Factors Associated with Pain During Transperineal Prostate Fusion Biopsy Under Local Anaesthesia: A Prospective Study

Background/Objectives: Transperineal MRI-fusion prostate biopsy under local anaesthesia is increasingly performed in the outpatient setting, which places greater weight on procedural tolerability. Psychological and anatomical determinants of pain have rarely been compared within a single model, and MRI-derived perineal anatomical parameters have not been evaluated. We aimed to identify factors associated with procedural pain and to determine at which step pain peaks. Methods: In this prospective, pre-registered, single-centre cohort study (OSF: osf.io/pbacu), 182 consecutive men referred for transperineal MRI-ultrasound fusion biopsy under local anaesthesia were assessed for eligibility, and 177 constituted the Full Analysis Set. State anxiety was measured with the STAI-S before and after biopsy. Pain was rated on a Numeric Rating Scale (NRS 0-10) by a nurse not involved in the procedure at four predefined steps: probe insertion, skin infiltration, periprostatic nerve block and core sampling. Midline perineal tissue thickness (MPT) and levator ani thickness were measured on pre-biopsy T2-weighted MRI by a radiologist blinded to outcomes. The primary outcome was the maximum NRS score; ten candidate predictors were entered simultaneously into a multivariable linear regression model. Results: Clinically significant pain (maximum NRS score ≥ 4) was reported by 157 of 177 men (88.7%). Pain differed markedly across steps (F(2.68, 472.39) = 230.51, p < 0.001, partial η² = 0.567) and peaked at the periprostatic nerve block (5.88 ± 2.03), exceeding core sampling by 2.62 points (95% CI 1.85-3.40). In multivariable analysis (R² = 0.192), pre-biopsy anxiety was the strongest independent predictor (standardised β = 0.30, partial R² = 0.094, p < 0.001), followed by prostate volume (β = 0.19, p = 0.014); MPT showed only an exploratory, borderline association (β = 0.17, p = 0.052). Core number, body mass index and levator ani thickness were not associated with pain. Conclusions: Most men undergoing transperineal MRI-fusion biopsy experience clinically significant pain, peaking at administration of the periprostatic block rather than at core sampling. Pre-procedural anxiety and prostate volume, both available beforehand, support simple risk stratification, while the block itself is the most logical target for analgesic improvement.