nephrocalcinosis

Nephrocalcinosis is the deposition of calcium salts in the kidney parenchyma, most often in the renal medulla and papillae. It is distinct from nephrolithiasis, though stones may coexist. The finding is usually detected by imaging and may be incidental or associated with kidney dysfunction.

Causes include conditions that raise calcium or phosphate concentrations in urine or renal tissue. Common contributors are distal renal tubular acidosis, hypercalciuria, hypercalcemia, hyperparathyroidism, and hyperoxaluria (including primary hyperoxaluria). Chronic kidney disease, certain systemic illnesses, and medications or treatments with a high phosphate load or aggressive calcium/ phosphate imbalance can also lead to nephrocalcinosis. Medullary sponge kidney is a recognized associated condition.

Pathophysiology involves precipitation of calcium phosphate or calcium oxalate crystals in the renal interstitium and tubules when solute concentrations exceed solubility. In distal RTA, urine is alkaline, favoring calcium phosphate deposition. Recurrent injury or impaired nephron function can promote ongoing calcification.

Clinical features range from asymptomatic to symptoms related to impaired kidney function. Some individuals experience flank pain, hematuria, urinary tract infections, or a progressive decline in renal function if calcification is extensive.

Diagnosis relies on imaging and laboratory data. Ultrasound may show increased echogenicity of the renal pyramids; noncontrast CT is more sensitive for calcifications. Lab tests can reveal metabolic abnormalities such as hypercalciuria, hypercalcemia, hyperphosphatemia, or metabolic acidosis, depending on the underlying cause.

Management focuses on treating the underlying disorder and preserving kidney function. Strategies include hydration, correction of metabolic abnormalities (for example, bicarbonate for distal RTA), reducing calcium excretion (thiazide diuretics in hypercalciuria), and managing hyperphosphatemia. Prognosis depends on extent and the treated underlying condition, with risk of progression to chronic kidney disease if unaddressed.