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Metabolic disorder

Author: Pediatric Oncall

Question
A 6 years old girl born of third degree consanguineous marriage presented with repeated episodes of vomiting followed by altered sensorium and drowsiness. There was no fever or jaundice. She had normal milestones and was immunized till date. On examination, she was comatose with Glasgow coma scale of 7, had hypertonia with brisk deep tendon reflexes and extensor planters with bradycardia and hypertension. There was no focal neurological deficit and pupils were bilaterally equal reacting to light. Other systems were normal. Her raised intracranial tension responded to mannitol. Investigations showed serum ammonia of 178 mg/dl and MRI brain showed hyperintense foci in the cerebral white matter near lateral ventricular margins with minute quantity of lactate peaks in MR spectroscopy. Her serum lactate: pyruvate ratio was 103. Muscle biopsy showed normal mitochondria in muscle. Urine organic acids showed increased uracil and orotate suggestive of urea cycle defects. She was treated with IV sodium benzoate and carnitine to which she responded. She continued to have asymptomatic hyperammonemia over next 3 years and has normal scholastic performance. Her repeat ammonia was 102 mg/dl at 9 years of age and lactate and pyruvate were normal. She was continued on sodium benzoate.

What is diagnosis? Why did the child have high lactate: pyruvate ratio initially?

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