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ORIGINAL ARTICLE
Year : 2019  |  Volume : 22  |  Issue : 11  |  Page : 1600-1605

Obesity in benign prostatic enlargement: A cross-sectional study comparing sonographic and anthropometric indices of adiposity in a tertiary hospital in Southwestern Nigeria


1 Department of Radiology, Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria
2 Department of Urology, Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Osun State, Nigeria

Date of Submission23-Mar-2019
Date of Acceptance27-Jun-2019
Date of Web Publication13-Nov-2019

Correspondence Address:
Dr. A D Omisore
Department of Radiology, Obafemi Awolowo University Teaching Hospitals Complex, Ilesha Road, PMB 5538, Ile-Ife, Osun State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_165_19

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   Abstract 


Background: Findings from studies on obesity and benign prostatic enlargement (BPE) have been inconsistent. With a previous study done in our facility showing no correlation between anthropometric indices of obesity and BPE, this study aimed at reevaluating the association between obesity and BPE using sonographic indices of abdominal/central obesity. Materials and Methods: Ninety consenting subjects with clinically confirmed BPE had their height and weight [(to calculate body mass index (BMI)] as well as waist and hip circumference [to calculate waist–hip ratio (WHR)] done. The subcutaneous, preperitoneal, and visceral fat thicknesses (SFT, PFT, and VFT, respectively) of these subjects and their prostate volumes were measured on transabdominal Ultrasonography (USS). Transrectal USS was also done to measure the total prostate and transitional zone volumes. Data were analyzed using SPSS version 22. Results: WHR and waist circumference correlated positively with SFT (r = 0.325, P = 0.002 and r = 0.370, P = 0.000, respectively) and PFT (r = 0.209, P = 0.048 and r = 0.313, P = 0.003, respectively). While BMI correlated positively (r = 0.23, P = 0.029) with transrectal transitional zone volume, all three sonographic indices of adiposity correlated negatively (SFT: r = −0.223, P = 0.035; PFT: r = −0.321, P = 0.002; VFT: r = −0.242, P = 0.021) with transrectal total prostate volume. In addition, PFT correlated negatively with transabdominal prostate volume (r = −0.222, P = 0.037) and transrectal transitional zone volume (r = −0.211, P = 0.046). Conclusion: The relationship of BMI with transrectal transitional zone volume was a direct one, while that of SFT, PFT, and VFT with transrectal total prostate volume as well as PFT with transabdominal prostate volume and transrectal transitional zone volume was an inverse one.

Keywords: Benign prostatic enlargement, obesity, preperitoneal fat thickness, prostate volume, subcutaneous fat thickness, visceral fat thickness


How to cite this article:
Asaleye C M, Omisore A D, Onigbinde S O, David R A. Obesity in benign prostatic enlargement: A cross-sectional study comparing sonographic and anthropometric indices of adiposity in a tertiary hospital in Southwestern Nigeria. Niger J Clin Pract 2019;22:1600-5

How to cite this URL:
Asaleye C M, Omisore A D, Onigbinde S O, David R A. Obesity in benign prostatic enlargement: A cross-sectional study comparing sonographic and anthropometric indices of adiposity in a tertiary hospital in Southwestern Nigeria. Niger J Clin Pract [serial online] 2019 [cited 2022 Jan 25];22:1600-5. Available from: https://www.njcponline.com/text.asp?2019/22/11/1600/270853




   Introduction Top


Obesity is the excess accumulation of fat/adipose tissue in the body.[1] Obesity, an established risk factor for cardiovascular diseases (such as hypertension and diabetes mellitus) and certain cancers (such as breast and esophageal), has been shown to promote benign prostatic enlargement (BPE).[2]

Currently, over 500 million adults are obese worldwide and there is a rapid increase in obesity particularly in the developing countries like Nigeria.[3] The prevalence of obesity in Nigeria is currently between 8.1% and 22.2%.[4]

BPE is commoner in Blacks.[5] It has been reported that in Nigeria, the most populous Black nation, one in four men older than 40 years have symptoms suggestive of BPE.[2]

Obesity is commonly assessed using anthropometric parameters such as body mass index (BMI), hip circumference (HC), waist circumference (WC), and waist–hip ratio (WHR).[6],[7] While BMI measures generalized obesity, WC, HC, and WHR measure abdominal (central) obesity.[6] These parameters are fast, easy, and noninvasive.[6] However, they are prone to substantial variations in proportions of visceral fat in people with similar WC, WHR, and BMI. This limitation has been overcome by the use of imaging which has the advantage of direct visualization of the fat layer.[6],[7],[8],[9],[10]

