This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epilepsy, Subject name: Pharmacology
High plasma drug concentration of phenytoin can cause which of the following adverse effects? 
Select and explain. 
A. Ataxia, B. Hirsutism, C. Gum hyperplasia, D. All of the above
A: Ataxia
Answer: A: Ataxia 
Explanation: Cerebellar dysfunction (ataxia, nystagmus and veigo) is seen at toxic plasma concentrations whereas hirsutism and gum hyperplasia is seen at therapeutic concentrations (but on prolonged use).