Prostatitis Syndromes. Part 4: Diagnosis
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Cultures. In acute cases, documentation of a significant infection of the bladder urine is all that is required for definitive diagnosis. However, a urine culture is insufficient to differentiate chronic bacterial prostatitis from non-bacterial prostatitis or prostatodynia, as specimens are usually sterile in all three disorders. Culture evidence of prostatic infection is necessary to accurately diagnose bacterial prostatitis in the chronic stage.
The absolute key to diagnosis of chronic prostatitis is investigation of expressed prostatic secretion or, if this cannot be obtained, of seminal fluid. (If acute infection of the prostate gland is suspected, expressed prostatic secretions should not be obtained, as the patient could become septic.) Microscopic examination of the expressed prostatic secretion is extremely helpful. Excessive leukocytes (more than 10 per high-power field in an unspun specimen) and macrophages containing fat or oval fat bodies indicate prostatic inflammation. However, other genitourinary conditions, such as urethritis, urethral condylomata, and strictures, can also cause excessive leukocytosis in the expressed prostatic secretion.
Microscopic examination of seminal fluid, which usually can be collected more easily and certainly in larger volumes than the expressed prostatic secretion (EPS), can be misleading because of the difficulty of determining leukocytosis in the specimen. Immature sperm cells in unstained or conventionally stained samples look very much like leukocytes and limit the practical value of microscopic analysis. Moreover, the impact of prostatic inflammation on seminal fluid leukocyte density is really unknown.
The most accurate way to diagnose bacterial pathogenesis is to employ specific cultures. These simultaneous, quantitative bacterial cultures of urethral urine, bladder urine, and expressed prostatic secretion (Figure 2) are extremely important, especially on the first presentation. Physicians need a working understanding of the rationale and interpretation of this method to manage chronic prostatitis syndromes. Because prostatic fluid is subject to contamination by bacteria that colonize the urethra, one must determine the origin of the prostatic fluid isolates.
Figure 2. Segmented Cultures of the Lower Urinary Tract in Men
The first 5 to 10 mL of urine collected after retracting the foreskin and thoroughly cleaning the glans penis is labelled as VB1, or voided bladder 1. The second collection is similar to a midstream urine sample (MSSU) and is labelled VB2. The physician then massages the prostate gland while collecting or having the patient collect the drops of expressed prostatic secretion emitting from the urethral meatus. After the EPS has been collected, the residual drop along the urethra is used to prepare a slide for microscopic examination as previously described. The patient is then asked to void again, and the VB3 is collected in the same manner as VB1. While a high bacterial count in the EPS strongly suggests chronic bacterial prostatitis, the definitive diagnosis is confirmed when a quantitative count demonstrates a significantly higher number of bacteria per mL in the prostatic fluid than in VB1 or in the midstream VB2 specimen (Figure 3). If EPS is impossible to obtain, a significantly higher bacterial count in the VB3, which should contain some prostatic expressate, may be suggestive.
Figure 3. Diagnostic Algorithm For The Prostatitis Syndromes
If EPS is impossible to obtain, a culture of the ejaculate, which does contain prostatic secretions, may be performed. Because the ejaculate must pass through the urethra and can be contaminated by urethral organisms, a concomitant study of urethral (VB1) and bladder (VB2) specimens is required. Comparisons of the three specimens must show an excessive bacterial count in the seminal fluid.
When non-bacterial prostatitis is suggested by leukocytosis in a sterile prostatic secretion, one can obtain specific cultures for chlamydia and mycoplasma. This is not routinely done at present and remains a research tool. Unfortunately most patients have not undergone such a rigorous work-up before therapy. It is very frustrating to attempt to properly diagnose and treat patients after they have been on a number of antibiotics for various durations. It is a good idea with such a patient to discontinue antibiotics for at least 6 weeks and repeat the segmented cultures as described. If this procedure does not localize the bacterial pathogen, and previous history or previous cultures still make the physician suspect chronic bacterial prostatitis, I would recommend proceeding (with the patient’s consent) to an ultrasound-guided percutaneous aspiration biopsy of the prostate gland. Because infection is likely very focal, sampling errors are inevitable, and this does not present an ideal diagnostic test.
When other causes are excluded.If all these investigations have failed to disclose a pathogen and the patient has failed to respond to a trial course of antibiotics for either bacterial or non-bacterial organisms, the disorder is categorized as non-bacterial prostatitis (if inflammation is present) or prostatodynia (if it is not).
It cannot be overemphasized that a rigorous diagnostic routine, as described in this section, is mandatory for the prostatitis syndromes, especially at first presentation. Proper diagnosis will reduce frustration for both patient and physician and lead to a more rewarding outcome.