Incidence of seizures after traumatic brain injury--a 50-year population survey.

BACKGROUND Records of the Rochester Epidemiological Project were used to determine the incidence of secondary seizures after traumatic brain injury (TBI) in all cases treated for this condition in the population of Olmsted County, Minn, from 1935 to 1984. Medical records of the Mayo Clinic and all other medical facilities in Olmsted County, Minn, are in the database of this Project. Incidence rates after TBI were compared with incidence rates of idiopathic epilepsy previously determined for Olmsted County. RESULTS TBI cases were divided into 3 defined severity categories: mild, moderate, and severe. Out of 4541 cases of TBI accumulated in 50 years only 97 cases developed 1 or more seizures (46 cases of seizure secondary to other definite causes were excluded). Incidence rates were highest in the first year after the head injury. The overall excess incidence rate was very low in mild TBI, only 0.3 per 1000 per year, but was higher in severe TBI, with an excess rate of 10 per 1000 per year. Only 7.2% of the TBI cases were classified as severe (loss of consciousness or amnesia for more than 24 hours, subdural hematoma, or brain contusion). CONCLUSION The long-term incidence of seizures beyond the incidence rate of idiopathic epilepsy is low after mild or moderate TBI, but is at the rate of 10 excess cases per 1000 per year in the minority of cases with severe TBI.