This happens because our kidney’s concentrating ability is limited. For every liter of ocean water that we drink, an additional 1/2 liter of freshwater is needed to excrete the total salt load consumed. Rodents’ kidneys have more than 2 times the concentrating ability of humans’, hence they can survive on salty sea water.
Common causes: Stone, infection and tumor (MRS SIT)a
Patients with BPH have increased risk of urinary tract infection. In this case, a patient with longstanding hx of voiding symptoms, now presents with acute irritative symptoms due to development of cystitis or prostatitis.
Risk factors for extension: uncontrolled diabetes, immunosuppression, urinary stones, urinary tract abnormalities, presence of indwelling structures (e.g., Foley catheter, urinary stent), pregnancy, etc.
1 In sexually active patients with prostatitis <35 years of age, or >35 years of age with high risk sexual behavior, MCC are gonorrhea and chlamydia. For these patients, test for STD and initiate empiric treatment that covers these organisms.
Presentation: history of pyelonephritis with no clinical improvement despite adequate treatment, with persistent flank pain and high-grade fever. Exam may reveal palpable abdominal mass. UA may reveal pyuria, but urine culture may be negative (when abscess is not communicating with urinary system).
aPatients can also present with recurrent UTIs or recurrent bacteriuria of the same organism. Treatment is similar to acute bacterial prostatitis: use fluoroquinolone (ciprofloxacin or levofloxacin) or trimethoprim-sulfamethoxazole for total of 6 weeks.
bProstate may be mildly tender. Treatment includes a trial of empiric antibiotic therapy (e.g. ciprofloxacin) and alpha-1 blocker (e.g., tamsulosin). In sexually active males, rule out STD prostatitis and consider infection with atypical organism (chlamydia, mycoplasma, etc.). In patients with hematuria, do further urologic workup (including cystoscopy).
cIn patients with chronic irritative bladder symptoms of unknown cause, particularly in patients > 40 years of age, or in patients with persistent hematuria we must rule out urogenital cancer by doing cystoscopy and urine cytology.
Presentation: Older male patients presenting with chronic voiding symptoms. Patient may also have chronic mild urgency and frequency. Benign prostatic hyperplasia (BPH) alone usually does not cause dysuria.
Exam: Digital rectal examination may reveal firm, smooth enlargement of prostate gland; however, there is a poor correlation between prostate enlargement (by exam or transrectal US) and obstructive symptoms due to BPH. Workup: NSIDx is urinalysis, serum creatinine, and prostate-specific antigen (PSA) to screen for prostate cancer.
Drug of choice is alpha-1 antagonist which act on smooth muscles. Tamsulosin is preferred, because it has fewer side effects than other drugs in this group. Prazosin and doxazosin (+ azosin) can be considered when patients have coexistent hypertension
If patient continues to have symptoms, NSIM: add a 5-alpha reductase inhibitor (inhibits conversion of testosterone to dihydrotestosterone). They act on the epithelial portion of prostate, and has been shown to reduce prostatic volume. For example, finasteride and dutasteride (+terides)
Transurethral resection of prostate is indicated, if symptoms do not improve significantly with medical management or patients develop complications (e.g., hydronephrosis, renal failure, recurrent infection.)
Presentation: In most patients, prostate cancer is suspected when found to have high PSA levels or abnormal digital rectal examination. Symptoms, when present, are often due to metastatic disease, such as low back pain/bone pain or pathological fracture (especially around the lumbar vertebra region).
Either prostate tissue ablation with radiation or removal with surgery + androgen depriving therapyd
dProstate cancer is an androgen-dependent cancer, so decreasing androgen production will shrink the tumor. This can be achieved by either removing both testicles (surgical orchiectomy) or by using medical therapy to decrease androgen production (as shown below).
GnRH agonist: leuprolide, goserelin,a nafarelin, etc. (+ relins)
Mechanism of action: Continuous stimulation by GnRH paradoxically results in downregulation of androgen production
Risk factors: Phenacetin-containing analgesics, pioglitazone (possible), ethanol, smoking, Schistosoma haematobium (parasitic infection), aniline dyes, arsenic exposure, cyclophosphamide (chemotherapy).
NSIM is UA (best initial test): symptomatic stones usually present with hematuria. Alkaline pH (pH > 7.5) may signal possible infection with urease-producing bacteria (e.g., Proteus, Klebsiella) and possibility of staghorn calculi. Urine pH < 5.5 may suggest uric acid stone.
It has high sensitivity and specificity. In pregnant patients, do renal ultrasound, as CT scan is not desirable.
5 Do not use contrast when looking for stones (or hemorrhage). Stones, blood, and contrast have similar high density appearance on CT. Using contrast will muddle the picture. For example, first diagnostic test in suspected stroke is CT scan of head without contrast. On the other hand, when looking for malignancy or infection use IV contrast. For example, first diagnostic test in a patient with fever and a new focal neurological deficit is CT scan of head with contrast.
Always check stone composition after its removal or spontaneous passage, because it determines preventive strategies
A 25-year-old female presents with urinary frequency, urgency, dysuria, and hesitancy for the last few days. Exam reveals suprapubic pain and mucopurulent discharge out of urethra. She has hx of multiple sexual partners. UA is leukocyte esterase positive but nitrites negative.
A 42-year-old male presents with few weeks hx of urinary frequency, urgency, dysuria, and dribbling of urine. For the last few days he also started noticing painful, tender, and swollen testes. Exam reveals tender testes and prostate.
7. A 67-year-old male has few years hx of intermittent bloody urine, urinary frequency, urgency, dysuria, and dribbling of urine. He has no hx of fevers, chills, but has had significant unintentional weight loss. UA shows multiple RBCs and only few WBCs. What is the likely Dx?
A 50-year-old male presents with few months hx of bloody urine, urinary frequency, urgency, dysuria, difficulty urination, and dribbling of urine. He has no hx of fevers, chills or weight loss. UA shows multiple RBCs and only few WBCs. Prostate exam is unremarkable.
Best initial test: serum creatinine and blood urea nitrogen (BUN). Creatinine is the most sensitive indicator of renal failure and is used to calculate glomerular filtration rate (GFR). The following properties make creatinine one of the best indicators of renal function:
bBladder outlet obstruction is a common reason for acute renal failure in old patients. Causes include urethral stricture, prostate cancer, benign prostatic hypertrophy, cervical cancer, retroperitoneal fibrosis, stone in bladder-neck, atonic bladder, etc.
cFractional excretion of sodium (FENa). In addition to serum sodium and creatinine, we need urine sodium and urine creatinine to calculate this ratio, but no need to remember the formula of FENa as it will be given in exam. A hypoperfused kidney will try to conserve Na by increasing reabsorption of Na+.
7 Caution: Do not rely on FENa when patients are on diuretics or have preexisting tubular disease. In patients on diuresis, use FEUrea instead. Urea is also an osmolyte like Na, but it is not affected by diuretics.