Even as all these coalescing factors conspire to enhance pain in people with autism, that pain can be extraordinarily difficult to recognize.
In a 2009 study, researchers found that the hearts of children with autism pounded faster while they had their blood drawn than did those of typical children8. But the children with autism made fewer facial expressions, such as grimaces, that indicate pain, perhaps because they have a smaller repertoire of expressive behaviors in general.
“The challenge with autism is that we’re dealing with a population that has altered social behavior,” Moore says. “And pain behavior is a fundamentally social thing.”
Some people with autism may communicate pain in counterintuitive ways. Giesse recalls Matthew’s reaction right after getting his tonsils removed. He threw a tantrum, screaming that he wanted to go home — despite his throat presumably being in significant pain.
Later, Matthew told his mother he had screamed precisely because his throat hurt so much. “But he couldn’t express that to us; for him, it was just to scream,” Giesse says.
Unable to express themselves, some children may turn their frustration outward — or even against themselves.
“A lot of times, pain may be exhibited as an exacerbation of behavioral problems or increased self-injury or aggression,” especially in people with autism who have limited verbal abilities, says Mazurek.
Little research has been done on this topic, but the very behaviors interpreted as a high tolerance to pain — such as head-banging or hand-biting — might be signs that the individual is in agony.
There is some evidence that, at least in some genetic subtypes of autism, there may be a biological basis to pain tolerance. For example, individuals with Phelan-McDermid syndrome, a genetic abnormality often accompanied by autism, are often impervious to aches. Mouse models of this disorder share this feature.
The original 1966 description of Rett syndrome, an autism-linked disorder that affects mainly girls, also alludes to the girls’ ability to withstand great discomfort.
In 2010, the first study to systematically explore pain in Rett syndrome surveyed 646 families in Australia, France and elsewhere, and found that 65 percent of the parents reported that their daughters had a delayed or muted pain response10.
Some girls with Rett laughed instead of crying when they were injured, the parents said. “Often they fractured bones and nobody knew,” says study leader Helen Leonard, an epidemiologist at the University of Western Australia near Perth.
Fractures are a particular problem in girls with Rett syndrome, who tend to have decreased bone density. Families and doctors who care for girls with syndrome “really have to be on the alert for prevention of fractures,” says Leonard. Her team is developing guidelines for protecting and healing the fragile bones of girls with the disorder.
Rett syndrome is caused by a mutation in MeCP2, a gene that governs the expression of many thousands of others. In the past several years, animal studies have shown that MeCP2 helps to orchestrate the perception of pain in the body. Blocking the gene’s action in a rat can suspend the perception of pain after an injury, perhaps explaining the delayed pain responses of girls with the disorder.
MeCP2 has also been implicated in autism, so this mechanism might contribute to altered sensitivity to pain in some individuals with autism as well, Leonard says. But this idea is still speculative.