Lactic acidosis. This child has presented with an acute episode of encephalopathy. Common causes of encephalopathy include infections {encephalitis}, substance or drug abuse, lead poisoning, metabolic disorders, demyelination and space occupying lesions. Of these, substance abuse, demyelinating disorders and metabolic disorders present with recurrent episodes. Encephalitis usually may be acute or lead to an insidious chronic presentation. It will not present with recurrent episodes with interspersed normal episodes in between similarly space occupying lesions may present with seizures or signs of raised intracranial tension and rarely cause no deterioration over a period of time.
This child has presented with recurrent episodes of disorientation, vomiting and limpness. Her pupils are normal. In case of substance abuse, pupils are one of the clinical markers that give a suspicion of drug abuse. The pupillary reflex is maintained in case of metabolic causes of coma.
Atropine causes fixed, dilated pupils`
Morphine results in small pupils which react normally to light and barbiturates give rise to fixed pupils. Meiosis is seen with organophosphates, opiates and phenothiazines whereas mydriasis is seen with antihistamines, tricyclic antidepressants, alcohol and cocaine. Also with no other evidence of autonomic involvement, substance abuse seems unlikely. Lead poisoning presents with encephalopathy which is not an intermittent variety.
Thus, one needs to consider demyelinating disorders or metabolic disorders in this child. Demyelinating disorders usually cause focal neurological deficits as they predominantly involve white matters. This child has altered behavior which is suggestive of grey matter involvement in addition to hypertonia and brisk reflexes suggestive of white matter involvement. Thus, the most likely cause of encephalopathy in this child is a metabolic cause.
This child’s blood
Glucose was normal. Her urine ketones were negative. She had metabolic acidosis with increased anion gap. Her serum ammonia was marginally elevated {178 µg, dl {Normal : 30 to 90 µg, dl}} and her lactate was 33 mg, dl with pyruvate of 0.32 mg, dl and lactate: pyruvate ratio of 103. MRI brain showed hyperintense signals in cerebral white matter and dorsal aspect of pons suggestive of mitochondrial or organic acidemia. Her urine for toxic screen was negative and muscle biopsy showed irregular muscle fibres. Her urine organic acids and aminoacidogram was normal. Thus she was diagnosed as Lactic Acidosis with recurrent encephalopathy.
E-published: July 2010 Vol 7 Issue 7 Art No. 42