Abstract: In benign prostatic hyperplasia (BPH), the lower urinary tract changes both functionally and organically in association with the enlargement of prostate. Thereby, lower urinary tract symptoms (LUTS) are manifested. LUTS are classified into symptoms in the storage phase and in the voiding phase. The former includes urinary frequency, nocturia, urinary urgency, and incontinence. These are caused by detrusor enlargement and increased bladder sensation which occur in association with urethral resistance increased by urethral compression resulting from BPH. The symptoms caused by difficult voiding due to urethral compression by enlarged prostate are called voiding symptoms, which include urinary hesitation, prolongation of micturition time, weakening of stream, and so on. Aging, cerebral disease, vertebral disease, spinal disease, and heart disease present lower urinary tract symptoms very similar to those associated with BPH and these diseases complicate symptoms of BPH

C Nakajima

Kosaku Yasuda

Masataka Yano

Satoshi Kitahara

T Yamanishi

Y Iimura

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* This article is a revised English version of a paper originally published in the Journal of the
Japan Medical Association (Vol. 123 No. 2, 2000, pages 205–209). The Japanese text is a
transcript of a lecture originally aired on September 21, 1999, by the Nihon Shortwave
Broadcasting Co., Ltd., in its regular program “Special Course in Medicine”.
** Department of Urology, Dokkyo University School of Medicine, Koshigaya Hospital
*** Department of Urology, Chiba University, School of Medicine
91
THE REASON WHY PROSTATIC HYPERPLASIA
CAUSES LOWER URINARY TRACT SYMPTOMS*
Masataka YANO**, Kosaku YASUDA**, Satoshi KITAHARA**,
C. NAKAJIMA**, Y. IIMURA**, and T. YAMANISHI***
Asian Med. J. 44(2): 91–96, 2001
Abstract: In benign prostatic hyperplasia (BPH), the lower urinary tract changes
both functionally and organically in association with the enlargement of prostate.
Thereby, lower urinary tract symptoms (LUTS) are manifested. LUTS are classified
into symptoms in the storage phase and in the voiding phase. The former includes
urinary frequency, nocturia, urinary urgency, and incontinence. These are caused by
detrusor enlargement and increased bladder sensation which occur in association
with urethral resistance increased by urethral compression resulting from BPH. The
symptoms caused by difficult voiding due to urethral compression by enlarged pros-
tate are called voiding symptoms, which include urinary hesitation, prolongation of
micturition time, weakening of stream, and so on. Aging, cerebral disease, vertebral
disease, spinal disease, and heart disease present lower urinary tract symptoms very
similar to those associated with BPH and these diseases complicate symptoms of
BPH.
Key words: Benign prostatic hyperplasia; Lower urinary tract symptoms;
Storage symptoms; Voiding symptoms
Introduction
Benign prostatic hyperplasia (BPH) is fundamentally a disease that causes
morbidity through the urinary symptoms with which it is associated.1) Symptoms
related to micturition are called lower urinary tract symptoms (LUTS),2) which are
classified into those which occur in the storage phase (storage symptoms) and
those which occur in the voiding phase (voiding symptoms). The former includes
urinary frequency, urinary urgency, nocturia (3 or more times voiding at night), and
urinary incontinence. The latter includes micturition pain, hesitation, prolongation
of voiding, interruptions of voiding, weak stream, sensation of residing straining
for voiding, and terminal dribbling.
Most LUTS are characteristic of various lower urinary tract diseases, espe-
M. YANO et al. Asian Med. J. 44(2), 200192
Table 1 International Prostate Symptom Score (I-PSS)
Not Less than Less than About half More than Almost
at all 1 time in 5 half the time the time half the time always
1. Over the past month or so, how often
have you had a sensation of not emptying
your bladder completely after you 0 1 2 3 4 5
finished urinating?
2. Over the past month or so, how often
have you had to urinate again less than 0 1 2 3 4 5
two hours after you finished urinating?
3. Over the past month or so, how often
have you found you stopped and started 0 1 2 3 4 5
again several times when you urinated?
4. Over the past month or so, how often
have you found it difficult to postpone 0 1 2 3 4 5
urination?
5. Over the past month or so, how often
have you had a weak urinary stream? 0 1 2 3 4 5
6. Over the past month or so, how often
have you had to push or strain to begin 0 1 2 3 4 5
urination?
7. Over the last month, how many times 5 or
did you most typically get up to urinate None 1 time 2 times 3 times 4 times more
from the time you went to bed at night  times
until the time you got up in the morning?
0 1 2 3 4 5
I-PSSsum of questions 1–7
Quality of life due to urinary symptoms
If you were to spend the Mostly Mixed (about Mostlyrest of your life with your Delighted Pleased equally satisfied Unhappy Terrible
urinary condition just the satisfied and dissatisfied) dissatisfied
