What is the classic presentation of cystine nephrolithiasis?

Cystine nephrolithiasis is characterized by the formation of kidney stones composed mainly of cystine, an amino acid. The classic presentation of cystine stones typically includes flank pain due to the obstruction they cause in the urinary tract. However, what sets cystine nephrolithiasis apart is a distinctive odor in the urine, often described as smelling like rotten eggs. This is due to the presence of sulfur-containing amino acids and can be a critical clue in diagnosing this condition.

While unilateral flank pain with hematuria and bilateral flank pain with costovertebral angle tenderness can be presentations of other types of nephrolithiasis, they are not specific to cystine stones. Severe abdominal pain with nausea is also a common symptom in many gastrointestinal or urological emergencies, but it lacks the specificity needed to point directly to cystine nephrolithiasis.

The presence of a foul odor in the urine, specifically a rotten egg smell, is a unique and important clinical finding for cystine nephrolithiasis and helps distinguish it from other types of renal stones. This characteristic, alongside the clinical context, is essential for making an accurate diagnosis.