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Keywords:

  • detrusor overactivity;
  • detrusor wall thickness;
  • overactive bladder;
  • ROC analysis;
  • translabial ultrasound

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Objective

The measurement of detrusor wall thickness has been used as a screening test for detrusor overactivity and bladder outlet obstruction in men and women. The aim of this study was to determine, using receiver–operating characteristics (ROC) analysis, the diagnostic value of detrusor wall thickness in predicting detrusor overactivity in women.

Methods

The records of 686 women who attended a tertiary urodynamics service from November 2002 to January 2006 were retrospectively reviewed. The patients had undergone an interview, clinical examination, multichannel urodynamic studies and translabial ultrasound examination. Detrusor wall thickness measurements were taken at the bladder dome, after bladder emptying. ROC analysis was used to identify the optimal cut-off of detrusor wall thickness in predicting detrusor overactivity.

Results

Average detrusor wall thickness in the detrusor overactivity group was 4.7 ± 1.9 mm (mean ± SD), compared to 4.1 ± 1.6 mm in the non-detrusor overactivity group (P < 0.001). Using a cut-off of detrusor wall thickness of 5.0 mm gave a sensitivity of 37% and a specificity of 79% for diagnosing detrusor overactivity. The ROC analysis revealed an area under the curve (AUC) of 0.606 (95% CI, 0.56–0.65).

Conclusions

There is a statistically significant association between detrusor wall thickness and detrusor overactivity (P < 0.001). However, ROC analysis demonstrated that detrusor wall thickness as measured by translabial ultrasound is of little use as a diagnostic test for detrusor overactivity, giving an AUC of only 0.606. Measurement of detrusor wall thickness should therefore not be used as a diagnostic parameter for detrusor overactivity in women. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Female lower urinary tract symptoms, including urinary incontinence, urgency, frequency, nocturia and voiding dysfunction, may occur secondary to morphological and functional anatomical changes of the urogenital organs. Detrusor muscle hypertrophy has been described in association with a number of disorders of the lower urinary tract. It has been hypothesized that detrusor hypertrophy may be secondary to isometric contraction against a closed sphincter and/or against an obstructed bladder outlet1, 2. In recent years ultrasound has been used as a diagnostic technique for assessing the morphology and dynamic anatomy of the female lower urinary tract. It has become a routine diagnostic method for female urinary incontinence and female pelvic organ prolapse3, 4, and supplies additional information in patients with voiding dysfunction. In men, sonographic measurement of bladder wall thickness is widely used as a screening test for bladder outlet obstruction and detrusor overactivity5–7. However, the correlation between detrusor wall thickness and detrusor overactivity in women remains unclear. Khullar et al.2 found high sensitivity and specificity when using a cut-off of 5 mm for detrusor wall thickness as a screening test for detrusor overactivity. In 2002, Robinson et al.8 concluded that detrusor wall thickness of more than 6 mm may be used as a diagnostic tool for detrusor instability. However, these findings have not been replicated by other units, and were in fact contradicted by a recent large study9 in an ethnically different population.

The aim of this study was to determine the nature of any association between detrusor wall thickness and detrusor overactivity in our (largely Caucasian) population and to define receiver–operating characteristics (ROC) for detrusor wall thickness as a test for detrusor overactivity and urge incontinence in women.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

We retrospectively reviewed the records of 792 consecutive female patients who visited our tertiary urogynecological service from November 2002 to January 2006, and identified those who had undergone a full multichannel urodynamic study and translabial ultrasound. The urodynamic study included free uroflowmetry, and filling and voiding phase cystometry using a fluid-filled system (Uromac Acquidata, Neomedix, Sydney, Australia). Translabial ultrasound was carried out using either an ATL/Philips HDI 1000 (Philips Medical Systems, Seattle, USA), a Medison SA 8000 (Seoul, Korea) or a Toshiba Capasee (Tokyo, Japan) ultrasound machine, equipped with 4–8-MHz curved array two-dimensional transducers, and was performed after bladder emptying and catheter removal, at a maximum bladder volume of 50 mL as estimated by translabial ultrasound and using a formula originally proposed for transvaginal ultrasound estimation of residual urine10. Detrusor wall thickness was defined as the thickness of the iso- to hypoechogenic layer at the bladder dome opposite the internal urethral meatus within 2 cm of the midsagittal plane11. Three separate measurements were made, and the mean calculated (Figure 1).

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Figure 1. Translabial ultrasound images in the midsagittal plane used to measure detrusor wall thickness. The images are from four different patients, with measurements covering a large part of the range of thickness to be expected in non-neuropathic patients. Means are: a, 2.4 mm; b, 3.7 mm; c, 4.4 mm; and d, 6.8 mm.