Cross-sectional imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) at the abdominal level is recognized as the standard method for measuring abdominal fat layers which include subcutaneous fat thickness (SFT) (fat layer between the skin and linea alba), preperitoneal fat thickness (PFT) (fat layer between the linea alba and anterior surface of the liver), and visceral fat thickness (VFT) (fat layer between the rectus muscle and posterior abdominal wall).[3],[6] However, the high cost of these modalities and low availability prevent their wide use in clinical and epidemiologic studies.[7],[8],[9] Also, CT has the drawback of exposing patients to ionizing radiation.[8] Ultrasonography (USS) is a simple and noninvasive alternative method of assessing abdominal fat accumulation.[10] The accuracy of ultrasound in estimation of adipose tissue has been shown to be comparable to that of CT and MRI.[10] Cross-sectional imaging, irrespective of the modality (MRI, CT, or USS) used, has the advantage of direct visualization of the fat layer which gives better estimation of abdominal obesity compared with anthropometry.

A previous study in our hospital did not demonstrate any relationship between BMI and BPE using prostate volume measured by transabdominal ultrasound.[11] In this study, we hypothesized that abdominal obesity may correlate better with BPE than generalized obesity. The study therefore aimed to reevaluate the association between BPE and obesity by comparing the correlation between BPE and sonographic indices of adiposity to the correlation between BPE and anthropometric indices of adiposity.


   Materials and Methods Top


Ethical approval for this study was obtained from the Institutional Review Board of our hospital as stated in the Materials and Method section. This prospective, cross-sectional study, approved by the Institutional Review Board of our hospital, was carried out in consenting 90 men above 40 years of age who presented at the urology outpatient clinic with lower urinary tract symptoms (LUTS) over a period of 6 months. Men with documented urinary tract infection, prostatitis, or suspected prostate cancer (nodular prostate from rectal examination or elevated prostate-specific antigen values >4 ng/mL) were excluded. Anthropometric indices of obesity were measured for each subject.[1] The anthropometric indices measured were BMI and WHR. In the erect position and the acanthomeatal line set parallel to the floor, subjects had their weight (kg) and height (m) measured without shoes. Their body weight was measured to the nearest 0.1 kg using a weighing scale (mechanical physician weighing scale attached with a height gauge; model ZT-160, China), while their height was measured to the nearest 0.1 m using a stadiometer. Their BMI was calculated by dividing their weight in kilograms by the square of their height in meters.[12] Using a tape measure, the WC was measured at the level of the noticeable narrowest point, and the HC was measured at the level of the pubic symphysis and maximal gluteal protuberance.[13] WHR was calculated for all study participants by dividing WC by HC.

The sonographic measurements were carried out with a Mindray real-time ultrasound scanner (model DC-7 with Doppler facilities). A transrectal biplanar ultrasound probe (frequency range of 5.0–10.0 MHz) was used for transrectal ultrasound scan of the prostate, while a curvilinear ultrasound probe (frequency range of 3.5–5.0 MHz) was used for the transabdominal ultrasound scan of the prostate and estimation of visceral fat layer. A linear high-resolution ultrasound probe (frequency range of 7.5–12MHz) was used for estimation of subcutaneous and preperitoneal fat layers.

The sonographic indices of obesity measured are subcutaneous fat layer (SFT), preperitoneal fat layer (PFT), and visceral fat layer (VFT) with patients lying supine.[5] VFT was measured as the distance between the anterior wall of the aorta and the internal layer of the rectoabdominal muscle perpendicular to the aorta [Figure 1]. The PFT was obtained by determining the distance between the liver surface and the linea alba [Figure 2], while the SFT was the thickness of the fat tissue between the skin–fat interface and the linea alba [Figure 2].[5] All measurements were made on frozen images that were obtained immediately after expiration to eliminate the influence of the respiratory status.
Figure 1: B-mode sonogram of the abdomen 5cm above the umbilicus showing the level at which VFT was measured. VFT: Visceral fat thickness

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Figure 2: B-mode sonogram of the abdomen at the xiphisternum showing the level at which SFT and PFT were measured. SFT: Subcutaneous fat thickness. PFT: Pre-peritoneal fat thickness

