Republican presidential candidate Donald Trump launched a scathing attack on his most significant rival, retired neurosurgeon Ben Carson, telling an audience in Iowa that Carson described himself as pathological in his memoir. To a rather muted assembly of supporters with placards, Donald Trump typically didnt hold back.

Carsons an enigma. He wrote a book, and hes doing great in Iowa. Hes second in the polls. With all these professional politicians, Im first, Carsons second, and I dont understand it, I really dont understand it. Because he wrote a book and in the book he said terrible things about himself. He said that hes pathological and that hes got basically pathological disease, said Trump.

In his autobiography, Gifted Hands, Carson describes himself as a troubled youth with a temper that led him to attack several of his friends and even his mother, before he turned his life around. Trump compared people who are pathological to paedophiles.

If youre pathological, theres no cure for that folks. OK? Theres no cure for that. And I did one of the shows today, and I dont want to say what I said but Ill tell you anyway. I said that if youre a child molester, a sick puppy, youre a child molester, theres no cure for that. Theres only one cure − we dont want to talk about that cure. Thats the ultimate cure. No, theres two, theres death and the other thing, he said.

Trump also questioned the veracity of an incident from his Carsons youth in which he claimed that he attempted to stab a friend, but that his knife broke on this friends belt buckle.

Then heres the beauty of all, he took a knife and he went after a friend and he lunged, he lunged that knife into the stomach of his friend, but low and behold it hit the belt, it hit the belt, and the knife broke. Give me a break, give me a break, give me a break, he said.

Carson has bristled at news media attempts to confirm the stabbing incident and other accounts in his autobiography, saying he is being unfairly targeted.