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|Benign prostatic hyperplasia|
|Classification and external resources|
Diagram illustrating normal prostate (left) and benign prostatic hyperplasia (right).
|Benign prostatic hyperplasia|
|Classification and external resources|
Diagram illustrating normal prostate (left) and benign prostatic hyperplasia (right).
Benign prostatic hyperplasia (BPH), also called benign enlargement of the prostate (BEP), adenofibromyomatous hyperplasia and benign prostatic hypertrophy (technically incorrect usage), is an increase in size of the prostate.
BPH involves hyperplasia of prostatic stromal and epithelial cells, resulting in the formation of large, fairly discrete nodules in the periurethral region of the prostate. When sufficiently large, the nodules compress the urethral canal to cause partial, or sometimes virtually complete, obstruction of the urethra, which interferes with the normal flow of urine. It leads to symptoms of urinary hesitancy, frequent urination, dysuria (painful urination), increased risk of urinary tract infections, and urinary retention. Although prostate specific antigen levels may be elevated in these patients because of increased organ volume and inflammation due to urinary tract infections, BPH does not lead to cancer or increase the risk of cancer.
BPH involves hyperplasia (an increase in the number of cells) rather than hypertrophy (a growth in the size of individual cells), but the two terms are often used interchangeably, even amongst urologists.
Adenomatous prostatic growth is believed to begin at approximately age 30 years. An estimated 50% of men have histologic evidence of BPH by age 50 years and 75% by age 80 years; in 40–50% of these men, BPH becomes clinically significant.
Benign prostatic hyperplasia symptoms are classified as storage or voiding.
Storage symptoms include urinary frequency, urgency (compelling need to void that cannot be deferred), urgency incontinence, and voiding at night (nocturia).
Voiding symptoms include urinary stream hesitancy (needing to wait for the stream to begin), intermittency (when the stream starts and stops intermittently), straining to void, and dribbling. Pain and dysuria are usually not present. These storage and voiding symptoms are evaluated using the International Prostate Symptom Score (IPSS) questionnaire, designed to assess the severity of BPH.
BPH can be a progressive disease, especially if left untreated. Incomplete voiding results in stasis of bacteria in the bladder residue and an increased risk of urinary tract infection. Urinary bladder stones are formed from the crystallization of salts in the residual urine. Urinary retention, termed acute or chronic, is another form of progression. Acute urinary retention is the inability to void, while in chronic urinary retention the residual urinary volume gradually increases, and the bladder distends. This can result in bladder hypotonia. Some patients that suffer from chronic urinary retention may eventually progress to renal failure, a condition termed obstructive uropathy.
Most experts consider androgens (testosterone and related hormones) to play a permissive role. This means that androgens have to be present for BPH to occur, but do not necessarily directly cause the condition. This is supported by the fact that castrated boys do not develop BPH when they age. On the other hand, administering exogenous testosterone is not associated with a significant increase in the risk of BPH symptoms. Dihydrotestosterone (DHT), a metabolite of testosterone, is a critical mediator of prostatic growth. DHT is synthesized in the prostate from circulating testosterone by the action of the enzyme 5α-reductase, type 2. This enzyme is localized principally in the stromal cells; hence, those cells are the main site for the synthesis of DHT.
DHT can act in an autocrine fashion on the stromal cells or in paracrine fashion by diffusing into nearby epithelial cells. In both of these cell types, DHT binds to nuclear androgen receptors and signals the transcription of growth factors that are mitogenic to the epithelial and stromal cells. DHT is 10 times more potent than testosterone because it dissociates from the androgen receptor more slowly. The importance of DHT in causing nodular hyperplasia is supported by clinical observations in which an inhibitor of 5α-reductase such as finasteride is given to men with this condition. Therapy with a 5α-reductase inhibitor markedly reduces the DHT content of the prostate and, in turn, reduces prostate volume and, in many cases, BPH symptoms.
Testosterone promotes prostate cell proliferation, but relatively low levels of serum testosterone are found in patients with BPH. One small study has shown that medical castration lowers the serum and prostate hormone levels unevenly, having less effect on testosterone and dihydrotestosterone levels in the prostate.
While there is some evidence that estrogen may play a role in the etiology of BPH, this effect appears to be mediated mainly through local conversion of androgens to estrogen in the prostate tissue rather than a direct effect of estrogen itself. In canine in vivo studies castration, which significantly reduced androgen levels but left estrogen levels unchanged, caused significant atrophy of the prostate. Studies looking for a correlation between prostatic hyperplasia and serum estrogen levels in humans have generally shown none.
In 2008, Yigal Gat et al. published evidence that BPH is caused by failure in the spermatic venous drainage system resulting in increased hydrostatic pressure and local testosterone levels elevated more than 100 fold above serum levels. If confirmed, this mechanism explains why serum androgen levels do not seem to correlate with BPH and why giving exogenous testosterone would not make much difference. This also has implications for treatment (see Minimally invasive therapies below).
