Electrical neuromodulation of the lower urinary tract began over a century ago, but it was the pioneering work of Tanagho and Schmidt in the late 1980s that demonstrated electrical activation of efferent fibres to the striated urethral sphincter inhibited detrusor contractions [1]. Stimulation of the third sacral root (S3) has been shown to be effective in stimulating the urethral sphincter [2].It became evident that sacral neuromodulation (SNM) may thus restore voiding in women with chronic urinary retention [3].  

Although SNM is efficacious, it is not without its complications and need for revision surgery. Therefore, it is important that patients are counselled regarding failure of the procedure (often quoted as being 25%), the risk of IPG site pain, sciatica, nerve injury. We now have long-term outcome data on our centre’s experience of SNM for urinary retention over the last 28 years (1996-2024).From 2004 to date, we exclusively used the tined lead and the 2-stage approach. Prior to that we used percutaneous nerve evaluation and insertion of a complete SNM system. For the purposes of this study, we wish to present the outcomes from patients implanted prior to December 2004, so we can determine long term efficacy of SNM and any complications that arose.


AIM AND OBJECTIVES
Patients implanted with an SNM device between 1996-2004 were studied, with a view to evaluate:
1.	The long- term efficacy of SNM 
2.	The revision rate of SNM implants
3.	The incidence of complications encountered

A retrospective analysis of patients who underwent SNM insertion from 1996 – 2004 was carried out at a single tertiary centre at the National Hospital for Neurology and Neurosurgery. Twenty-two patients were identified. All underwent a 2-stage SNM for chronic urinary retention at our tertiary referral centre. Following insertion of a percutaneous nerve electrode or a Tined lead (Stage 1 SNM) all patients were evaluated for a period of 2-4 weeks to determine efficacy. This was defined as normalisation of urinary function, typified with restoration of voiding and complete bladder emptying. Those in whom Stage 1 was successful, went on to have an implantable pulse generator (IPG) inserted (Stage 2 SNM). 

Details of surgical and long-term complications, electrode revisions, and IPG replacements were noted over the intervening 27 years.

Data was collated from our database and hospital notes.

21 patients were female, and one was male. All women were diagnosed with primary disorder of urethral sphincter relaxation on urethral pressure studies and urethral sphincter EMG, commonly known as Fowler’s syndrome at the time. The male patient had voiding dysfunction and chronic urinary retention. 

The average age of SNM insertion was 35.5 years (range: 24 – 49 years). 

Stage 1 SNM was successful in all but two patients. These 20 successful patients went on to have a Stage 2 procedure with implantation of the IPG, which gave an initial overall success rate of 95%. The patients in whom SNM was not successful were female, and no identifiable cause was determined as to why the SNM did not help their symptoms.

The 20 successful patients were reviewed annually between the date of their Stage 2 implant and 2024. Eleven patients needed to have a  revision of their electrode, and/or IPG site, sometimes on several occasions (Table 1). The reasons for this were either there was history of leg pain ( 30% in this cohort), IPG site pain (20% in this cohort), or electrodes became infected or displaced, usually after some form of trauma. These revisions took place either within a few months of initial implantation or many years later. 

The IPG was replaced roughly every 5-10 years, depending on the electrical parameter settings, with a lower voltage resulting in an extension of the IPG life. 

Over the last two decades seven patients failed to respond to SNM in the long term with inefficacy becoming an issue between 1-10 years after implantation. Those in whom delayed SNM inefficacy became evident were followed up until they were discharged from the service. The cause of the inefficacy could not be determined. Of the 22 patients, 4 patients were deceased from unrelated causes (cancer, ischaemic heart disease and respiratory failure) after having the device for a minimum of 5 years. Their data was included for completeness of the study 

Taking into consideration all the factors determined in this small cohort of patients, the overall long term success rate of SNM in chronic urinary retention was 60%.

This is the first study to look at the long-term follow up in an initial group of patients implanted at least 20 years ago. What is evident is that electrodes do need to be replaced, as do batteries, but despite the factor of time, trauma and limited SNM technology prior to 2004 the success rate in this group of patients is still 60%. 

Over the last decade there has been a huge evolution in neuromodulation technology, involving new approaches and options being made available to patients. Patient selection, better algorithms of management and individualised care has improved not only in the access to this technology but also the outcomes, as demonstrated widely in the literature.

This study harks back to the beginning of the neuromodulation journey in the United Kingdom and demonstrates that from the outset neuromodulation was the foundation of an effective treatment pathway for patients with intractable pelvic floor dysfunction.

Tanagho, E.A. and R.A. Schmidt, Electrical stimulation in the clinical management of the neurogenic bladder. J Urol, 1988. 140(6): p. 1331-9.
Tanagho, E.A., R.A. Schmidt, and B.R. Orvis, Neural stimulation for control of voiding dysfunction: a preliminary report in 22 patients with serious neuropathic voiding disorders. J Urol, 1989. 142(2 Pt 1): p. 340-5.
Swinn, M.J., et al., Sacral neuromodulation for women with Fowler's syndrome. European Urology, 2000. 38: p. 439-443.