 0.91, sensitivity: 66.3%, specificity: 98.1%), followed by rectal TWT ≥4 mm (AUC: 0.83) and MT ≥0.95 mm (AUC: 0.86). Among non-EUS techniques, TPUS (TWT ≥6.1 mm, AUC: 0.66) showed moderate accuracy, while TAS was the least predictive (AUC: 0.62).
The Milan Ultrasound Criteria (MUC) demonstrated highest accuracy for endoscopic remission with EUS MUC ≥8 (AUC: 0.94), followed by TPUS (AUC: 0.78) and TAS (AUC: 0.67). For histologic remission, EUS MUC >7 had the highest accuracy (AUC: 0.87), followed by TPUS (MUC ≥9.7, AUC: 0.70) and TAS (AUC: 0.64) (Table 1). BMI-based comparisons showed no significant differences in MUC scores.

Measure	Sensitivity	Specificity	AUC	p-value	95% CI
	Endoscopic Activity
TAS (MUC) (≥8.5)	67.6%	60.9%	0.67	<0.001	0.59-0.76
TPUS (MUC) (≥8)	86%	62.3%	0.78	<0.001	0.70-0.86
EUS (MUC) (≥8)	81.7%	81.2%	0.94	<0.001	0.85-0.95
	Histologic activity
TAS (MUC) (>8.6)	62.8%	66%	0.64	0.005	0.54-0.74
TPUS (MUC) (≥9.7)	59.3%	79.6%	0.70	<0.001	0.61-0.79
EUS (MUC) (>7)	83.7%	81.5%	0.87	<0.001	0.81-0.93

Correlation analysis showed a strong correlation between TPUS and EUS TWT (r=0.371, p<0.001). TPUS and TAS had moderate correlation (r=0.309, p<0.001), while TAS and EUS showed weaker correlation (r=0.264, p=0.002 for average TWT, r=0.234, p=0.005 for lower rectal TWT). MUC scores correlated best between EUS and TPUS (r=0.425, p<0.001).

Conclusion

While EUS remains the most accurate, TPUS shows moderate accuracy for assessing rectal inflammation in UC. However, TPUS is limited to the lower rectum and needs further validation for better reproducibility. Standardized cutoffs and integration into routine UC monitoring could enhance non-invasive assessment, reducing endoscopy reliance and improving patient management.(NCT06717906).

References

1. Sagami S, Kobayashi T, Aihara K, Umeda M, Morikubo H, Matsubayashi M, Kiyohara H, Nakano M, Ohbu M, Hibi T. Transperineal ultrasound predicts endoscopic and histological healing in ulcerative colitis. Aliment Pharmacol Ther. 2020;51(12):1373-1383. [10.1111/apt.15767]
2. Sagami S, Kobayashi T, Aihara K, Umeda M, Odajima K, Morikubo H, Asonuma K, Miyatani Y, Fukuda T, Matsubayashi M, Kiyohara H, Nakano M, Hibi T. Early improvement in bowel wall thickness on transperineal ultrasonography predicts treatment success in active ulcerative colitis. Aliment Pharmacol Ther. 2022;55(10):1320-1329. [10.1111/apt.16817]