<prompt> All are true about Trigeminal neuralgia except?If associated with multiple sclerosis MS, often has no trigger spotsIf associated with MS may be difficult to treatMay respond to phenytoinIs more common in patients with causalgia  <response>: 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. 