On a microscopic level, BPH can be seen in the vast majority of men as they age, in particular over the age of 70 years, around the world. However, rates of clinically significant, symptomatic BPH vary dramatically depending on lifestyle. Men that lead a western lifestyle have a much higher incidence of symptomatic BPH than men that lead a traditional or rural lifestyle. This is confirmed by research in China showing that men in rural areas have very low rates of clinical BPH, while men living in cities adopting a western lifestyle have a skyrocketing incidence of this condition, though it is still below rates seen in the West.
Much work remains to be done to completely clarify the causes of BPH.
Both the glandular epithelial cells and the stromal cells (including muscular fibers) undergo hyperplasia in BPH.:694 Most sources agree that of the two tissues, stromal hyperplasia predominates, but the exact ratio of the two is unclear.:694
Anatomically, BPH is most strongly associated with the posterior urethral glands (PUG) and transitional zone (TZ) of the prostate. The earliest microscopic signs of BPH usually begin between the age of 30 and 50 years old in the PUG, which are posterior to the proximal urethra.:694 However, the majority of growth eventually occurs in the TZ.:694 In addition to these two classic areas, the peripheral zone (PZ) of the prostate is also involved to a lesser extent.:695 Since prostatic cancer also occurs in the PZ, BPH nodules in the PZ are often biopsied to rule out cancer.:695
Often, blood tests are performed to rule out prostatic malignancy: Elevated prostate specific antigen (PSA) levels needs further investigations such as reinterpretation of PSA results, in terms of PSA density and PSA free percentage, rectal examination and transrectal ultrasonography. These combined measures can provide early detection.
Patients should decrease fluid intake before bedtime, moderate the consumption of alcohol and caffeine-containing products, and follow timed voiding schedules.
Antimuscarinics such as tolterodine may also be used, especially in combination with alpha blockers. They act by decreasing acetylcholine effects on the smooth muscle of the bladder, thus helping control symptoms of an overactive bladder.
Sildenafil citrate shows some symptomatic relief, suggesting a possible common etiology with erectile dysfunction. Tadalafil was considered then rejected by NICE in the UK for the treatment of symptoms associated with BPH.
The European Urology Review published in 2009 that two Israeli doctors, Yigal Gat and Menahem Goren, have developed the Gat-Goren nonsurgical method for BPH. Using an interventional radiological technique that reduces prostate volume and reverses BPH symptoms, the treatment, known as super-selective intra-prostatic androgen deprivation (SPAD) therapy, involves a percutaneus venography and sclerotherapy of the internal spermatic vein network, including associated venous bypasses and retroperitoneal collaterals. The European Urology Review also declared that using the Gat Goren nonsurgical method results in decreased prostate volume, which leads to significantly decreased nocturia, improved urine stream, and also improves emptying of the urinary bladder, and that without the potential side effects and complications of the classic surgery.
Medication is often prescribed as the first treatment option, there are many patients who do not achieve success with this line of treatment. Those patients may not achieve sustained improvement in symptoms or they may stop taking the medication because of side-effects. There are options for treatment in a urologist's office before proceeding to surgery. The two most common types of office-based therapies are transurethral microwave thermotherapy (TUMT) and transurethral needle ablation (TUNA). Both of these procedures rely on delivering enough energy to create sufficient heat to cause cell death (necrosis) in the prostate. The goal of the therapies is to cause enough necrosis so that, when the dead tissue is reabsorbed by the body, the prostate shrinks, relieving the obstruction of the urethra. These procedures are typically performed with local anesthesia, and the patient returns home the same day. Some urologists have studied and published long-term data on the outcomes of these procedures, with data out to five years. The most recent American Urological Association (AUA) Guidelines for the Treatment of BPH in 2003 lists minimally invasive therapies including TUMT and TUNA as acceptable alternatives for certain patients with BPH.
Transurethral microwave therapy (TUMT) was originally approved by the United States Food and Drug Administration (FDA) in 1996, with the first generation system by EDAP Technomed. Since 1996, other companies have received FDA approval for TUMT devices, including Urologix, Dornier, Thermatrix, Celsion, and Prostalund. Multiple clinical studies have been published on TUMT. The general principle underlying all the devices is that a microwave antenna that resides in a urethral catheter is placed in the intraprostatic area of the urethra. The catheter is connected to a control box outside of the patient's body and is energized to emit microwave radiation into the prostate to heat the tissue and cause necrosis. It is a one-time treatment that takes approximately 30 minutes to 1 hour, depending on the system used. It takes approximately 4 to 6 weeks for the damaged tissue to be reabsorbed into the patient's body. Some of the devices incorporate circulating coolant through the treatment area with the intent of preserving the urethra while the microwave energy heats the prostatic tissue surrounding the urethra.
