Keratinized squamous metaplasia of the upper urinary tract resulting in recurrent renal colic

A 60-year-old female with an extensive history of stone disease and shock wave lithotripsy presents with recurrent and increasingly severe renal colic. Work-up reveals obstruction with translucent debris that is found to be composed of keratin. Her history of chronic irritation of the collecting system has resulted in keratinizing squamous metaplasia (KSM) with hyperkeratosis that has sloughed from the upper urinary tract and has become lodged in the ureter. Because of the worsening of her symptoms on conservative management, the patient elected for a nephrectomy and her symptoms have since resolved. KSM of the renal pelvis is a relatively rare phenomenon and most often presents with irritative symptoms. It is thought to result from chronic irritation of the urothelium. KSM has been found to be coincident with squamous cell cancers of the urinary tract, though clear data implicating KSM as a premalignant lesion is lacking. We present a case of recurrent renal colic secondary to sloughing keratin debris from KSM.