Introduction

Benign prostatic hyperplasia(BPH) is a common condition among men¹ and surgery for this condition is the second most common major operation for medicare in aged men (after cataract surgery)². It is a pathological process that contributes to, but is not the only cause of lower urinary tract symptoms in ageing men.

Estimation of prostate volume may be useful in a variety of clinical settings. It is generally accepted though, that there is a minimal direct correlation between prostate volume and symptoms of BPH^{3, 4}. Measurement of prostate volume is valuable in medical treatment of BPH as well; for example large prostates (total prostate volume more than 40mls) may respond better with 5 alpha reductase inhibitors while there is good clinical effect on smaller prostates with alpha blockers ^{5, 6}. Measurement of prostate volume though most accurate with trans- rectal ultrasound (TRUS); results from measurements done by transabdominal ultrasound correlate well with that of TRUS ⁷.

Additionally, prostate volume can help in the interpretation of serum prostate specific antigen⁸. Serum PSA has been shown to correlate with prostate volume among white men without prostate cancer; thus nomograms for predicting prostate volume from serum PSA have been developed⁹. Moreover, some authorities suggest that PSA can be used to predict the therapeutic efficacy of treatment modalities for BPH on the grounds that PSA and prostate volume are correlated ^10,11. Most data on the correlation between PSA and prostate volume have been obtained from western populations. Unfortunately, very few studies have been done among African men; more so, with the findings in Japanese men that they release more PSA per unit prostate tissue than white men¹².It became imperative for us to carry out a prospective study to determine the correlation between PSA and prostate volume among Nigerian men.

Patients, Materials and Methods

This study was carried out in Jos University Teaching Hospital (JUTH), a tertiary health institution located in the heart of Jos the Plateau state capital. Plateau state is located in the central part of Northern Nigeria. This hospital receives referral for surgical and other health problems from Plateau state and neighboring states such as Nassarawa, Benue, Taraba, Adamawa, Bauchi, Gombe and Kaduna.

A total of 120 patients who were pathologically diagnosed with BPH by transrectal trucut biopsy specimen of the prostate at the outpatient clinic of Jos University Teaching Hospital from 2006 to2008 were included in the study. The reasons for biopsy were increased PSA (>4ng/ml) or abnormal digital rectal examination. Those with biopsy evidence of prostate cancer, prostatitis, prostatic intraepithelial neoplasia or atypical small acinar proliferation detected at any point during follow up were excluded from the study. We also excluded those who have received any form of medical, minimally, invasive or open surgical treatments.

The total prostate volume was measured by a consultant radiologist using a transabdominal ultrasound (GE Logics Expert 052128 model). The total prostate volume was calculated using the formula V=α×β×γ×π\6 (prolate ellipsoid formula). The PSA was determined by ELISA. Factors affecting PSA like trucut prostate biopsy, urinary tract infection, the use of finesteride, transurethral instrumentation and vigorous prostate digital examination were excluded.

Results

As shown in Table 1, the mean age for the patients was 65.6±9.84 years. The maximum age of the patient enrolled for the study was 85 years. The maximum PSA value recorded in the study was 35ng/ml, though the mean PSA was 12.44±15.49 ng/ml. The maximum total prostate volume was 223.82mls. The correlation between age and PSA is 0.026 based on the Pearson’s correlation co efficient (P>0.05) as shown in figure 1

The correlation between total prostate volume and PSA is 0.3365 based on the Pearson’s correlation co efficient (P<0.05) as shown in figure 2.

Figure 1

Table 1: Descriptive statistics on all 120 patients

Figure 2

Figure 1: Scatter plot of Age and PSA

Figure 3

Figure 2: Scatter plot of prostate volume and PSA

Discussion

The pathophysiology of clinical BPH has been attributed to bladder outlet obstruction secondary to prostatic enlargement¹³. Imaging modalities have been applied in estimating prostate size however; PSA is usually evaluated in patients with BPH as further evaluation to determine those that would benefit from prostate biopsy.

This study determined the correlation between serum PSA and prostate volume in Nigerian men with biopsy proven benign prostatic hyperplasia. The value of the mean prostate volume (72.79±44.38mls) in this study differed from a similar study on determination of prostate volume done by Ibinaye¹⁴ on Nigerian men (46.62±21.56mls). This difference may be attributed to numerical bias; more patients were enrolled in our study compared to theirs. However, when compared to prostate volume values obtained in Europe and America in which a range of 30.3±9.8 to 49.0±26.9 was obtained¹⁵, there was significant difference which could be explained by the late presentation of Africans to the clinic compared to the Caucasians. The mean PSA value compared to normal PSA range was elevated. This may be attributed to the mean prostate volume in this study which was high; since there is a correlation between PSA and prostate volume, the elevated mean PSA could be explained by this finding.

The study also showed that there was a statistically significant correlation between serum PSA and prostate volume in Nigerian men. This study agreed with the findings of Hochberg et al¹⁶ which pointed out that in patients with BPH proven by TRUS biopsy, PSA and prostate volume had a statistically significant correlation.

In addition, there was no significant correlation between age and PSA in our study. This result differs from that obtained among caucascians¹⁷. The difference may be attributed to a selection bias. The age of our patients was not evenly distributed across the age range; about 42% of the patients were aged between 70-85 years old. The uneven age distribution may have accounted for the difference in statistical analysis. There is a possibility that if we had enrolled more patients who were older the correlation between age and PSA might have become significant. This finding although differed from that noted by Sang Eun Lee et al¹⁸, agreed with what Yu-Lung Chang et al¹⁷ observed in their study of Taiwanese men.

Conclusion

In Nigerian men with biopsy proven BPH, the volume of the prostate significantly correlated with serum PSA. There was no significant correlation between age and PSA. These findings agreed with that of Taiwanese men.

Furthermore, interpretation of serum PSA result in Nigerian men should be done with caution, since generally, they present with large prostate volume which may influence the value of the PSA.. When in doubt, a PSA density should be done and if it is elevated, a prostate biopsy should be done