way it is now, how would
you feel about that? 0 1 2 3 4 5 6
Reference: Barry M.J., Fowler, F.J., O’Leary, M.P. et al.: the American Urological Association Symptom Index for
benign prostatic hyperplasia. J Urol 148: 1549, 1992.
cially bladder outlet obstructions. BPH also has several characteristic symptoms.
WHO has recommended the use of a standard called “International Prostate
Symptom Score (IPSS)”, which scores the seven listed symptoms, for severity
judgement3) (Table 1). However, it has already been proven that this scoring stan-
dard is not sufficient to estimate or judge the volume of the prostate (benign
prostatic enlargement: BPE) or the degree of lower urinary tract obstruction.4)
In this review we discuss the mechanism by which BPE causes LUTS and the
reason why BPH cannot be exactly diagnosed from these symptoms in cases with
BPE.
Mechanism Through Which BPE Causes LUTS
An enlarged prostate oppresses the urethra, or obstructs it, and increases
urethral resistance and the work of the detrusor for micturition. This results in
THE REASON WHY BPH CAUSES LUTS 93
detrusor hypertrophy. As urethral obstruction progresses, the postvoid residual
urine volume increases. That is, to whatever extent the detrusor hypertrophies, it
cannot void urine sufficiently, and the condition becomes decompensatory (Table
2). LUTS are manifested due to such lower urinary tract changes associated with
BPE. Thus the manifested symptoms are considered to be specific urinary symp-
toms to BPE.
BPE obstructs the urethra, and, thereby, a voiding disturbance occurs. This is
also fundamentally important in BPH. The above mentioned voiding symptoms,
such as hesitancy, prolongation, weak stream, etc., are found in 60–90% of BPH
patients. In our experience, hesitancy is the most important of the voiding symp-
toms in BPH. We explain the reason below.5)
The possible mechanisms of bladder outlet obstruction due to BPE are (1) the
enlargement of the prostate resulting in extension of the urethra and prostatic
capsule and (2) the increase in tonus of the smooth muscle in the prostate.6) As is
well known, in the drug therapy of BPH, an anti-androgen is used to reduce the
size of the gland and an -blocker to decrease smooth muscle tone.7) Our series of
studies have demonstrated that an -blocker not only decreases smooth muscle
tone but also resolves detrusor bladder neck dyssynergia in the voiding phase.
When the detrusor contracts, the -blocker makes the internal urethral orifice
open synchronously.
As bladder outlet obstruction progresses due to BPE, the detrusor sensitivity
to the stimulus increases and, in this condition, the bladder contracts suddenly
even when a small amount of urine, with which no desire to void occurs in normal
conditions, accumulates in the bladder. This condition is called detrusor over-
activity, or unstable bladder. Unstable bladder causes urinary urgency or urge
incontinence. Urinary incontinence is a troublesome condition and the patient
frequently goes to the toilet.
Hypertrophy of the detrusor results in bladder wall thickening due to which
Table 2 Mechanism of Urinary Tract Disturbance in BPH
1. Voiding disturbance
A. Organic (BPE)
1) Obstruction
2) Compression of the external urethral sphincter
3) Extension of the prostatic capsule
4) Compression of the bladder base
5) Elongation of the prostatic urethra
B. Functional
1) Increase in -receptor in the prostate
2) Detrusor bladder neck dyssynergia
3) Inability of the external urethral sphincter
4) Dyscontractility of the detrusor due to bladder distension
2. Storage disturbance
A. Organic (Low compliance bladder)
B. Functional
1) Detrusor overactivity
2) Overdistension of the detrusor
the detrusor smooth muscle cannot stretch smoothly in the storage phase. Such a
condition is called low-compliance bladder. In this condition, not much urine can
be held in the bladder and urinary frequency occurs. It has been reported that
benign prostatic enlargement (BPE) causes extension of the urethra and prostatic
capsule, and sensory nerves present in the capsule are stimulated. Unstable blad-
der is thus induced in the filling phase. In our experience, urinary frequency and
nocturia are the most important of the storage symptoms in BPH. In the stage of
decompensation of the detrusor, intravesical pressure increases due to bladder wall
thickening and large postvoid residual urine volume, and urine cannot be trans-
ferred to the bladder through the ureter. In this condition, hydroureter and
hydronephrosis lead to chronic postrenal failure advance.8) As such a condition
advances, voiding symptoms increase in severity and large residual urine volume
is found in the bladder. Urine cannot be voided without straining. In patients
having a lot of postvoid residual urine due to difficulty in voiding, an abdominal
pressure by turning over in bed or in standing up sometimes causes urinary incon-
tinence which is a symptom in the storage phase. This is called overflow inconti-
nence. In addition, abdominal distension associated with residual urine and hydro-
nephrosis and edema due to renal failure also occur. As mentioned above, BPH
