Procedural Optimization of Capsaicin 8% Patch Therapy Using Ultrasound-Guided Bilateral Ankle Nerve Block in Painful Diabetic Peripheral Neuropathy: A Retrospective Comparative Cohort Study

Background: Application of the capsaicin 8% patch is commonly associated with treatment-related burning pain, which may necessitate rescue analgesia, compromise completion of the standardized 60 min application, and reduce acceptance of repeat treatment. Although capsaicin is an established therapy for painful diabetic peripheral neuropathy (PDPN), evidence supporting strategies to improve procedural tolerability remains limited. This study evaluated whether ultrasound-guided bilateral ankle nerve block (UGBANB) was associated with better procedural outcomes than topical eutectic mixture of lidocaine/prilocaine (EMLA) pretreatment or no pretreatment. Methods: This retrospective comparative cohort study included 90 adults with neurologist-confirmed PDPN who underwent capsaicin 8% patch therapy. Patients received no pretreatment (n = 30), topical EMLA pretreatment (n = 30), or UGBANB (n = 30). The primary outcome was cumulative procedural pain burden, quantified as the area under the Numeric Pain Rating Scale–time curve (AUC-NPRS) during the standardized 60 min application. Secondary outcomes included rescue tramadol requirements, treatment completion, early postprocedural pain intensity, procedural tolerability, willingness to undergo repeat treatment, and safety. Results: Cumulative procedural pain burden differed significantly among the three pretreatment strategies (one-way ANOVA: F = 289.8, p < 0.001; η2 = 0.87). Mean AUC-NPRS was 481.5 ± 39.2 NPRS·min with no pretreatment, 429.2 ± 36.0 with topical EMLA, and 256.3 ± 38.4 with UGBANB, corresponding to approximately 47% and 40% lower cumulative pain burden with UGBANB than with no pretreatment and topical EMLA, respectively. No patient receiving UGBANB required intravenous rescue tramadol, compared with 60.0% receiving EMLA and 100.0% receiving no pretreatment (p < 0.001). Treatment completion was 100% with UGBANB, compared with 83.3% with EMLA and 73.3% with no pretreatment. UGBANB was also associated with lower early postprocedural pain, greater procedural tolerability, and greater willingness to undergo repeat treatment. No serious treatment- or block-related adverse events were observed during the available follow-up. Conclusions: UGBANB was associated with better procedural tolerability and treatment delivery during capsaicin 8% patch therapy than topical EMLA or no pretreatment in patients with PDPN. These findings relate specifically to procedural optimization and should not be interpreted as evidence that UGBANB enhances the intrinsic or long-term analgesic efficacy of capsaicin. Prospective multicenter randomized controlled trials are needed to confirm these associations and determine whether improved procedural tolerability translates into better long-term treatment adherence, clinical outcomes, health-related quality of life, safety, and cost-effectiveness.