Differentials
Distal renal tubular acidosis
SIGNS / SYMPTOMS
Rarely symptomatic, but patients may have a history of renal calculi or nephrocalcinosis.
INVESTIGATIONS
Urine pH ≥6.3 on urinalysis with normal anion gap metabolic acidosis is indicative of distal renal tubular acidosis (dRTA). However, dRTA can occur in medullary sponge kidney .
Serum bicarbonate is the most sensitive and specific test for most forms of RTA. The finding of low serum bicarbonate concentration is the usual starting point for investigating metabolic acidosis.
Renal papillary necrosis
SIGNS / SYMPTOMS
Nocturia, polyuria; haematuria, flank pain, pyelonephritis. Rarely renal dysfunction.
INVESTIGATIONS
Passage of sloughed tissue in urine.
Increased serum creatinine reflecting chronic kidney disease may be seen.
Low specific gravity on urinalysis or low urine osmolality during water deprivation.
Tuberculosis of kidney
SIGNS / SYMPTOMS
History of tuberculosis.
History of both upper and lower tract collecting system involvement.
INVESTIGATIONS
Positive urine mycobacterial culture, positive tuberculosis skin test.
Intravenous urography shows calyceal blunting, papillary necrosis ureteral strictures, and bladder, vas deferens, seminal vesicle, or prostate calcifications.
Polycystic kidney disease
SIGNS / SYMPTOMS
Patients may have hypertension, which is not classically seen with medullary sponge kidney (MSK).
Progressive chronic kidney disease may be present, whereas this is extremely rare for MSK.
INVESTIGATIONS
Polycystin 1 or 2 gene mutation.
Cortical cysts seen on CT or ultrasound.
Urea and creatinine may be elevated.
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