mechanisms of neuromodulation. However. it does not

explain the beneficial effects of neuromodulatjon in

patients with idiopathic detrusor instability or urgency-

frequency. In conclusion, the mechanism of action of

neuromodulation remains in debate. Stimulation of

afferent pathways seems to play a cruciaI role.

Electrical parameters

Most devices availabIe for eIectrical stimulation use

bipolar (alternating) square-wave pulses [ll]. The

rationale of the bipolarity is the minimization of

electrochemical reactions at the site of the eIectrode

and thereby of the risk of tissue damage. A pulse duration

of 0.2-0.5 ms has been found to be optimaI in inhibiting

the bladder, but Ionger pulses (1 ms) are also usoo.

Physiological!y, the optimal stimulation frequency is 5-

10 Hz or even 5-6 Hz [2]. However, frequencies of

< 10 Hz soon become unpIeasant when the pulse

amplitude increases. The possible intensity of stimuIation

is therefore limited. This may explain why in some

clinical testing the degree of bIadder inhibition was

independent of the stimuIation frequency at 5-20 Hz.

Some authors use a frequency as high as 50 Hz. The

desired pulse amplitude depends on the neuromoduIation

technique; it shouId be as high as possible in anogenital

electrical stimulation, while a vaIue just above the

detection threshold is considered to be sufficient in sacral

nerve neuromodulation. Intermittent pulse trains are

sometimes used to reduce pelvic floor musele fatigue, but

this mode of stimulation may not be optimal in the

treatment of an overactive bladder [ll].

Anogenital electrical stimulation

The first publications on anogenital electrical stimuIation

as a treatment option in the overactive bladder appeared

in the 1970s [2]. Good results have been described by

mainly Scandinavian and Japanese authors in the 1980s,

and the technique can now be considered an established

treatment [12]; however, satisfaction is not unanimous.

This review focuses on comparative studies of the Iast

decade.

TechTÚl/.ue. The method implies the insertion of plugs

equipped with electrodes into the anal canal and (or) the

vagina (Fig. 1); circular penile eIectrodes are available for

men. Two modes of this type of neuromodulation can

be distinguished. 'Long-term' or 'chronic' stimulation

implies a home-treatment programme for severaI months

(e.g. 3-12). StimuIation is applied daily for many hours

(e.g. 6-8) at a low intensity and may also take place

during the night. This way of stimulation is mainly used

for patients with stress incontinence and is not discussed

here. In 'acute' or 'short-term' maximal stimuIation the

patient is treatOO in a limitOO number of sessions (usually

4-20, sometimes many more) taking 15-30 min each.

The intensity is as high as possibIe. i.e. just beIow the

leveI of discomfort. UsualIy, this is about 1.5-2 times

the perception threshoId [13]. Treatment may take place

weekIy or during a series of consecutive days (sometimes

twice daily) and can be undertaken in the outpatient

clinic as well as at home. In addition to patients with an

overactive bladder onIy, it may also be applied in patients

with mixed incontinence [14]. Re-treatment may be

usefuI.

Evidence. Anogenital electrostimuIation reportOOIy has

a beneficial effect in about half of the patients [14.15],

but the published resuIts vary considerably. While

Eriksen et aI. [16] reported a clinical success rate of

85% and 77% immediateIy after therapy and at 1 year of

follow-up. respectively, KuIseng-Hanssen et aI. [17], also

studying women with idiopathic detrusor instability and

urge incontinence. found no significant improvement in

objective outcome measures, and stopped using the

method. A elo ser examination of the available data is

therefore necessary.

A few studies have compared the effect of electro-

stimulation with that of treatment with a sham device.

Such a device has the same appearance as the normal

equipment, but has no stimulus output. Most authors

found that active treatment was symptomaticalIy and

cystometrically superior to sham treatment [18-20], but

AbeI et aI. [21] found no significant differences. possibIy

because these authors treated postmenopausal women.

Smith [22] found that the symptomatic result of

intravaginal electrotherapy was at least as good as that

of the anticholinergic propantheline bromide.

Suitable patients. Subjective success rates of patients

considering themselves cored or improved are as high as

85% [16], but such rates depend heavily on the selection

of patients. As an example. Primus and Kramer [23]

FIg. 1. Plugs with clcctrodcs Cor anal (lcCt) and vaginal (rlght)

stlmulatlon.