Abstracts

Rationale:
Unique EEG patterns have been associated with certain metabolic encephalopathies. Bursts of Comb like monophasic negative activity at 5-7 Hz in the central and parasagittal regions has been seen in neonatal maple syrup urine disease and propionic acidemia. Its presence in interictal EEG background of vitamin B6 (pyridoxine) dependent epilepsy has not be described. We report an EEG of a newborn that revealed 7 Hz monomorphic negative comb like rhythm (similar to mu rhythm) independently in the left and right temporal region that responded to pyridoxine challenge.
Method:
This is a term girl born at 41weeks of gestation via cesarean section due to macrosomia (birth weight 10lbs2oz) without complication. At day 10 of life, she became irritable and refused feeds. At this time, she was noted to have episodes of head and eye deviation to the right, flexor contractions of the arms, with lip smacking and rhythmic crying lasting ~15 secs. She was brought to the ED for evaluation and was noted to have low bicarb of 7.6MEq/L and lactic acidosis 17.1MEq/L. Exam was normal aside from a distended abdomen. She was intubated, treated with IV fluids, and 20mg/kg phenobarbital bolus. CT scan of the head revealed an arachnoid cyst in the posterior fossa. Long term video EEG was started which revealed discontinuity and at times burst suppression pattern. There were frequent bursts of medium amplitude ( ~100 uv) monomorphic, arciform, 7 Hz monophasic theta activity in a comb like rhythm lasting 3-4 seconds up to 10 seconds independently in the left and right temporal regions. Despite continued treatment with phenobarbital, the patient subsequently developed electroconvulsive status epilepticus. Levetiracetam was administered and an additional phenobarbital bolus was given; though, electroclinical seizures persisted. Pyridoxine challenge was given (100mg IV bolus) resulting in immediate and dramatic clinical improvement as well as EEG improvement. No further seizure activity was noted. Her EEG subsequently became more continuous. The patient began feeding well and was discharged on vitamin B6 supplementation at a dose of 25mg/kg/d. Keppra and phenobarbital were discontinued.  
Results:
At 5weeks follow up, comprehensive epilepsy genetic evaluation (Invitae) revealed and confirmed pathogenic heterozygous mutation in the ALDH7A1 gene (c246+1G >A).
Conclusion:
Comb like rhythm has been noted in different metabolic epileptic encephalopathy like neonatal maple syrup urine disease, propionic acidemias. However, we noted this in patient with vitamin B6 responsive epilepsy which was genetically proven. Therefore, we believe that presence of this comb like rhythm is not specific for any particular metabolic encephalopathy and diagnostic evaluation with vitamin B6 supplementation should be tried along with other metabolic & genetic screening evaluation.
Funding:
:There was no funding received in support of this abstract.