Efficacy and safety of methylene blue injection for intractable idiopathic pruritus ani: a single-arm metaanalysis and systematic review

Purpose: To evaluate how effective methylene blue injection was at treating intractable idiopathic pruritus ani.

Methods: A comprehensive literature search of the PubMed, Embase, Cochrane library, and Web of Science databases was conducted. All clinical studies (prospective and retrospective) that evaluated the efficacy of methylene blue in treating intractable idiopathic pruritus ani were included. Studies that reported the resolution rate, after a single injection and after a second injection, the recurrence rate, symptom scores, and transient complications of methylene blue injections in treating intractable idiopathic pruritus ani were included.

Results: The seven selected studies included 225 patients with idiopathic pruritus ani. The resolution rates after a single injection and after a second injection was 0.761 (0.649-0.873, P < 0.01, I² = 69.06%) and 0.854 (0.752-0.955, P < 0.01, I² = 77.391%), respectively, the remission rates at 1, 3, and 5 years were 0.753 (0.612-0.893, P < 0.001), 0.773 (0.675-0.871, P < 0.001) and 0.240 (0.033-0.447, P < 0.001), respectively, the effect value of the merger was 0.569 (0.367-0.772, P < 0.001, I² = 79.199%), and the recurrence rates at 1, 2, 3, and < 1 year were 0.202 (0.083-0.322, P < 0.001), 0.533 (0.285-0.781, P < 0.001), 0.437 (-0.044, 0.917, P < 0.001) and 0.067 (0.023-0.111, P < 0.001), respectively. The effect value of the merger was 0.223 (0.126-0.319, P < 0.001, I² = 75.840).

Conclusion: Using methylene blue injections to treat intractable idiopathic pruritus ani is relatively efficacious, resulting in a relatively low recurrence rate and no severe complications. However, the available literature was of poor quality. Therefore, higher quality studies are necessary to confirm that methylene blue injection is efficacious for pruritus ani, such as a randomized prospective multicenter studies.