Sacral neuromodulation (SNM) involves modulation of spinal cord reflexes and brain networks by low intensity stimulation of the sacral nerve roots (S2,3,4) that in turn influence bladder, bowel and pelvic floor function.(1) Medtronic (Minneapolis, USA) was the first to introduce the Interstim devise for the purpose of SNM which was approved by US FDA in 1997.
Indications with FDA approval: Refractory overactive bladder (OAB); Non-obstructive urinary retention (NOR); Refractory fecal incontinence.
Expanding indications: Fowlers syndrome; Neurogenic lower urinary tract dysfunction in patients with spinal cord injury, Multiple sclerosis, Parkinson’s disease and Spina bifida; Interstitial cystitis or painful bladder syndrome (IC/PBS); Nonneurogenic voiding dysfunction; Refractory constipation; Sexual dysfunction.(2)
SNM is never the first line treatment for the above-mentioned indications. It is only considered after failure of conservative and medical treatment. In India, high cost is the most important prohibitive factor for SNM and the cost of the neurostimulator Interstim IITM is approximately 8 lakh rupees.
Surgical procedure: SNM involves a two-stage procedure done under either local or general anesthesia. First stage is the trial period of 5-7 days in which neurostimulation of the quadripolar tined lead (Figure 1) placed over the S2,3,4 nerve roots is done by an external nerve stimulator. Clinical response rate of >50% improvement in symptoms suggests a successful trial. Then the second stage procedure is done after 1-2 weeks during which the nerve stimulator (Interstim II devise) is implanted subcutaneously in the ipsilateral upper and outer quadrant gluteal region through a 3-4 cm incision (Figure 2).
Outcome: Siegel et al have shown 50% reduction in urinary leak episodes per day at 3 years follow up in 56% of patients with urgency urinary incontinence.(3) They also evaluated the quality of life and safety of Interstim placement at 5 years follow up and showed a success rate of 82%. In patients with NOR, it was seen that 70% patients no longer needed self-catheterization after 6 months of implant placement. Studies have also shown 60-75% reduction in mean number of catheterizations per day and also reduction in post void residuals.(4)
Authored by Dr Sudheer K Devana PGI, Chandigarh
Figure 1: A) Intraop fluoroscopy image showing correct placement of quadripolar tined lead through the S3 sacral foramen with outward lateral curvature configuration. B) The subcutaneous pocket with the Interstim II neurostimulator devise placed in the upper outer quadrant of right gluteal region.