What is the most likely diagnosis?
This case is classical depiction of medullary sponge kidney, with dilated renal tubules and multiple tiny calcifications within the tubules (seen in excretory phase).
What is the differential of medullary nephrocalcinosis?
Differential includes: hyperparathyroidism; medullary sponge kidney; renal tubular acidosis (type 1); hypervitaminosis D; milk-alkali syndrome; other pathological hypercalcemic or hypercalciuric states (e.g. Cushing syndrome; multiple myeloma).
What biochemical investigations may be of benefit in assessing patients with medullary nephrocalcinosis?
Calcium metabolism related markers would be useful: serum calcium, phosphate, bicarbonate, alkaline phosphatase etc.. as well as parathyroid hormone levels.
What is the approximate incidence of medullary sponge kidney?
It is common, seen in 1 in 5000 individuals.
Does the condition explain the chronic back-ache patient is having?
Medullary sponge kidney is usually asymptomatic, but may present with urinary tract infection (UTI), haematuria or urolithiasis / ureteric colic. In this patient degenerative changes in spine may account for the chronic backache.
CT IVP demonstrates numerous small calcifications located in the renal calculi which are non-obstructing and measure up to 3mm on the right and 4mm on the left. Urographic phase imaging demonstrates dilated renal tubules in which these non-obstructing calculi are located.