abnormal EEG on left side of brain

My son is 5yrs old and has a metabolic disorder called Tyrosinaemia Type 1. This genetic disease means he is on a low protein diet. His teachers suspected blank episodes/peti mal so he had an EEG and a sleep depried EEG wich showed abnormal spikes on the left side of the brain both times.
What does this mean? He is booked for MRI in about 2months but I need to understand what this may mean. What possibilities could there be? Is it linked to his high protein levels? Does this indicate a brain tumor? Could he be prone to seizures? He has never had a seizure before or "blanked". I suspect he was tired because at that time he had a few restless nights. Please help me I am soo worried.