AssessmentsUrinary incontinence: Pathology review
USMLE® Step 1 style questions USMLE
A 75 year-old African-American male comes to the office because of continuous dribbling of urine which began one month ago. In addition, the patient endorses difficulty initiating and maintaining a urinary stream. Past medical records indicate that he has hypertension and type 2 diabetes mellitus. The patient has a 40-pack-year smoking history. His temperature is 37.0°C (98.6°F), blood pressure is 150/86 mmHg, pulse is 70/min, and respirations are 15/min. Cardiac, pulmonary, and abdominal examinations are non-contributory. Digital rectal exam reveals an enlarged, symmetrical, and smooth prostate. Laboratory study results are as follows:
*Normal PSA < 4.0 ng/ml
Laboratory value Result Glucose 118 mg/dL HbA1c 6.9% Prostate-specific antigen (PSA)* 3.6 ng/ml
Which of the following is the most likely cause of the patient’s urinary symptoms?
Content Reviewers:Yifan Xiao, MD
In the Urology ward, two people are coming in. The first is Oleg, a 70 year old man who says that he frequently has to use the bathroom and also complains of a weak urinary stream. The second is Samantha, a 55 year old woman who says that she “pees” a little when she laughs. Samantha also has 2 children and both were delivered naturally.
Now, both these individuals seem to have urinary incontinence. Urinary incontinence is a problem where the process of urination happens involuntarily, meaning that a person might urinate without intending to. This is particularly problematic because it affects a person’s personal hygiene as well as their social life in a way that can be very limiting.
Let’s talk about physiology real quick. As urine flows from the kidneys into the bladder, the bladder starts to fill. Lining the bladder is a layer of transitional epithelium containing “umbrella cells”. These cells physically stretch out as the bladder fills, just like an umbrella opening up in slow-motion. This expansion is further aided by the relaxation of the muscular layer within the bladder’s walls, called the detrusor muscle. At some point, the bladder fills up with urine that would eventually exit the body through the urethra. Now, the urethra is wrapped up in some muscles that can prevent urine from leaking out. The first one is the internal sphincter muscle, which is made of smooth muscle and is under involuntary control and typically opens up when the bladder is about half full. The second one is the external sphincter muscle, and it’s made of skeletal muscle and is under voluntary control. This is the reason that it’s possible to stop urine mid-stream by tightening up that muscle. Once urine has passed through the external sphincter muscle, it can no longer be stopped.
Now, when specialized nerves in the bladder wall sense that the bladder is about half full, they send impulses to the spinal cord at levels S2 and S3, known as the micturition center, and the pons of the brain. The spinal cord response is part of the micturition reflex. And it causes an increase in parasympathetic stimulation and decrease in sympathetic stimulation which makes the detrusor muscle contract and the internal sphincter relax. It also decreases motor nerve stimulation to the external sphincter allowing it to relax as well. At this point, urination would occur, if not for the pons. The pons is the region that we train to voluntarily control urination. If we want to delay urination, the pons overrides the micturition reflex, and when we want to urinate, the pons allows for the micturition reflex to happen.
Now, there are several types of urinary incontinence. The first one is stress incontinence where urine leaks out when there’s a high abdominal pressure. Then there’s urgency incontinence where there’s a sudden urge to urinate. Then there’s mixed incontinence, which is a combination of stress and urgency incontinence. Finally, there’s overflow incontinence, when the bladder doesn’t empty completely. Let’s now look at them one by one.
Let’s start with stress incontinence which is due to increased abdominal pressure that overwhelms the sphincter muscles and allows urine to leak out. Some activities like sneezing, coughing or laughing increase abdominal pressure. This increases the pressure in the bladder and in turn, urine leaks out. If the pressure in the bladder is greater than the pressure in the sphincters, then the sphincters are unable to hold urine in. For your tests, remember that if the sphincters are damaged, which is also called an outlet incompetence, then they can’t stop urine from leaking out. Now, outlet incompetence, can be caused by urethral hypermobility or intrinsic sphincter deficiency. Now, urethral hypermobility is a condition where the urethra can’t be kept still by the muscles surrounding it because they are waaay too weak. One thing that can weaken the pelvic muscle is vaginal delivery. On the other hand, intrinsic sphincter deficiency is caused by damage to these sphincter muscles, which is often a complication of prostate surgery. Okay, now, another risk factor for stress incontinence can be obesity, because it increases the abdominal pressure and therefore, pressure in the bladder can sometimes be higher than the pressure of the sphincter. Similarly, pregnancy can also cause stress incontinence since the uterus rests above the bladder. The diagnosis can be made based on a positive bladder stress test where you can directly see urine leaking out when a person’s coughing or does the Valsalva maneuver. This is when the clinician bears down and squeezes the abdominal muscles in order to increase abdominal pressure and cause urine to leak out. Stress incontinence treatments typically focus on strengthening the pelvic floor muscles by doing Kegel exercises. In individuals with obesity, weight loss is recommended. And in females, using pessaries might be helpful.
Next there’s urgency incontinence, which is when someone has a sudden urge to urinate because of an "overactive bladder", followed immediately by involuntary urination. This is typically due to an uninhibited detrusor muscle that contracts randomly. This usually results in frequent urination, especially at night. For your tests, remember that urgency incontinence is usually associated with urinary tract infections. That’s because the inflammation in the bladder might trigger the detrusor muscle, causing it to contract out of nowhere. For diagnosis, urodynamic studies are generally not needed, but if performed, they will show detrusor overactivity. Now for your exam, it’s important to remember that the first line treatment for urgency incontinence relies on Kegel exercises, bladder training, like establishing a timetable for when to go to the bathroom and empty the bladder, as well as distraction or relaxation techniques. If behavioral training fails to improve the symptoms, medications such as antimuscarinics like oxybutynin can be used to decrease detrusor muscle contractions.
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