Metabolic syndrome resulting from an excessive accumulation of visceral fat is an important factor that also affects lower urinary tract symptoms (LUTS) including overactive bladder (OAB). Moreover, in recent years, the possibility that frailty, particularly a reduction in the psoas major muscle strength, may also cause LUTS has attracted attention.
However, the relationship of the amount of visceral fat and the volume of psoas major muscle to the onset of LUTS as well as its severity has not been shown. Therefore, the objective of the present study was to clarify the relationship of the visceral fat amount and the psoas major muscle volume to LUTS.

This study enrolled women who underwent an abdominal computed tomography (CT) scan for a health checkup or screening during the last 3 months. Those who did not have a diagnosis of LUTS and were not treated for LUTS before the study were included. Women with a malignant tumor and those with a definite diagnosis of neurogenic bladder were excluded.
For the assessment of subjective symptoms, we used the core lower urinary tract symptom score (CLSS) and the overactive bladder symptom score (OABSS). In the examination of objective symptoms, uroflowmetry was performed and post-void residual urine was measured using ultrasound. On the basis of the OABSS, we defined women with a Q3 (urgency) score of ≥2 and a total score of ≥3 as having OAB.
We analyzed the relationship of LUTS to the visceral fat area (VFA) in the umbilical region, visceral fat volume (VFV), total abdominal fat volume (TAV), psoas major muscle area (PMA) at the level of the third lumbar vertebra, and psoas major muscle volume (PMV) from the upper abdomen to the pelvic region, calculated from abdominal CT scans by using a statistical method.
The visceral fat and muscle measurements were calculated using a 3-dimensional image analysis system (SYNAPSE VINCENT®; Fujifilm, Tokyo, Japan). A value of p < 0.05 was considered to be statistically significant.

The study included 182 subjects in the analysis. The mean age was 57.7 ± 15.3 years. Of the subjects, 71 (39.0%) met the OAB criteria.
1. Relationship between subjective symptoms and CT findings
1.1. Relationship between OABSS and CT findings
On the abdominal CT scans, the VFA, VFV, and VFV/TAV values were all significantly higher in the OAB group than in the non-OAB group (p < 0.001 for all values). The PMA and PMV values were significantly lower in the OAB group (PMA, p = 0.030; PMV, p = 0.004).
Of these parameters, the VFV/TAV value correlated the most with the total OABSS (r = 0.394, p < 0.001). When a receiver operating characteristic curve was drawn for the VFV/TAV value and the presence/absence of OAB, the area under the curve was 0.742 (p < 0.01). When the cutoff value was set to 0.381, the sensitivity was 0.563 and the specificity was 0.811.

1.2. Relationship between CLSS and CT findings
The VFA, VFV, and VFV/TAV values all had a significant positive correlation with the Q3 (urgency) score. Of them, the VFV/TAV value correlated the most (r = 0.457, p < 0.001). In addition, a positive correlation was observed between the VFV/TAV value and the Q7 (straining) score (r = 0.272, p < 0.001).
Both PMA and PMV values had a significant negative correlation with the Q3 (urgency) score. The PMV value had a stronger negative correlation (r = -0.208, p = 0.005). In addition, there were significant negative correlations of both PMA and PMV values with the Q5 (stress urinary incontinence) score (PMA: r = -0.148, p = 0.046; PMV: r = -0.163, p = 0.028).

2. Relationship between findings of objective symptoms and CT findings
In particular, the maximum flow rate negatively correlated with the VFV/TAV value and positively correlated with the PMV value (VFV/TAV: r = -0.289, p < 0.001; PMV: r = 0.304, p < 0.001).

3. Multivariate analysis
A multivariate analysis of VFV/TAV and PMV values and factors that cause OAB and weak urine flow, such as age, sex, and hypertension, showed that a high VFV/TAV value and age were independent risk factors for OAB, like in the univariate analysis (odds ratio: 2.34, 95% confidence interval: 1.05–5.20, p = 0.038). In addition, a low PMV value was shown to be a risk factor for weak urine flow in the multivariate analysis (odds ratio: 2.09, 95% confidence interval: 1.06–4.12, p = 0.033).

On the basis of the above results, excessive accumulation of visceral fat and reduction in the psoas major muscle volume were considered to be factors associated with OAB symptoms and weak urine flow. In particular, excessive accumulation of visceral fat was considered to be a factor that affects OAB symptoms, and reduction in the psoas major muscle volume was considered to be a factor that affects urine flow.

The major limitation of this study is its cross-sectional nature. How altering the body composition by introducing exercise and diet therapy can affect LUTS needs to be prospectively examined.