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A blinded interobserver test–retest series on detrusor wall thickness (bladder dome) measurement was performed in 67 women. This test–retest series was performed within one fortnight by the two authors, after completion of the main study and on a later population with similar clinical characteristics. We used archived cine volume loops obtained using equipment capable of three-dimensional imaging, giving a choice of multiple (> 10) volume datasets for analysis.

SPSS 13.0 for Windows (SPSS Inc., Chicago, IL, USA) was used for statistical analysis, and normality was tested by the Kolmogorov–Smirnov method. The strength of associations between symptoms and urodynamic detrusor overactivity was evaluated using odds ratios. Student's t-test was used to test for statistically significant differences between the mean values of detrusor wall thickness of the different urodynamic diagnoses, and one-way ANOVA was used to test the differences between mean values of detrusor wall thickness at different severity levels of anterior compartment prolapse. ROC curves were used to determine the diagnostic value of detrusor wall thickness in predicting detrusor overactivity, and P < 0.05 was considered statistically significant. Terminology and units conformed to the standards recommended by the International Continence Society (ICS), except when otherwise noted12. In particular, we did not use the disputed ICS definition of ‘overactive bladder syndrome’. The local Human Research Ethics Committee approved retrospective data analysis without individual patient consent (reference WAHS 05–029).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

After exclusion of missing data (owing to high residuals (over 90% of missing data) or to operator error), 686 datasets remained. The mean age of the women was 53.7 ± 13.4 (range, 17.9–89.4) years. There was no correlation between detrusor wall thickness and age (r = 0.001, P = 0.492). Two hundred and twenty-nine women (33.4%) were diagnosed with significant bladder prolapse (Grade 2 + ), and there was a negative association between bladder prolapse and detrusor wall thickness (P = 0.014 on ANOVA). The most common overactive bladder symptom reported in the study population was urge incontinence (n = 503, 73.3%). Two hundred and fifty-one (36.6%) women reported the symptom of frequency, and 320 (46.6%) complained of nocturia. We do not routinely question patients on urgency since this is a difficult symptom to quantify.

On multichannel urodynamic testing, we diagnosed detrusor overactivity in 184 women (26.8%), and sensory urgency in 135 patients (19.7%). Of 503 urge-incontinence cases, 171 (34.0%) had detrusor overactivity detected on urodynamics (odds ratio (OR), 6.7; 95% CI, 3.7–12.2; P < 0.001) whereas 101 (20.1%) had sensory urgency (OR, 1.1; 95% CI, 0.7–1.7; P = 0.66). In 251 patients with symptoms of frequency, 83 (33.1%) had detrusor overactivity (OR, 1.6; 95% CI, 1.2–2.3; P = 0.005) and 61 (24.3%) had sensory urgency (OR, 1.6; 95% CI, 1.1–2.3; P = 0.02). In the group of 320 patients with the symptom of nocturia, the odds ratios were 2.9 and 1.4 for detrusor overactivity and sensory urgency, respectively (Table 1).

Table 1. Strength of the association between symptoms of the overactive bladder and urodynamic findings
SymptomDetrusor overactivitySensory urgency
Odds ratio (95% CI)POdds ratio (95% CI)P
Frequency1.6 (1.2–2.3)0.0051.6 (1.1–2.3)0.02
Nocturia2.9 (2.1–4.2)< 0.0011.4 (1.0–2.1)0.05
Urge incontinence6.7 (3.7–12.2)< 0.0011.1 (0.7–1.7)0.66

Average detrusor wall thickness in the detrusor overactivity group was 4.7 ± 1.9 mm compared to 4.1 ± 1.6 mm in the non-detrusor overactivity group, a statistically significant difference (P < 0.001). There was no statistically significant difference in mean detrusor wall thickness between patients with and without sensory urgency or with and without voiding dysfunction. Patients with urodynamic stress incontinence on average had lower detrusor wall thickness, although the association was weak (Table 2).

Table 2. Detrusor wall thickness grouped by urodynamic diagnosis
 Urodynamic stress incontinenceDetrusor overactivityVoiding dysfunctionSensory urgency
  1. Data are given as mean ± SD (mm). NS, not significant.

Yes4.1 ± 1.74.7 ± 1.94.2 ± 1.84.1 ± 1.7
No4.5 ± 1.84.1 ± 1.64.3 ± 1.74.3 ± 1.7
P0.014< 0.001NSNS

Different cut-off values of detrusor wall thickness for the diagnosis of detrusor overactivity with the corresponding sensitivity, specificity, and positive and negative predictive values are shown in Table 3. At a cut-off of 5 mm, sensitivity and specificity of detrusor wall thickness were 37% and 79%, respectively, while at a cut-off of 6 mm, sensitivity was 22% and specificity was 89%. Figure 2 shows histograms of detrusor wall thickness in patients with and without detrusor overactivity, and the ROC curve of detrusor wall thickness in predicting detrusor overactivity, with an area under the curve (AUC) of only 0.606. When considering detrusor wall thickness as a test for urge incontinence (Figure 3), the AUC was even lower, at 0.545.