triggers so many urinary symptoms that it is difficult to determine which symptoms
are specific to BPH.
Other Factors Complicating BPH Symptoms or
Causing Similar Symptoms
The prostate becomes enlarged at the age of 40 years or later. Age-associated
urinary disturbance may sometimes change BPH symptoms or cause similar symp-
toms. Factors complicating BPH symptoms include the aging of lower urinary tract
tissue, changes in urine-producing circadian rhythm due to changes in vasopressin
secretion, lower limb edema due to cardiac dysfunction, vertebral or spinal dis-
eases, cerebral infarction and so on (Table 3).
The change in urinary symptoms by aging is a significant factor which alters
BPH-specific symptoms. A change in the lower urinary tract which arises through
aging is the aging of the bladder. The aging of the bladder causes a degeneration
of detrusor tissue, resulting in the formation of more junctions between smooth
Table 3 Other Factors Complicating BPH Symptoms
or Causing Similar Symptoms
1. Detrusor hyperactivity with incomplete contraction
2. Cardiac disease
3. Renal failure
4. Cerebral infarction
5. Vertebral or spinal cord disease
6. Bladder neck obstruction
7. Prostatitis
8. Others
M. YANO et al. Asian Med. J. 44(2), 200194
muscles. Thus, the detrusor becomes overactive (unstable bladder). In this condi-
tion, a minimal stimulus to the bladder (small volume of urine) causes detrusor
contraction. Unstable bladder is a major cause of urinary frequency, urgency and
urinary incontinence. Fibrous tissue deposits between the detrusor muscle and,
thereby, the bladder cannot dilate smoothly and it becomes difficult to fill with
urine. This condition is low-compliance bladder, which becomes causative of uri-
nary frequency. On the other hand, detrusor degeneration leads to the reduction
in bladder contraction and induces voiding symptoms such as prolongation of
micturition time, weakening of stream, etc.
Due to the above reasons, detrusor hyperactivity with incomplete contraction
(DHIC) is often found in elderly people.9) In DHIC, unstable bladder generally co-
exists with detrusor incomplete contraction. It has been known that the incidence
of this phenomenon increases remarkably at the age of 70 years. In DHIC, storage
disturbance such as urinary frequency and urinary incontinence is found together
with voiding disturbance such as increased postvoid residual urine volume. In the
presence of increased residual urine volume, urinary tract infection is often found.
This condition is very similar to lower urinary tract symptoms in BPH. In other
words, the same lower urinary tract symptoms as those in BPH occur even in BPH-
free females aged over 70 years.
It is well known that circadian rhythm of vasopressin secretion changes with
aging. The decrease in vasopressin secretion at night leads to nocturnal polyuria,
which causes nocturia.
In heart disease with lower limb edema, the volume of circulating blood
increases during night sleeping and urine volume increases at night. This causes
nocturia.
In vertebral or spinal disease and cerebral infarction, it is likely that voiding-
related central nervous system may be damaged. This is called neurogenic bladder.
The most common phenomenon is detrusor overactivity (detrusor hyperreflexia)
which is caused by supra-nuclear lesion of nerves innervating the detrusor. Like
unstable bladder in BPH, this condition causes urinary urgency or urge inconti-
nence. In spinal disease, detrusor-sphincter dyssynergia is often found. In this con-
dition, the external urethral sphincter contracts to close the urethra when the
detrusor contracts and, thus, voiding is disturbed. This voiding symptom due to
non-synergic contraction of the external urethral sphincter is similar to urethral
obstruction due to BPH.
Conclusion
In BPH, the lower urinary tract changes both functionally and organically
in association with the enlargement of prostate. Thereby, LUTS are manifested.
LUTS are classified into symptoms in the storage phase and those in the voiding
phase. The former includes urinary frequency, nocturia, urinary urgency, and incon-
tinence. These symptoms are caused by detrusor enlargement and increased blad-
der sensation which occur in association with urethral resistance increased by ure-
thral compression resulting from BPH. The symptoms caused by difficult voiding
due to urethral compression by enlarged prostate are called voiding symptoms and
THE REASON WHY BPH CAUSES LUTS 95
include urinary hesitation, prolongation of micturition time, weakening of stream,
etc.
In this article, the authors have pointed out that aging, cerebral disease, ver-
tebral disease, spinal disease, and heart disease present lower urinary tract symp-
toms very similar to those associated with BPH and also that these diseases com-
plicate symptoms of BPH.
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M. YANO et al. Asian Med. J. 44(2), 200196


THE REASON WHY PROSTATIC HYPERPLASIA CAUSES LOWER URINARY TRACT SYMPTOMS*

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