AIMS.
Sacral neuromodulation is a treatment option for patients with detrusor
instability [1]. This method has also
been shown to decrease urethral resistance
during voiding [2]. We previously
found that urethral resistance was
higher in a group of females with
detrusor instability than in females
with mixed incontinence or stress
incontinence or females without a
demonstrable cause of the incontinence
and postulated that functional obstruction
could be a potential cause of instability
[3]. In the present study, we examined
the relationship between the decrease
of urethral resistance and that of
the grade of instability in patients
with detrusor instability treated
with neuromodulation. In addition,
we examined if the symptomatic changes
as derived from voiding / incontinence
diaries depended on urethral resistance.
Such a study might contribute to the
understanding of the role of voiding
characteristics in the signs and symptoms
of detrusor instability.
METHODS.
Neuromodulation is applied at our department since 1990. Voiding /
incontinence diaries and cystometric
studies with subsequent pressure /
flow studies before and 6 months after
the operation are part of the evaluation.
Cystometry is done in the supine and
standing position and, after implantation,
with the stimulator on and off. The
pressure / flow studies are done in
the standing position. Only patients
with symptoms of urge incontinence
and urodynamically demonstrated detrusor
instability who had passed the 6 month
evaluation period were included in
the present study. The maximum detrusor
pressure Pmax during the filling phase
was used as the parameter characterising
the grade of instability. Urethral
resistance was characterised by URA.
In addition, the maximum flow rate
Qmax and the associated detrusor pressure
pQmax were determined. The
measurements in the standing position
and, after
implantation, with the neurostimulator on, were used. Three
categories of symptomatic success
were defined:
a more than 90% decrease in the number
of pads used per day or the number
of incontinence episodes per day was
considered a cure, a decrease between
50 and 90% was considered a partial
success and a decrease of less than
50% was considered a failure.
RESULTS.
Of
the 47 patients implanted so far,
44 (38 women, 6 men, mean age 46 years)
underwent the 6 month follow-up examinations.
Symptomatically, 23 patients were
cured, 15 were a partial success and
in 6 treatment failed. The table summarises
the mean values and interquartile
ranges of the urodynamic parameters
for all patients and for the symptomatic
categories separately. On average,
Pmax as well as URA decreased significantly
(paired t-test: p=0.004 and p<0.0005,
respectively). Qmax increased significantly
(p=0.007). The change in pQmax, however,
was not significant (p=0.19). The
high initial mean values of URA and
pQmax in the patients who failed were
caused by one patient only: they were
19 and 39 cm H2O, respectively,
in the remaining 5 patients. None
of the parameters listed in the table
demonstrated significant differences
between the symptomatic categories
(unpaired t-tests, Kruskal-Wallis
test). The figure demonstrates the
relationship between the changes in
Pmax and URA. The Pearson correlation
coefficient r was 0.27, which was
not significant (p=0.081). The Spearman
rank correlation coefficient rho,
however, was 0.34, which was significant
(p=0.024). No dependence of the relationship
on the symptomatic category was found.
The relationship between the changes
in Pmax and those in the voiding pressure
pQmax looked very similar, but significance
was reached in both tests (r = 0.52,
rho = 0.54, p<0.0005).
|
|
|
All
(44)
|
Cure
(23)
|
Partial
(15)
|
Fail
(6)
|
|
Pmax
|
before
|
42
(25 - 56)
|
47
(25 - 59)
|
37
(25 - 50)
|
35
(22 - 56)
|
|
(cm
H2O)
|
after
|
30
(10 - 45)
|
30
(17 - 41)
|
33
(14 - 45)
|
28
(6 - 48)
|
|
|
change
|
-12
(-27 - -1)
|
-18
(-30 - -2)
|
-5
(-20 - 4)
|
-7
(-16 0)
|
|
URA
|
before
|
21
(14 26)
|
18
(14 19)
|
22
(11 28)
|
28
(14 39)
|
|
(cm
H2O)
|
after
|
16
(11 20)
|
15
(12 20)
|
16
(12 22)
|
18
(8 31)
|
|
|
change
|
-5
(-8 1)
|
-3
(-5 1)
|
-5
(-11 2)
|
-10
(-19 - -1)
|
|
pQmax
|
before
|
39
(27 50)
|
38
(27 50)
|
38
(29 52)
|
47
(26 69)
|
|
(cm
H2O)
|
after
|
36
(25 44)
|
36
(21 57)
|
37
(24 45)
|
37
(21 57)
|
|
|
change
|
-3
(-11 6)
|
-2
(-8 6)
|
-1
(-10 10)
|
-10
(-24 4)
|
|
Qmax
|
before
|
13
(8 17)
|
15
(9 17)
|
10
(5 12)
|
12
(7 18)
|
|
(ml/s)
|
after
|
16
(10 20)
|
17
(11 22)
|
14
(10 17)
|
14
(8 20)
|
|
|
change
|
3
(-1 5)
|
2
(-1 4)
|
4
(1 9)
|
2
(-1 6)
|
DISCUSSION.
This study confirms that
neuromodulation reduces the grade
of instability as well as the urethral
resistance during voiding. The correlation
between these two entities, however,
was weak. If the voiding pressure
would be considered a measure of urethral
resistance, the decrease of the instability
could be explained by a decrease
of the resistance for about 25% (coefficient
of determination r2). It
has been shown that symptomatic changes
only poorly correlate with changes
of the grade of instability [1]. It
might be hypothesised that the symptomatic
outcome is correlated more strongly
with voiding phase characteristics
than with filling phase characteristics.
This study does not give evidence
supporting that hypothesis. Apparently
non-urodynamic factors play a significant
role in the success of neuromodulation.
[1].
Curr.Opin.Urol. 8: 287-291, 1998
[3]. Neurourol.Urodynam. 17:
386-388, 1998
[2].
Neurourol.Urodynam. 14: 502-504, 1995
