Chronic Low Back Pain Masking Medullary Nephrocalcinosis Diagnosed by Point-of-Care Ultrasound.

Low back pain (LBP) is a major cause of disability worldwide and is usually attributed to musculoskeletal etiologies. However, non-musculoskeletal causes should be considered in patients with persistent or atypical symptoms. Renal causes, such as renal calcific disorders, are less frequently considered, especially in the absence of urinary symptoms. Medullary nephrocalcinosis is a rare renal calcific disorder characterized by calcium deposition in the renal medullary parenchyma and tubules. We report the case of a 46-year-old woman with a three-year history of chronic LBP without urinary tract symptoms, managed conservatively as musculoskeletal pain, without improvement. Bedside point-of-care ultrasound (POCUS) revealed bilateral echogenic medullary pyramids suggestive of medullary nephrocalcinosis. Confirmatory imaging with computed tomography showed calcification of the medullary pyramids and multiple bilateral renal medullary cysts, consistent with medullary nephrocalcinosis and medullary sponge kidney. This case highlights an atypical presentation of medullary nephrocalcinosis and underscores the diagnostic utility of POCUS as a valuable, low-cost, noninvasive tool for assessing renal causes of LBP.