Detrusor underactivity (DU) is the low detrusor pressure or short detrusor contraction time, usually in combination with a low urine flow rate resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying within a normal time span [1]. As much as 48% of older men and 45% of older women undergoing evaluation for lower urinary tract symptoms (LUTS) show evidence of DU [2]. These patients may be affected by symptoms or require catheterisation for bladder drainage. Risk factors for underactivity  are damage of the spinal cord, especially  lumbal and sacral portion,  diabetes mellitus, detrusor decompensation as result of the  bladder outlet obstruction. The diagnosis of DU it is established on the basis of  the results pressure-flow study. Currently, approaches to the treatment of patients with detrusor underactivity are  contradictory and the effectiveness of therapy is insufficient. Most commonly intermittent catheterisation are used. One of the causes  of DU is the impairment of the innervation or even denervation of the detrusor. Extracorporeal magnetic stimulation of the pelvis  (EXMS)  improves innervation and contraction pelvic muscles [3]. EXMS  was firstly proposed for clinical use in 1998 in the United States by N. T. M. Galloway (Neocontrol, Neotonus, Inc,.  USA) for treatment stress urinary incontinence [3]. Above mentioned  authors named this procedures as extracorporeal magnetic innervation to emphases innervation improving. There are  the data presented about  effectiveness of extracorporeal magnetic stimulation in women with stress urinary incontinence, urgency and mixed urinary incontinence, postprostatectomy incontinence, chronic prostatitis/chronic pelvic pain syndrome.  
The aim of the our pilot study  was to determine   the effectiveness of EXMS in the treatment of detrusor underactivity.

In the pilot  study were included 16 patients, 10 men and 6 women. The mean age was 53.3±7.3 years. They have symptoms incomplete bladder emptying, impaired bladder sensation, weak flow and straining.  Four patient had indwelling catheters because cannot void after transurethral prostate resection (TURP). 2 women were underwent hysterectomy.  The diagnosis DU was established  by  urodynamic study and bladder contractility index  (BCI) was used to define detrusor underactivity (BCI less than 100). Patient with neurogenic origin  of DU were not included.
EXMS was performed by  a system extracorporal magnetic stimulation of the pelvis  "Avantron", manufacturer "Rehabilitation technologies", Russia. During the procedures patients seat on chair with magnetic field generator. Stimulation was carried out continuously at a frequency of 23 Hertz for 20 minutes, 2-3 times a week, the course of treatment was 12 procedures, intensity of magnetic field selected individually to avoid unpleasant sensation during procedure.   The effectiveness was evaluated by IPSS questionnaire, voiding diary,  uroflowmetry and residual urine volume measurement.

After extracorporeal magnetic stimulation, subjective improvement was noted in 11 (68.7%) patients with DU, the severity of symptoms significantly decreased and the quality of life improved. The severity of symptoms by IPSS questionnaire decreased  from 20,9±7,4 to 13.9±4.9 (p<0.05). The quality of life has improved  from 4,7±0,2  to 2,5±0,3.
Noteworthy is the significant increase in the maximum flow  on 26%: from 8.7 ± 0.9 ml/s to 11.8 ± 1.8 ml/s (p<0.05) and a significant decrease in the residual urine volume  from 174.6±18.8 ml to 87.8±17.5 ml (p<0.05). At two non-voiders after TURP urination become compensated (maximal flow in uroflowmetry more than 10 ml/s, postvoid residual less than 100 ml) and a indwelling  catheter was successfully removed.

Our results shows some improvement in symptoms and objective parameters in patient with DU. The procedure was well tolerated, there were no any adverse events. The therapeutic effect, in our opinion, was caused by  excitation of peripheral nerve fibers, contractions and training of striated muscles of the pelvic floor, smooth muscle elements of the bladder, urethra, blood vessels and  improvement of microcirculation

Our pilot study showed that EXMS of the neuromuscular portion of the pelvis can be one of the options for the treatment of patients with detrusor underactivity. The further research EXMS in DU is necessary to determine the mode of the stimulation, indications, to define the effectiveness, to obtain and prove the  information on the mechanisms of action.

D’Ancona C, Haylen ?, Oelke M et al. The International Continence Society (ICS) report on the terminology for adult male lower urinary tract and pelvic floor symptoms and dysfunction. Neurourology and Urodynamics. 2019;1–45.
Chapple CR, Osman NI, Birder L et al. The Underactive Bladder: A New Clinical Concept? European Urology 68, 2015, 351-353
N.T.M. Galloway et al. Update on extracorporeal magnetic innervation (ExMI) therapy for stress urinary incontinence. Urology. Supplement. 2000.? 6?. P. 82-85.