The Myths of Mild Traumatic Brain Injury: the 15% number

One of the most popular myths perpetuated by the media and some in the scientific community is that 15% of patients who have suffered a mild traumatic brain injury (MTBI) do not recover by one year and may even experience permanent symptoms. An important point that I try to teach people is to always obtain the original article that is cited in support of such claims so that the validity of the claim can be examined. In this case, the reference often cited is a 1995 study by neurologist, Michael Alexander. In his paper, he wrote the following: "At one year after injury approximately 15% of MTBI patients have not recovered’’ (p. 1256).

When researchers cite Alexander's study as the only reference for this figure, it casts the impression that he is the person who collected the data to support it. However, if one reads Alexander's paper, it is seen that Alexander based his 15% figure on two earlier studies: McLean and colleagues (1983) and Rutherford and colleagues (1979). To begin with, McLean and colleagues only followed 20 patients for one month not one year. In addition, his study consisted of 11 patients with MTBI, 8 patients with moderate TBI, and one patient with a severe TBI. One can hardly use a study of all severity TBI patients at one month post-injury to argue for the chronic effects of MTBI.

The main source of the myth, however, comes from Alexander's summary of the Rutherford article. Rutherford followed 131 MTBI patients for a year and he did indeed find that 19 (14.5%) complained of symptoms at that point. A detailed analysis of Rutherford's patients, however, reveals some interesting details. First, there were actually 145 patients in the study and of these, only 131 followed up. Assuming the missing 14 did not have symptoms one year post-injury, that changes the number to 13.1%. Of the 19 patients who were still reporting symptoms at one year, 8 were involved in lawsuits and 6 (5 of whom were in lawsuits) were suspected of malingering six weeks post injury. Malingering was defined in this study by: bizarre and exaggerated descriptions of symptoms and strange responses during routine examination. Can we really trust the self-report of symptoms in these individuals to be reliable and valid? The answer should be obvious.

In addition to the numbers above, 10 of 19 patients reported one new symptom at one year post-injury that was NOT reported at six weeks post-injury. If the symptoms were brain injury based, they should not appear at one year post injury when not present at six weeks post-injury. More information is that 6 of the 19 patients had only ONE symptom at one year and 7 of 19 patients had two symptoms at one year. This is not enough to classify patients with what is sometimes referred to as "post concussion syndrome" which is traditionally described in the literature as the presence of three or more symptoms at three months post injury. In the end, we are left with 6 subjects who endorsed between 4 and 9 symptoms. And when we take 6 and divide it by 131 we get 4.5%. If we use the entire sample of 145 patients, the number drops to 4%. This is consistent with the estimate (<5%) provided by Iverson in his 2005 review of MTBI. In sum, by simply checking the original sources, one can easily see than the 15% estimate is a truly a myth.

REFERENCES

Alexander, M. P. (1995). Mild traumatic brain injury: Pathophysiology, natural history and clinical management. Neurology, 45, 1253–1260.

Greiffenstein, M.F. (2008). Clinical Myths of Forensic Neuropsychology. The Clinical Neuropsychologist, 10, 1-11.

Iverson, G. L. (2005). Outcome from mild traumatic brain injury. Current Opinion in Psychiatry, 18, 301–317.

McCrea, M. (2007). Mild traumatic brain injury and postconcussion syndrome. The new evidence base for diagnosis and treatment. New York: Oxford University Press.

McLean, A., Temkin, N. R., Dikmen, S., & Wyler, A. R. (1983). The behavioral sequelae of head injury. Journal of Clinical Neuropsychology, 5, 361–376.

Rutherford, W. H., Merrett, J. D., & McDonald, J. R. (1979). Symptoms at one year following concussion from minor head injuries. Injury, 10, 225–230.