Transurethral needle ablation (TUNA) operates with a different type of energy, radio frequency (RF) energy, but is designed along the same premise as TUMT devices, that the heat the device generates will cause necrosis of the prostatic tissue and shrink the prostate. The TUNA device is inserted into the urethra using a rigid scope much like a cystoscope. The energy is delivered into the prostate using two needles that emerge from the sides of the device, through the urethral wall and into the prostate. The needle-based ablation devices are very effective at heating a localized area to a high enough temperature to cause necrosis. The treatment is typically performed in one session, but may require multiple sticks of the needles depending on the size of the prostate.
If medical treatment fails, and the patient elects not to try office-based therapies or the physician determines the patient is a better candidate for transurethral resection of prostate (TURP), surgery may need to be performed. In general, TURP is still considered the gold standard of prostate interventions for patients that require a procedure. This involves removing (part of) the prostate through the urethra. There are also a number of new methods for reducing the size of an enlarged prostate, some of which have not been around long enough to fully establish their safety or side-effects. These include various methods to destroy or remove part of the excess tissue while trying to avoid damaging what remains. Transurethral electrovaporization of the prostate (TVP), laser TURP, visual laser ablation (VLAP), ethanol injection, and others are studied as alternatives.
Newer techniques involving lasers in urology have emerged in the last 5–10 years, starting with the VLAP technique involving the Nd:YAG laser with contact on the prostatic tissue. A similar technology called Photoselective Vaporization of the Prostate (PVP) with the GreenLight (KTP or LBO crystal) laser have emerged very recently. This procedure involves a high-power 180-watt 532 nm wavelength laser with a 650-micrometre laser fiber inserted into the prostate. This fiber has an internal reflection with a 70-degree deflecting angle. It is used to vaporize the tissue to the prostatic capsule. GreenLight 532 nm lasers target haemoglobin as the chromophore and typically have a penetration depth of 0.8mm (two times deeper than holmium).
Another procedure termed Holmium Laser Ablation of the Prostate (HoLAP) has also been gaining acceptance around the world. Like KTP, the delivery device for HoLAP procedures is a 550 um disposable side-firing fiber that directs the beam from a high-power 100-watt laser at a 70-degree angle from the fiber axis. The holmium wavelength is 2,140 nm, which falls within the infrared portion of the spectrum and is invisible to the naked eye. Whereas GreenLight relies on haemoglobin as a chromophore, water within the target tissue is the chromophore for Holmium lasers. The penetration depth of Holmium lasers is <0.4 mm, avoiding complications associated with tissue necrosis often found with the deeper penetration and lower peak powers of Nd:YAG lasers used in the 1990s.
HoLEP, Holmium Laser Enucleation of the Prostate, is another Holmium laser procedure reported to carry fewer risks compared with either TURP or open prostatectomy. HoLEP is largely similar to the HoLAP procedure; the main difference is that this procedure is typically performed on larger prostates. Instead of ablating the tissue, the laser cuts a portion of the prostate, which is then cut into smaller pieces and flushed with irrigation fluid. As with the HoLAP procedure, there is little bleeding during or after the procedure.
Both wavelengths, GreenLight and Holmium, ablate approximately one to two grams of tissue per minute.
People often seek herbal remedies for BPH. Several are approved in European countries, but none in the USA. Saw palmetto extract from Serenoa repens is one of the most extensively studied. It showed promise in early studies, though later trials of higher methodological quality have had mixed results.
Other herbal medicines that have research support in systematic reviews include beta-sitosterol from Hypoxis rooperi (African star grass) and pygeum (extracted from the bark of Prunus africana), while there is less substantial support for the efficacy of pumpkin seed (Cucurbita pepo) and stinging nettle (Urtica dioica) root. There is weak evidence that pollen extracts from rye grass (Secale cereale) may also correlate with modest symptomatic relief.
Globally, benign prostatic hyperplasia affects about 210 million males as of 2010 (6% of the population). The prostate gets larger in most men as they get older. For a symptom-free man of 46 years, the risk of developing BPH over the next 30 years is 45%. Incidence rates increase from 3 cases per 1000 man-years at age 45–49 years, to 38 cases per 1000 man-years by the age of 75–79 years. While the prevalence rate is 2.7% for men aged 45–49, it increases to 24% by the age of 80 years.
For some men, the symptoms may be severe enough to require treatment.
Christensen, Tyler L.; Andriole, Gerald L. (February 2009). "Benign Prostatic Hyperplasia: Current Treatment Strategies". Consultant 49 (2): 115–22. http://www.consultantlive.com/prostate-cancer/content/article/10162/1376744.
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