THURSDAY, Nov. 15 (HealthDay News) -- In patients with focal epilepsy, simply asking how often they have seizures doesn't provide a true count of their seizure frequency, German research suggests.

Reminding patients to keep written records of their seizures may not help, either, because they may be unaware of some seizures, said the University of Bonn Medical Center researchers.

"In conclusion, patient seizure counts are not valid, and reports of complete seizure freedom may need objective evaluation (e.g., regarding a driver's license)," the study authors concluded.

The study, published in the November issue of the journal Archives of Neurology, included 91 adults with focal epilepsy -- also known as partial seizures -- which involves one specific area of the brain.

The patients were outfitted with electrodes and monitored by video for an average of 4.5 days. They were asked to keep a seizure diary and to push a warning button to summon a nurse when they detected the onset of a seizure.

About half (42) of the patients received daily reminders about documenting all their seizures.

During the study, the patients experienced a total of 582 partial seizures but did not report 323 of them. The researchers found that 85.8 percent of all seizures that occurred during sleep were unreported, compared with 32 percent of seizures that occurred while patients were awake.

"Patients activated the push-button alarm ahead of 51 seizures (8.8 percent) but failed to document 17 (33.3 percent) of these seizures," wrote the study authors, who also found that patient self-reporting varied by seizure type.

Patients failed to report 73.2 percent of complex partial seizures (which impair consciousness) and 26.2 percent of simple partial seizures (which don't affect consciousness).

More information

The Epilepsy Foundation has more about partial seizures.