This is the first successful attempt at the meta-analysis of clinical trials on the use of electrical stimulation with non-implanted devices to treat post-stroke urinary incontinence.   The purpose of this study was to determine the effect of frequency of therapy sessions on the effect size of electrical stimulation with non-implanted devices on post-stroke urinary incontinence.

A study protocol was developed based on the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P)[1] and the Cochrane handbook for systematic review of interventions. The protocol was prospectively registered on PROSPERO (https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=74804). Searches were conducted in the MEDLINE (1966 to July 2020), EMBASE (1974 to July 2020), Cochrane Central Register of Controlled Trials (CENTRAL; 1966 to July 2020), PEDro (to July 2020), and CINAHL (1982 to July 2020). No language restrictions were used. Titles and abstract screening, as well as full text reviews were performed by two independent reviewers. Disagreements were arbitrated by a third, independent reviewer. Reference lists of all included studies were screened to ensure no study is missed. The quality of each study was assessed by extracting PEDro scores from the Physiotherapy Evidence Database (www.pedro.org.au). Review Manager software (RevMan 5.4) was used to analyse the data.

The search strategy enabled retrieval of 5043 records. A total of 212 records were included in full-text review and 10 were eligible for inclusion (participant n = 894). The PEDro scores ranged from 5 to 8. Majority had ischemic stroke (71%) and the mean age of participants ranged from 38 to 67 years. Two electrical stimulation methods were reported in the studies: Transcutaneous Electrical Nerve Stimulation (TENS; n=5) and electroacupuncture (n = 5). Percutaneous Tibial Nerve Stimulation (PTNS) was not used in any of the included trials. 
Heterogeneity was high when all data from TENS studies were pooled (I2 = 95%), and was reduced when studies were grouped by frequency of therapy sessions per week (I2 = 69%). Figure 1 shows that TENS has a large effect when performed daily (SMD = -3.40, 95% CI -4.46 to -2.34), and a medium effect when TENS was performed less than daily (SMD = -0.67, 95% CI -1.09 to -0.26).
Heterogeneity was also high when data from all electroacupuncture studies were pooled (I2 = 94%), and reduced when studies were grouped by the number of therapy sessions per week (I2 = 62%). Figure 2 shows electroacupuncture has a large effect when administered daily or more than 5 times a week (SMD = -2.32, 95% CI -2.96 to -1.68), and a small effect when administered 5 times a week (SMD = -0.44, 95% CI -0.69 to -0.18.

Both daily TENS and electroacupuncture more than 5 times per week have large beneficial effects on post-stroke urinary incontinence. These results resonate with the findings that increased time-course of peripheral electrical stimulation is associated with cortical plasticity[2] and that daily TENS for more than three weeks generated persistent neuroplastic changes in the cerebral cortex of healthy volunteers[3]. Imaging studies that demonstrate changes in brain regions known to have a role in continence functions may help in understanding the mechanism of action of these therapies.

Daily treatment with electrical stimulation with non-implanted devices to treat post-stroke urinary incontinence shows a promising treatment effect. Further investigation in randomised controlled trials is required before recommending use in routine clinical post stroke care.

L. Shamseer et al., “Preferred Reporting Items for Systematic Review and Meta-analysis Protocols (PRISMA-P) 2015: Elaboration and Explanation,” BMJ  Br. Med. J., vol. 349, no. January, pp. 1–25, 2015, doi: 10.1136/bmj.g7647.
L. S. Chipchase, S. M. Schabrun, and P. W. Hodges, “Peripheral Electrical Stimulation to Induce Cortical Plasticity: A Systematic Review of Stimulus Parameters,” Clin. Neurophysiol., vol. 122, no. 3, pp. 456–463, 2011, doi: 10.1016/j.clinph.2010.07.025.
R. Meesen, K. Cuypers, J. C. Rothwell, S. P. Swinnen, and O. Levin, “The Effect of Long-term TENS on Persistent Neuroplastic Changes in the Human Cerebral Cortex,” Hum. Brain Mapp., vol. 32, no. 6, pp. 872–882, 2011, doi: 10.1002/hbm.21075.