**Question:** A 2 year old boy presents with fever for 3 days which responded to administration of paracetamol, Three days later he developed acute renal failure, marled acidosis and encephalopathy. His urine showed *nt of oxalate crystals. The blood anion gap and osmolal gap were increased. Which of the following is the most likely diagnosis -

A. Urosepsis
B. Cystinuria
C. Hyperoxaluria
D. Hypokalemic periodic paralysis

**Core Concept:**

Hyperoxaluria is a condition characterized by elevated oxalate levels in the body. Oxalate is a normal constituent of the human diet, but when its excretion exceeds its production, it can lead to the formation of oxalate crystals in various tissues, causing multiple organ involvement.

**Why the Correct Answer is C - Hyperoxaluria:**

In this case, the patient presented with fever initially, which responded to paracetamol. However, subsequent symptoms like acute renal failure, marble-like acidosis, and encephalopathy occurred, pointing towards a kidney-related issue. The presence of oxalate crystals in urine is a key clue for the diagnosis of hyperoxaluria.

**Why Other Options are Incorrect:**

A) Urosepsis (pyelonephritis) typically presents with acute renal failure, but not the marked oxalate crystals and elevated anion gap.
B) Cystinuria is another condition causing crystalluria, but it is characterized by cystine crystals, not oxalate crystals.
D) Hypokalemic periodic paralysis is a neuromuscular disorder, unrelated to renal oxalate crystals and acidosis.

**Clinical Pearl:**

Hyperoxaluria should be considered in children presenting with renal failure and oxalate crystals in urine, as this condition can lead to multiple organ involvement and potentially severe complications. Early diagnosis and intervention are crucial to prevent further deterioration of the patient's condition.