Solution: The patient has obvious medullary nephrocalcinosis on CT. The differential is broad, but includes three primary and most common etiologies; medullary sponge kidney, hyperparathyroidism, and renal tubular acidosis (Type 1, distal). RTA can be primary (hereditary), or secondary to a systemic process as in this case. Autoimmune disorders including Sjögren's syndrome and Lupus are relatively common underlying etiologies. The symptoms and findings can be reversed with treatment. As an aside, some believe that the character "Tiny Tim" in the Christmas Carol had Type 1 RTA. This would explain his symptoms and response to therapy.