This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
All are true about Trigeminal neuralgia except? 
Select and explain. 
A. If associated with multiple sclerosis (MS), often has no trigger spots, B. If associated with MS may be difficult to treat, C. May respond to phenytoin, D. Is more common in patients with causalgia
D: Is more common in patients with causalgia
Answer: D: Is more common in patients with causalgia 
Explanation: Ans. D. Is more common in patients with causalgiaTrigeminal neuralgia, whilst usually idiopathic may be secondary to demyelination (in the pons), in which case trigger spots are rare and treatment is often ineffective. Phenytoin, carbamazepine and clonazepam are the usual medical treatments. There is no association with causalgia except the pain mechanism may be similar. Root or root entry zone compression may occur due to tumors or arteries.