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Neuromagnetic Assessment of Pathophysiologic Brain Activity Induced by Minor Head Trauma

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Neuromagnetic Assessment of Pathophysiologic Brain Activity Induced by Minor Head Trauma AJNR Am J Neuroradiol 20:857±866, May 1999 Neuromagnetic Assessment of Pathophysiologic Brain Activity Induced by Minor Head Trauma Jeffrey David Lewine, John T. Davis, John Henry Sloan, P. W. Kodituwakku, and William W. Orrison, Jr BACKGROUND AND PURPOSE: Patients with mild traumatic brain injury (TBI) often show signi®cant neuropsychological dysfunction despite the absence of abnormalities on traditional neuroradiologic examinations or EEG. Our objective was to determine if magnetic source imaging (MSI), using a combination of MR imaging and magnetoencephalography (MEG), is more sensitive than EEG and MR imaging in providing objective evidence of minor brain injury. METHODS: Four subject groups were evaluated with MR, MSI, and EEG. Group A con- sisted of 20 neurologically normal control subjects without histories of head trauma. Group B consisted of 10 subjects with histories of mild head trauma but complete recovery. Group C consisted of 20 subjects with histories of mild head injury and persistent postconcussive symp- toms. The 15 subjects included in group D underwent repeat examinations at an interval of 2 to 4 months. RESULTS: No MR abnormalities were seen in the normal control group or the asymptomatic group, but ®ve (20%) of the patients with persistent postconcussive symptoms had abnormal MR ®ndings. EEG was abnormal for one subject (5%) from the normal control group, one (10%) from the asymptomatic group, and ®ve (20%) from the group with persistent postcon- cussive symptoms. MSI was abnormal for one subject (5%) from the normal control group, one (10%) from the asymptomatic group, and 13 (65%) from the group with persistent po- stconcussive symptoms. There was a direct correlation between symptom resolution and MSI ®ndings for the symptomatic head trauma group. CONCLUSION: MSI indicated brain dysfunction in signi®cantly more patients with postcon- cussive symptoms than either EEG or MR imaging (P , .01). The presence of excessive ab- normal low-frequency magnetic activity provides objective evidence of brain injury in patients with postconcussive syndromes and correlates well with the degree of symptomatic recovery. Patients with mild traumatic brain injury (TBI) of- changes may be identi®ed clinically, but traditional ten show signi®cant neuropsychological dysfunc- neuroimaging studies rarely reveal consistent brain tion despite the absence of any abnormalities on changes to explain these problems (4±6). The sig- traditional neuroradiologic examinations or EEG. It ni®cant structural changes that CT and MR imag- is well established that severe blunt trauma can ing show in cases of severe TBI tend to be absent cause brain atrophy, but the neural consequences of in cases of mild TBI (7±9), and EEG generally relatively minor head injury remain poorly under- shows normal or only mild, diffuse pathophysiol- stood (1±3). Symptoms such as persistent head- ogy, even in patients with very speci®c cognitive aches, nausea, cognitive decline, and personality and psychological de®cits (10, 11). Because the sensitivity of traditional methods to Received September 30, 1998; accepted after revision January trauma-induced brain dysfunction is so low, many 20, 1999. patients with neurologic bases for their post- From the New Mexico Regional Federal Medical Center, Albuquerque (J.D.L., J.T.D., W.W.O.); the Departments of Ra- traumatic psychological de®cits fail to be diag- diology (J.D.L., W.W.O.), Psychology (J.D.L.), Neurology nosed with TBI or are misdiagnosed as psychiatric (W.W.O.), and Psychiatry (P.W.K), the University of New problems (12). As a result, the conditions of many Mexico School of Medicine, Albuquerque (J.D.L., J.T.D., of these patients are not treated or the patients are W.W.O.); and St Joseph's Rehabilitation Center, St Joseph's referred for inappropriate psychotherapy. Especial- Medical Center, Albuquerque (J.H.S.). ly in cases of mild trauma, there is a general re- Address reprint requests to Jeffrey David Lewine, PhD, De- luctance to medically treat speci®c postconcussive partment of Radiology, University of Utah School of Medicine, 1A71 Medical Center, 50 N Medical Dr, Salt Lake City, UT problems, such as attentional de®cits, in the ab- 84132. sence of a clear neurobiological basis for the prob- lem. Clearly, availability of reliable, objective ev- q American Society of Neuroradiology idence that a particular brain region has been 857 MS 858 LEWINE AJNR: 20, May 1999 rendered dysfunctional by mild TBI would aug- a history of mild head trauma who had achieved ment patient care by allowing clinicians to better complete recovery. Group C consisted of subjects develop cost-effective, individually tailored treat- with postconcussive symptoms subsequent to mild ment and therapy programs (13). head trauma. The subjects included in group D Considering the above, the need to develop neu- were a subset of control