Epilepsy is common in autism, with prevalence rates ranging from 7% to 46%, but relatively little is known about the role that the neurologic condition plays in people that have the developmental disorder.

Now researchers from the departments of neurology and neurosurgery at NYU’s Langone School of Medicine think that many patients with autism who experience seizures might have treatment resistant forms of epilepsy.

Study researcher, Orrin Devinsky, MD, and colleagues retrospectively reviewed clinical and laboratory data from 127 patients with idiopathic autism and at least one epileptic seizure who were treated at the NYU Comprehensive Epilepsy Center between 1989 and 2009. Findings were published online first in Epilepsia.

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Treatment resistant epilepsy (TRE) — defined as failure of at least two tolerated, appropriate anti-epilepsy drug regimens — occurred in 33.9% of patients. Another 27.5% of patients did not experience any seizures or auras during a 12-month period and were considered seizure free, and the remaining 38.6% of patients had infrequent seizures and not enough data to be categorized as either TRE or seizure free.

Among the 78 patients in which complete anti-epileptic drug use and seizure control data were available, 42 had TRE (55%). These patients had a trend toward higher rates of motor (54% vs. 35%) and language (72% vs. 65%) delays compared with patients who had infrequent seizures or those who responded to seizure treatment, although the findings were not statistically significant.

Additionally, patients with TRE experienced seizure onset at earlier ages than those who were seizure free (P=0.005).

Among the three patients that underwent surgical resection to control seizures, two experienced limited improvement and one, no improvement. Another nine patients underwent vagus nerve stimulator implantation, seven of which did not experience improvements.

“Our small sample suggests that surgery outcomes in this group are less favorable than in epilepsy populations without autism,” the researches wrote.

Patient enrollment at an epilepsy center may have biased the sample toward a higher frequency of TRE , the researchers noted. They added that selection bias for performing surgical interventions might have also occurred, as many parents did not consider surgery an option because “intermittent partial seizures did not significantly impair quality of life relative to their severe autistic symptoms.”

These findings, along with previous research indicating an association between epilepsy, progressive impairments and increased morbidity in patients with autism, warrant further study, the researchers wrote.

Sansa G. Epilepsia. 2011;DOI:10.1111/j.1528-1167.2011.03069.x.