Traumatic Brain Injury or Intellectual Disability

by Dr. Bradbury

Question: Dr. Bradbury, I read your columns regularly and a couple of times you have written about diagnosing someone with mental retardation, or intellectual disability. If someone experiences a head injury, and the results of testing are in the intellectually deficient range, how do you decide if the diagnosis is a traumatic brain injury or mental retardation?

That is a great question, and a very interesting question for a psychologist to answer when it is the referral question. If the individual under 18 years of age obtains a Full Scale IQ of 70 or less, and has deficits or impairments in adaptive functioning two or more standard deviations below the mean in two or more areas, a diagnosis of Intellectual Disability (formerly Mental Retardation) can be given, regardless of the cause. A psychologist must always be an investigator. It is extremely important that all records available are obtained and reviewed.

Let’s suppose a 21-year-old male is referred for a psychological evaluation following a closed head injury. Also, let’s suppose that an IQ test is administered and the Full Scale IQ obtained is less than 70. If I were doing the evaluation, I would probably administer an achievement test along with an IQ test. Let’s also suppose the scores obtained on the achievement test are consistent with the IQ test, and that an adaptive behavior scale completed by someone who knows the patient well produces similar results.

With these three pieces of information, one might conclude that the head injury has significantly impaired the functioning of the individual being evaluated. However, to come to that conclusion without considering history would be an improper use of obtained psychological testing data.

I would not give any opinion until educational, medical, and mental health records were obtained and reviewed. Since our patient is only 21 years of age, it is likely that testing data would still be available in the Special Education office of the school district attended if he had been in Special Education. If school records indicated that the patient was an average or above average student and that he had never been referred for Special Education services, there would be an increased likelihood the current subaverage scores are the result of the head injury.

On the other hand, if it is found that the patient was in Special Education and there are a series of psychological evaluations throughout his school years that are consistent with the current testing, one might conclude that his current functioning is unrelated to the head injury and is an intellectual disability.

If the patient were older, it is unlikely that Special Education records would be available because it is required that school districts destroy Special Education records after a period of time (5-7 years). If that were the case, the psychologist must investigate medical records, mental health records, and any standardized testing available on the individual. If it were found that the patient obtained scores in reading and other subjects at the first percentile, that might suggest that the patient was functioning at the current level prior to the head injury. Sometimes, information can be found in medical and mental health records. Evidence of meningitis, FASD, or hypoxia might suggest brain damage at a time prior to the head injury, and the current subaverage scores are probably unrelated to the reported head injury. As you might conclude, the review of records is often much more time consuming that the testing itself.

There is one more thing that must be considered. Head injuries are often associated with litigation and the psychologist must rule out the possibility of malingering for purpose of monetary gain.

Lorin L. Bradbury, Ph.D. is a licensed psychologist in private practice in Bethel. For appointments, he can be reached at 543-3266. If you have questions that you would like Dr. Bradbury to answer in the Delta Discovery, please send them to The Delta Discovery, P.O. Box 1028, Bethel, AK 99559, or e-mail them to