GOUT & THE KIDNEY in Objective-C

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The kidney is the primary organ for excretion of uric acid Patients with proximal tubular dysfunction have decreased excretion of uric acid and are more prone to gouty attacks Depending on the pH and uric acid concentration, deposition can occur in the tubules, the interstitium, or the urinary tract The more alkaline pH of the interstitium causes urate salt deposition, whereas the acidic environment of the tubules and urinary tract causes uric acid crystal deposition at high concentrations Three disorders are commonly seen: (1) uric acid nephrolithiasis, (2) acute uric acid nephropathy, and (3) chronic urate nephropathy Renal dysfunction with uric acid nephrolithiasis stems from obstructive nephropathy Acute uric acid nephropathy presents similarly to acute tubulointerstitial nephritis with direct toxicity from uric acid crystals Chronic urate nephropathy is caused by deposition of urate crystals in the alkaline medium of the interstitium; this can lead to fibrosis and atrophy Treatment between gouty attacks involves avoidance of food and drugs causing hyperuricemia, aggressive hydration, and pharmacotherapy aimed at reducing serum uric acid levels These disorders are seen in both overproducers and underexcretors of uric acid The latter situation may seem counterintuitive; however, these patients have hyperacidic urine, which explains the deposition of relatively insoluble uric acid crystals

Kramer HJ et al The association between gout and nephrolithiasis in men: The Health Professionals Follow-Up Study Kidney Int 2003 Sep;64(3):1022 6 [PMID: 12911552]

Renal dysfunction associated with sickle cell disease is most commonly due to sickling of red blood cells in the renal medulla because of low oxygen tension and hypertonicity Congestion and stasis lead to hemorrhage, interstitial inflammation, and papillary infarcts Clinically, hematuria is common Damage to renal capillaries also leads to diminished concentrating ability Isosthenuria (urine osmolality equal to that of serum) is routine, and patients can easily become dehydrated Papillary necrosis occurs as well These abnormalities are commonly encountered in sickle cell trait Sickle cell glomerulopathy is less common but will inexorably progress to ESRD Its primary clinical manifestation is

Other diseases with variable involvement described elsewhere in this chapter include systemic lupus erythematosus, diabetes mellitus, and the vasculitides such as Wegener s granulomatosis and Goodpasture s disease

Specific information regarding imaging studies, renal biopsy, and aging issues involving the kidney appears in CMDT Online at http://wwwaccessmedicinecom

If gross hematuria occurs, a description of the timing (initial, terminal, total) may provide a clue to the localization of disease Associated symptoms (ie, renal colic, irritative voiding symptoms, constitutional symptoms) should be investigated Drug ingestion and associated medical problems may also provide diagnostic clues Anticoagulants, analgesic abuse (papillary necrosis), cyclophosphamide (chemical cystitis), antibiotics (interstitial nephritis), diabetes mellitus, sickle cell trait or disease (papillary necrosis), a history of stone disease, or malignancy should all be investigated The presence of hematuria in patients receiving anticoagulation therapy warrants a complete evaluation consisting of upper tract imaging, cystoscopy, and urine cytology Physical examination should emphasize signs of systemic disease (fever, rash, lymphadenopathy, abdominal or pelvic masses) as well as signs of medical renal disease (hypertension, volume overload) Urologic evaluation may demonstrate an enlarged prostate, flank mass, or urethral disease Initial laboratory investigations include a urinalysis and urine culture Proteinuria and casts suggest renal origin Irritative voiding symptoms, bacteriuria, and a positive urine culture in the female suggest urinary tract infection, but follow-up urinalysis is important after treatment to ensure resolution of the hematuria Further evaluation includes urinary cytology, upper tract imaging, and cystoscopy Cytology assists in the diagnosis of bladder neoplasm Upper tract imaging (usually abdominal and pelvic CT scanning without and with contrast) may identify neoplasms of the kidney or ureter as well as identifying benign conditions such as urolithiasis, obstructive uropathy, papillary necrosis, medullary sponge kidney, or polycystic kidney disease CT urography and MRI have replaced intravenous urography (IVU) when imaging the upper tracts for sources of hematuria The role of ultrasonographic evaluation of the urinary tract for hematuria is unclear Although it may provide adequate information for the kidney, its sensitivity in detecting ureteral disease is lower In addition, its higher degree of operator dependence may further confound the issue Cystoscopy can be used to assess for bladder or urethral neoplasm, benign prostatic enlargement, and radiation or chemical cystitis For gross hematuria, cystoscopy is ideally performed while