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The total peripheral volume of the prostate gland was measured using transabdominal and transrectal ultrasound techniques. All transabdominal measurements of the prostate were performed with full bladder. Measurements were performed while the patients lay in the supine position. The prostate gland seen inferior to the urinary bladder was scanned in its sagittal and cross-sectional planes. The length was measured on the midsagittal plane as the longest craniocaudal dimension. The height and width were measured as the greatest anteroposterior dimension and longest right to left dimension, respectively, in the cross-sectional plane.[14] The volume of the prostate on transabdominal USS was calculated using ellipsoid formula (π/6 × length × height × width).[15]

The transrectal ultrasound evaluation was carried out with the patients lying in the left lateral decubitus position. The transitional zone is separated from the central and peripheral zones by a hypoechoic band of fibrous tissue (capsule).[16] The midsagittal section image of the prostate was used to measure the length of the whole prostate and transitional zone. The largest cross-sectional (transverse) image was used to measure the width and height of the whole prostate and transitional zone [Figure 3]. All measurements of the transitional zone were done starting from the inner part of the capsule. The length, height, and width of the transitional zone were measured in the planes in which total prostate dimensions were also measured. The width was the longest right to left dimension [measurements 1 and 3 for total prostate and transition zone volumes, respectively, in [Figure 3] and height was the greatest anteroposterior distance [measurements 2 and 4 for total prostate and transition zone volumes, respectively, in [Figure 3] on a cross-sectional scan. The length was the longest craniocaudal distance on midsagittal scan. Transrectal total prostatic and transitional zone volumes were calculated using the formula for volume estimation of an ellipsoid (π/6 × length × height × width).[15]
Figure 3: B-mode transrectal sonogram of the prostate in cross sectional plane showing measurements of the width and height of the total prostate (measurements 1 and 2 respectively) and transitional zone (measurements 3 and 4 respectively)

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The sonographic measurements were performed by the same radiologist, three times and mean values derived to reduce intraobserver variability.

Data from the recruited 90 subjects were analyzed using Statistical Package for Scientific Solutions (SPSS) software (version 22; IBM, Chicago, IL, USA). Descriptive statistics was done for age, anthropometric, and sonographic indices of obesity. Spearman's correlation coefficients for nonparametric data were computed.


   Results Top


The summary of the age and anthropometric values of the study participants is presented in [Table 1]. Their means of the sonographic values are shown in [Figure 4] and [Figure 5].
Table 1: Characteristics of the study population

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Figure 4: Box plots showing mean of subcutaneous fat thickness, pre-peritoneal fat thickness and visceral fat thickness. SFT: Subcutaneous fat thickness. PFT: Pre-peritoneal fat thickness.VFT: Visceral fat thickness

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Figure 5: Box plots showing the mean of transrectal transitional zone volume, transrectal total prostate volume and transabdominal prostate volume

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WHR and WC showed significant positive correlations with SFT (r = 0.325, P = 0.002 and r = 0.370, P = 0.000, respectively) and PFT (r = 0.209, P = 0.048 and r = 0.313, P = 0.003, respectively) [Table 2]. BMI had a positive but weak correlation with transrectal transitional zone volume (r = −0.230, P = 0.029) [Table 3].
Table 2: Spearman' s correlation coefficient for association of the anthropometric indices of obesity with sonographic indices of obesity

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Table 3: Spearman' s correlation coefficient for association of anthropometric indices of obesity with prostate volume

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PFT correlated negatively with transabdominal prostate volume (r = −0.222, P = 0.037), transrectal transitional zone volume (r = −0.211, P = 0.046) and transrectal total prostate volume (r = −0.321, P = 0.002) [Table 4].
Table 4: Spearman' s correlation coefficient for association of sonographic indices of obesity with prostate volume

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SFT (r = −0.223, P = 0.035) and VFT (r = −0.242, P = 0.021) correlated negatively with transrectal total prostate volume only [Table 4].


   Discussion Top


Over the past few decades, different groups of researchers have investigated the influence of obesity and obesity-related disorders on the development of BPE and LUTS, all with conflicting results. Most of these groups concluded that overall obesity or central obesity increases the risk of BPE and LUTS, at least to some degree.[15] In our study, central obesity assessed by BMI did not show correlation with transabdominal prostate volume (r = 0.156, P = 0.144) similar to the findings of the study by Badmus et al.[11] done 7 years earlier in the same tertiary health facility. There is similarity in findings between our study and that of Badmus et al.[11] despite the difference in age range of the participants in the two studies (40–69 years in our study vs 43–88 years in Badmus et al.'s [11] study), although the mean age of the study participants was similar (64.0 ± 9.0 years in our study vs 64.4 ± 8.88 years in Badmus et al.'s [11] study). Even in a multiethnic study [17] including African, European, Asian and South American subjects, the association between obesity and prostate volume was greatest among the men of African descent. Jung et al.,[18] on the other hand, found positive correlation between prostate volume and obesity among Korean men similar to other non-African studies done among Chinese [19] and Asian [20] subjects. It can therefore be deduced that the relationship between obesity and total prostate volume is influenced by ethnoracial factors.