subjects and symptomatic roimaging techniques responsive to mild TBI is all patients who underwent repeat examinations. too apparent. Magnetic source imaging (MSI) of- fers promise because it provides a high degree of resolution of normal and abnormal brain physiol- ogy in both spatial and temporal domains (14±19). Methods MSI involves the integration of anatomic data ob- The study population consisted of four subject groups. tained by the familiar method of MR imaging with Group A was composed of 20 healthy volunteers (age range, electrophysiological data obtained by magnetoen- 18±57 years; 10 men and 10 women) with no history of closed cephalography (MEG). Electrical currents ¯owing head injury or other neurologic or psychiatric problems. These within dendrites give rise to extracellular current volunteers were studied as a normal control population. sources and sinks, which establish the scalp poten- Group B consisted of 10 subjects (age range, 14±60 years; tial gradients measured by EEG. These currents six male and four female subjects) with a history of mild closed head injury with brief loss of consciousness (,20 min- also give rise to a surrounding neuromagnetic ®eld utes). At the time of the neuroimaging evaluation (2±16 that is measured by MEG. The biophysics of EEG months after the initial trauma), no postconcussive symptoms and MEG are complementary. MEG provides a se- were present, as indicated by self-report, mini-mental status lective re¯ection of activity in dendrites oriented screening, clinical evaluation, and a symptom questionnaire parallel to the skull surface, whereas EEG re¯ects modi®ed from the Structured Clinical Interview DSM-IIIR mostly activity arising in dendrites perpendicular to nonpatient version interview schedule. All the subjects in the skull. It is noteworthy that electrical conductiv- group B were free of diagnosed neurologic or psychiatric dys- function. All had Glasgow Coma Scale scores of 131 at the ity differences between the brain, CSF, skull, and time of initial hospital admission, and all were discharged scalp smear and distort the scalp-EEG view of the within 24 hours. brain's electrical activity but have minimal impact Group C consisted of 20 subjects (age range, 17±62 years; on MEG (14±19). In many instances, MEG data 12 male and eight female subjects) with a history of mild can be evaluated using straightforward mathemat- closed head injury with brief loss of consciousness (,20 min- ical models that allow localization of the neuronal utes). In all cases, trauma was blunt and associated with a generators of particular signal components. motor vehicle accident, a blow to the head, or a fall. The re- sults of the CT study were interpreted as normal for all patients Normal MEG data, like normal EEG data, are except two, one of whom had right frontal and parietal sub- dominated by frequencies above 8 Hz. Severe TBI dural hematomas and one of whom had a right temporal tip usually causes a shift in the background EEG pow- contusion. (Additional information regarding these patients, er spectra toward lower-frequency signals, but sim- subjects 3 and 6, respectively, is provided in Table 1.) At the ilar changes are rarely apparent in cases of minor time of neuroimaging evaluation (2±38 months after the initial TBI (10). Several investigators have observed that trauma), signi®cant postconcussive symptoms were present, as MEG more often reveals low-frequency signals indicated by self-report, mini-mental status screening, and a symptom questionnaire modi®ed from the Structured Clinical than does simultaneously conducted EEG (16, 20). Interview DSM-IIIR interview schedule. All the subjects in We therefore hypothesized that MEG might reveal group C were free of premorbid diagnosed neurologic or psy- trauma-induced changes in the spectral content of chiatric dysfunction. All had Glasgow Coma Scale scores of spontaneous brain activity, even in cases of rela- 131 at the time of initial hospital admission, and all were tively minor trauma. MEG studies of patients with discharged within 24 hours. Sixteen subjects showed some de- stroke and of patients with tumors frequently reveal gree of cognitive dysfunction (memory or attentional prob- the presence of abnormal low-frequency magnetic lems), two reported only pain (frequent headaches and body activity (ALFMA) with a dipolar magnetic ®eld aches) as a persistent symptom, and two reported pain and depression without cognitive changes. con®guration. Source modeling of ALFMA shows Group D consisted of 15 subjects (10 from the normal con- that individual dipolar slow-wave events are gen- trol group and ®ve from the symptomatic head trauma group) erated by compromised tissues at the margins of who underwent complete follow-up examinations during a 2- lesions (15, 16, 21±23). In patients with epilepsy, to 4-month interval after the initial study. An attempt was MSI reveals that sources of focal ALFMA co-lo- made to follow up all the subjects, but only 50% of the control calize with sources of spikes, even when there is subjects and 25% of the trauma subjects were available.
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