2025 – PAGE 385 – NEPHROLOGY

MEDULLARY SPONGE DISEASE

Medullary sponge disease can present with recurrent renal stones and hematuria. Urinalysis is otherwise normal. It’s a congenital disorder of cystic dilations in the collecting system. Besides the morbidity related to the stones, it’s a fairly benign condition.

MNEMONIC: Good prognosis = Everyone loves soft and SPONGY things!

AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is a progressive, multisystemic disorder involving cysts and enlargement of the kidney and other organs (liver, spleen, pancreas). Commonly present with hypertension and pain in the flank, back, or abdomen. Diagnose with ultrasound showing at least 2 cysts in 1 kidney, or 1 cyst in each kidney in a patient under the age of 30. Genetic testing is not routinely performed unless the patient is a potential kidney donor.

AUTOSOMAL DOMINANT TUBULOINTERSTITIAL KIDNEY DISEASE (ADTKD)

Low yield. This rare autosomal dominant condition has several subtypes and has been called several different names, including Medullary Cystic Kidney Disease (now phased out). It is a slowly progressive kidney disease. Renal dysfunction appears in the teenage years and progresses to end-stage renal disease over the course of years to decades (highly variable). Hyperuricemia and gout is a component of the disease for certain subtypes. Look for a strong family history of chronic kidney disease (CKD) or gout.

(DOUBLE TAKE) FANCONI SYNDROME

Fanconi syndrome is the overall dysfunction of the proximal renal tubules, resulting in the loss of amino acids, proteins, electrolytes (sodium, potassium, bicarbonate, and phosphorus), and glucose. It has a number of etiologies, but the most common is cystinosis, a hereditary disease in which cystine accumulation damages the tubules. Look for polydipsia, polyuria, failure to thrive (FTT), and a ton of abnormal labs. The loss of bicarb results in a Type II Renal Tubular Acidosis (RTA), and thus a non-gap metabolic acidosis. The loss of phosphorus can present as RICKETS. Diagnose cystinosis by obtaining a leukocyte cystine level.

PEARLS: There are MANY possible diseases and points of confusion with these diseases. In Fanconi Syndrome, there is loss of sodium, and the serum sodium level is low to low-normal. In arginine vasopressin deficiency or resistance, there is a loss of WATER that can result in hypERnatremia if there’s no access to free water. Lastly, between Fanconi Anemia, Fanconi Syndrome, Diamond-Blackfan, and Shwachman-Diamond, there is tremendous room for confusion. Use mnemonics (PBR’s or your own) to keep them all straight!

NAME ALERT: The name alert is for FANCONI ANEMIA!