VA Morning Report 2.12.18: Urinary obstruction– not all BPH

Case summary: Thanks to Scott “Red bone” Goldberg for presenting the fascinating case of an 85M with PMH well-controlled HIV, who presented requesting additional home services and was found to be in acute renal failure from obstructive uropathy.

Top pearls:

  1. The differential diagnosis for bilateral hydronephrosis is: lower urinary tract obstruction (bladder, urethra) OR bilateral upper urinary tract obstruction (bilateral ureters or kidneys).
  2. Renal ultrasound in AKI to evaluate for obstruction is most useful in: 1) older patients, 2) those with a history of obstruction, 3) those with a history of intra-abdominal malignancy.
  3. FeNa and FeUrea were validated in oliguric patients (e.g. UOP <500cc/day), so use caution interpreting results in the non-oliguric setting.
  4. The main clinical presentations of tenofovir nephrotoxicity are (a) proximal tubular dysfunction with preserved renal function and (b) proximal tubular dysfunction associated with decreased renal function. Decreased renal function may be classified as AKI, CKD, or a glomerular filtration rate (GFR) that is decreased when compared with baseline values, albeit within normal limits.

Sites of urinary obstruction

  • Manoj brought up a great question: Are there any non-obstructive causes of hydronephrosis?
    • Massive diuresis can cause mild hydronephrosis on imaging that is not clinically obstructive
    • Pregnancy can also cause hydronephrosis on imaging that is not clinically obstructive
  • Pearls on signs/symptoms:
    • Spontaneous urination does NOT rule out obstruction, as tubular injury can impair urinary concentration and urethral obstruction can lead to bladder distention and overflow incontinence, both of which can cause polyuria.
    • Hydronephrosis is almost always asymptomatic, and pain should prompt a consideration of additional diagnoses such as stones, papillary necrosis, or infection.
  • Is all obstruction BPH?! Can seem like it at the VA, but obstruction can occur anywhere along the urinary tract.
    • Remember that foley placement will not relieve obstruction of the upper urinary tract (proximal to the bladder)!
      • Even if foley placement produces a gush of urine or reduction in PVR, renal impairment and hydronephrosis will persist.
      • This typically requires either ureteral stent or nephrostomy tube depending on the site of obstruction.
    • Bilateral hydronephrosis Ddx:
      • lower urinary tract obstruction (bladder, urethra)
      • OR bilateral upper urinary tract obstruction (bilateral ureteral or kidney)
    • Age can be an epidemiologic clue:
      • kids- anatomic abnormalities (including urethral valves or stricture and stenosis at the ureterovesical or ureteropelvic junction) account for the majority of cases in children.
      • young adults- calculi
      • older adults- prostatic hypertrophy or carcinoma, retroperitoneal or pelvic neoplasms, and calculi
    • Recovery:
      • Prognosis depends on severity and duration of obstruction.
        • With total ureteral obstruction, for example, there is evidence that relatively complete recovery of glomerular filtration rate (GFR) can be achieved if obstruction is relieved within one week, while little or no recovery occurs after 12 weeks
      • If recovery occurs, it is dramatic and rapid, with a return to baseline renal function within 7-10 days (and often even more quickly).

Screenshot 2018-02-12 at 10.14.52 AM - Edited

Tenofovir and renal injury

  • TDF is a prodrug of tenofovir that can cause AKI, proximal tubular dysfunction, or both in combination.

    • Proximal tubular dysfunction=Fanconi’s syndrome=hypophosphatemia, renal glucosuria (glucosuria with a normal serum glucose concentration), hypouricemia, and/or aminoaciduria
    • Side note: Sjogren’s, MM and a host of other systemic diseases can also cause Fanconi’s!
  • TDF is also associated with increased risk of chronic kidney disease in large observational studies

  • Risk of renal injury overall ranges from 2-10%.
  • TDF should be avoided, if: 1) GFR<60 at baseline, 2) >25% decline to GFR<60 after starting

  • TAF (a new prodrug) was approved in 2015 based on studies showing significantly smaller decline in eGFR and similar reductions in VL.
  • The VA’s own Mike Schlipak (Chief of General Medicine and creator of cystatin-C!) published much of the seminal work on tenofovir and renal injury.

Reference: Scherzer R, Estrella M, Li Y, Choi AI, Deeks SGGrunfeld CShlipak MG. Association of tenofovir exposure with kidney disease risk in HIV infection. AIDS. 2012 Apr 24; 26(7):867-75.


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