Clinical Application of Sacral Neuromodulation

Indications

Neuromodulation of the sacral nerves is a therapeutic option for voiding dysfunction in patients who do not respond to the common non-invasive therapies and in whom disturbance in reflex coordination between the bladder, sphincter and pelvic floor is suspected. The rationale for using electrical stimulation techniques for the treatment of such voiding dysfunction is that this stimulation turns the neurological control mechanism back towards a more functional status. The main indications are urge incontinence, OAB syndrome, urinary retention and chronic pelvic pain.

OAB syndrome, which is also called urge syndrome or urgency-frequency syndrome, is characterized by urgency, with or without urge incontinence, usually with increased daytime frequency and nocturia, in the absence of local or metabolic factors explaining these symptoms [4]. In patients suffering from an OAB, sacral neuromodulation is an appealing therapeutic modality for symptoms refractory to conventional pharmacotherapy, and is relevant for both neurologic and non-neurologic causes.

In patients suffering from chronic urinary retention, sacral neuromodulation should be reserved for functional urinary retention without evidence of mechanical obstruction. Various indications such as Fowler's syndrome, spastic pelvic floor syndrome and bladder hypo/acontractility have been proposed.

Pelvic pain syndrome is the occurrence of persistent or recurrent episodic pelvic pain associated with symptoms suggestive of lower urinary tract, sexual, bowel or gynecological dysfunction, without any infection or other obvious pathology [4]. Chronic pelvic pain is defined as pain of a minimum of 6 months duration that is not related to any identifiable cause or etiology [125]. In patients suffering from chronic pelvic pain, sacral neuromodulation could be indicated when the symptoms are refractory to conventional pharmacotherapy after exclusion of obvious local pathological conditions.

Evaluation

Before the implantation of a neuromodulatory device, each patient should undergo a minimal investigation performed to confirm the pertinence of the indication, exclude any contraindications and to have baseline values.

The work-up for treatment by sacral neuromodulation must include careful assessment of past history with special emphasis on drugs influencing bladder function. A physical examination may be given to assess neurologic status, togther with a perineal examination with urodynamic investigation to assess bladder and sphincter function. To rule out any other lower urinary tract pathological conditions, urine culture can be performed to exclude urinary tract infection. Cytology and cystoscopy are helpful in ruling out carcinoma cystitis, and when indicated, imaging of the upper tract may be performed. It is recommended to perform MRI of the entire spinal cord to screen for neurologic diseases such as multiple sclerosis, a neoplasm, syringomyela, lipoma, etc.

For treatment of incontinence, the primary outcome measure should include a voiding diary recording the number of episodes of incontinence and micturition during a specified time. Recording the mean number of pads used per 24 hours may be helpful. For some authors, the quantification of the amount of urine lost during the pad test is also recommended [14]. Patient assessment of the severity of the symptoms can be recorded by a validated urinary incontinence outcome score, such as the Urogital Distress Inventory, the Bristol Female Lower Urinary Tract Symptoms or the Incontinence Impact Questionnaire [89, 90, 141, 168]. Many scores, such as the Short-form-36 (SF-36) and Beck Depression Inventory (BDI), may be used to evaluate the repercussion of the incontinence on quality of life [163]. Even if there is no systematic correlation between severity of clinical OAB symptoms and urodynamic parameters of detrusor over-activity, most authors recommended the use of cystometrograms to evaluate the responsiveness to sacral neuromodulation. The maximum cysto-metric capacity (volume at which the patient feels he/she can no longer delay micturition), the reflex volume (volume at which the first uninhibited contraction of the detrusor occurs), the sensation of bladder filling and the degree of bladder compliance (relationship between change in bladder volume and change in detrusor pressure) may reflect the extent of bladder activity.

In the treatment of urinary retention, the primary outcome measure should be the post-void residual urine [14]. Most authors recommended evaluating the mean voided volume and the mean number of intermittent catheterizations per 24 hours. Urodynamically, it seems reasonable to evaluate the urine flow with pressure flow studies (measuring the relationship between pressure in the bladder and urine during bladder emptying) or, at least by recording flow rate and voiding time, to assess bladder contractility during cystometry.

For painful bladder syndromes, the primary outcome measure should ideally be based on a validated pain assessment instrument. In addition, patients considered candidates for implantation may have benefited from psychological screening [14].

Pediatric Setting

There are some specific etiologies of urinary dysfunction in children, such as neurogenic bladder (myelomeningocele, occult spinal dysraphism, sacral agenesis, tethered cord syndrome, cord lipoma, cerebral palsy), non-neurogenic bladder (anatomic bladder exstrophy), functional bladder (en-uresis, urinary infection), and non-neurogenic neurogenic bladder (Hin-man syndrome). Various electric stimulation modalities are possible in children.

Intravesical electrical stimulation (IVES) is used to treat underactive detrusor, idiopathic or neurogenic in children. IVES is given by a catheter electrode in the bladder (cathode) with the anode attached to the supra-pubic abdominal skin or the thoracic region. Continuous stimulation from 20 to 100 Hz is delivered (pulses = 0.2 to 10 ms, intensity from 0.1 to 64 mA). Sessions are 60 to 90 min daily over a period of 3 weeks to 3 months. For Gladh et al. [65], the frequency of urinary tract infections and incontinence decreased significantly and long-term normalization of voiding was obtained for 83% children with idiopathic problems and 40% with neurogenic problems. Another study [18] showed an absence of improvement in patients with myelomeningocele. This kind of stimulation is proposed as an alternative to clean intermittent catheterization.

Transcutaneous stimulation may be attempted to treat urinary urgency and incontinence in children. Current is delivered via skin electrodes for a short duration daily on a home treatment basis. Surface electrodes are placed at the level of the sacral root S3. Stimulation of 2 Hz is applied from 1 to 2 hours every day. For non-neurological bladder dysfunction, dryness improved in 73.3% of children, with a significant increase in mean voided volume [82]. 68% responded after 1 month of trial therapy with an increase in bladder capacity, decrease in urgency, and decrease in incontinence and/or better sensitivity. In the series of Hoebeke et al., 56% of children were cured after 1 year. In a randomized controlled trial, no difference was found between the active spina bifida group and the placebo group [112].

Sacral neuromodulation was applied in children at the beginning of the nineties [153]. Contrary to adults, there has been no large randomized prospective study. Recently, a prospective randomized study [75] reported results of sacral neuromodulation in 42 patients (spina bifida in 38 cases) from 5 to 19 years old (mean age 11.9 years). Patients were compared (clinical examination, voiding diary, urodynamic evaluation) every three months for a minimal period of 12 months. Despite the improvement noted in implanted patients, the difference was not significant between the two groups. A multicenter study now seems to be necessary to increase the number of patients. The integrity of the nerves (even incomplete) is also a predictive factor of success.

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