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Figure 2. (a) Histograms of detrusor wall thickness in the detrusor overactivity group (equation image) and non-detrusor overactivity group (equation image). (b) Receiver–operating characteristics curve for detrusor wall thickness in predicting detrusor overactivity; area under the curve = 0.606.

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thumbnail image

Figure 3. (a) Histograms of detrusor wall thickness in the urge incontinence group (equation image) and non-urge incontinence group (equation image). (b) Receiver–operating characteristics curve for detrusor wall thickness in predicting urge incontinence; area under the curve = 0.545.

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Table 3. Detrusor wall thickness cut-off values for the diagnosis of detrusor overactivity
ParameterDetrusor wall thickness (mm)
≥ 5.0≥ 6.0≥ 7.0
Sensitivity (%)372213
Specificity (%)798995
Positive predictive value (%)404047
Negative predictive value (%)777677

The blinded interobserver test–retest series on detrusor wall thickness (bladder dome) performed in 67 women yielded an intraclass correlation coefficient (average measures, absolute agreement definition) of 0.82 (95% CI, 0.63–0.91), which signifies excellent reliability.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Detrusor overactivity is a common problem in women, with urodynamic studies being accepted as the sole diagnostic criterion. However, urodynamic testing is invasive, expensive, time consuming and may be technically difficult. Several workers have tried to develop a simpler, non-invasive diagnostic technique by using ultrasound measurement of detrusor wall thickness. The basic theory behind this diagnostic concept is that detrusor wall thickening in patients with detrusor overactivity is presumed to be the result of multiple isometric contractions against a closed (or initially closed) outlet, i.e. a muscle training effect. Therefore, it is plausible to assume a relationship, whether causal or by association, between increased detrusor wall thickness and detrusor overactivity. In confirmation of this concept, this large observational study found a statistically significant correlation between detrusor wall thickness and detrusor overactivity, patients with detrusor overactivity showing higher detrusor wall thickness (4.7 ± 1.9 mm vs. 4.1 ± 1.6 mm, P < 0.001).

ROC analysis, however, demonstrated clearly that detrusor wall thickness is of little use as a diagnostic test for detrusor overactivity, giving an AUC of only 0.606. A good diagnostic method should yield both high specificity and sensitivity, and this was not the case. The sensitivity and specificity when using a previously published cut-off of 5 mm were 37% and 79%, respectively2. When using a cut-off of 6 mm—as suggested by Robinson et al.8—the specificity was increased to 89% but sensitivity decreased to 22%.

This study may be criticized for the fact that we did not use transvaginal ultrasound as originally described by Khullar et al.13, and that we measured only at the dome. However, the advantages of translabial over transvaginal ultrasound are substantial, particularly in regard to reduced invasiveness and lack of distortion, and the disadvantages are very few. With regard to measuring the trigone, we have found that trigonal measurements are even less predictive of detrusor overactivity and/or symptoms of bladder irritability (own unpubl. data) and less reproducible, probably owing to the varying thickness of trigonal muscle, which is why we limited ourselves to measuring at the dome. The discrepancy in the diagnostic value of detrusor wall thickness as measured by either the transvaginal or the translabial route is clearly not due to inferior accuracy or reliability of the translabial method, as we were able to document excellent repeatability of this method. However, we are unable to exclude the possibility that detrusor wall thickness may perform better as a test when following the originally published protocol, and therefore our conclusions have to be limited to the translabial method. Equally, associations between detrusor wall thickness and diagnoses made using ambulatory urodynamics8, a rarely used diagnostic method, may be higher than those observed by us.

We found no association between patients' age and detrusor wall thickness, which again contradicts previous findings by others14, and also no evidence for the assumption that increased detrusor wall thickness is due to multiple detrusor contractions over a long period of time, resulting in isometric muscle training. If there is such a training effect then we would have to assume that in our population its impact was canceled out by unknown confounders. Finally, we observed a negative association between detrusor wall thickness and anterior compartment prolapse, which is consistent with previous findings of a significant negative association between bladder prolapse and symptoms and signs of the overactive bladder15.

In conclusion, measurement of detrusor wall thickness by translabial ultrasound should not be used as a diagnostic parameter for detrusor overactivity in women. While there is an association between increased detrusor wall thickness and detrusor overactivity on urodynamic testing, ultrasonic measurement of detrusor wall thickness clearly cannot replace urodynamic testing.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References