Also on transrectal USS in this study, BMI did not show correlation with the transrectal total prostate volume (r = 0.153, P = 0.149). The enlargement of the transitional zone has been identified as one of the pathologic processes involved in the development of BPE.[21],[22] We therefore went further to evaluate the relationship between transrectal transitional zone volume and BMI and found a positive correlation between them (r = 0.230, P = 0.029) despite noncorrelation between BMI and transrectal total prostate volume. A pathophysiologic explanation for the relationship between obesity and BPE is the effect of obesity on hormones. This includes an increase in estrogen and decrease in testosterone levels, due to aromatization of androgens to estrogens in the adipose tissue.[23] Androgens are involved in the development and maintenance of BPE, as supported by androgen receptor expression in prostate epithelium, and by the observation of high testosterone levels in men with prostate cancer in several although not all studies.[23] It may therefore mean that the transitional zone is the part of the prostate organ that is either sensitive or most sensitive to the effect of generalized obesity. It may also be deduced that the receptors for the high estrogen level seen with obesity are actually expressed in the transitional zone of the prostate gland. A larger population-based study is needed to further evaluate this and validate the findings of this study.

Some studies reported that a reduction occurs in the hyperplastic prostate mass, primarily of the epithelium, and with androgen deprivation. The role of androgens in risk of BPE is also supported by the absence of BPE in men castrated before puberty and by absent or small prostate in men deficient in 5a-reductase type 2. In addition, pharmacological inhibition of dihydrotestosterone, a testosterone metabolite present in the prostate, is associated with a reduction in prostate size, urinary symptoms, and surgery for BPE.[23],[24]

Anthropometric measures of central obesity (WHR and WC) correlated with SFT and PFT but not VFT in this study. WHR and WC in this study did not correlate with transabdominal prostate volume (r = −0.091, P = 0.399), transrectal total prostate volume (r = 0.09, P = 0.390), and transrectal transitional zone volume (r = 0.190, P = 0.072). Kim et al., however, found that prostate volume was positively correlated with central obesity (WC) but not with overall obesity (BMI) in their study.[25]

Contrarily, sonographic measures of central obesity (VFT, PFT, and SFT) showed correlation with prostate volumes in this study. While PFT correlated inversely with all the three categories of prostate volumes (transabdominal prostate volume: r = −0.222, P = 0.037, transrectal transitional zone volume: r = 0.211, P = 0.046, and transrectal total prostate volume: r = −0.321, P = 0.002), SFT and VFT inversely correlated with transrectal total prostate volume only (SFT: r = −0.223, P = 0.035; VFT: r = −0.242, P = 0.021). Zucchetto et al.[24] had previously shown that the later the onset of obesity after 50 years, the more the likelihood of an inverse relationship between obesity and the risk of BPE. The finding of Zucchetto et al.[24] with our finding of inverse relationship between prostate volumes and sonographic indices of obesity would suggest that an inverse relationship is plausible between abdominal/central obesity and BPE.

The positive association between BMI and transrectal transitional zone volume supports the possibility that generalized obesity plays a role in the pathogenesis of BPE. However, the relationship between ultrasound indices (SFT, PFT, VFT) of central obesity and transrectal total prostate volume suggests a protective effect. We can therefore deduce from our study that the presence, absence, and nature of association between obesity and prostate volume could be dependent on the indices of obesity studied. Our study suggests that while generalized obesity is a risk factor for enlargement of the transitional zone, abdominal fat may actually protect against enlargement of the transitional zone.

A limitation to our study is the fact we assessed abdominal fat with USS rather than CT or MRI as USS is operator-dependent and its reproducibility is therefore poor.[5] However, the use of USS to assess abdominal fat in this study provided a different perspective to the understanding of the relationship between adiposity and BPE in our hospital. Bearing in mind that there could be population differences due to dietary differences or genetic variations, larger community-based and longitudinal studies are recommended to further define the association between obesity and BPE to aid our understanding for focused therapeutic approaches.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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