Citation

Merritt VC, Clark AL, Crocker LD, Sorg SF, Werhane ML, Bondi MW, Schiehser DM, Delano-Wood L. Neuropsychologia 2018; 119: 340-348.

Affiliation

Staff Neuropsychologist, VASDHS; Center of Excellence for Stress and Mental Health; Associate Professor of Psychiatry, UCSD, School of Medicine, Department of Psychiatry. Electronic address: ldelano@ucsd.edu.

Copyright

(Copyright © 2018, Elsevier Publishing)

DOI

10.1016/j.neuropsychologia.2018.08.026

PMID

30176300

Abstract

Although across-test intra-individual variability (IIV), or dispersion, has been shown to be a valuable marker of neurological health in a variety of clinical samples, IIV has not been well examined in the context of mild traumatic brain injury (mTBI). In the present study, we examined measures of IIV in military Veterans with and without a history of mTBI. Secondly, we examined how measures of IIV relate to traditional indices of mean cognitive performance, TBI characteristics, and neuropsychiatric symptoms in mTBI. Participants included 120 Veterans (67 mTBI, 53 military controls [MCs]) who completed a comprehensive neuropsychological assessment. Two dispersion indices were calculated using 13 norm-referenced variables: an average standard deviation (ASD) score and a maximum discrepancy (MD) score. Compared to MCs, Veterans with a history of mTBI demonstrated greater IIV as indicated by the MD index after adjusting for relevant demographic variables, PTSD symptoms, and mean-level cognitive performance (p=.027; η_p²=.043), and there was a trend finding in the same direction for the ASD index (p=.091; η_p²=.025). Among the mTBI participants, the two IIV indices were positively correlated with each other (p<.001, r=.921) and negatively correlated with mean cognitive performance (p=.017-.022, r=-[.279-.291]). In contrast, ASD and MD scores were not associated with a measure of premorbid intellectual functioning or neuropsychiatric symptoms (all p's>.05). However, higher ASD scores were positively related to lifetime number of mTBIs, such that greater cognitive variability was observed in Veterans with a history of multiple mTBIs (i.e., ≥3 mTBIs; p=.037, r=.255). Overall, our results demonstrate that Veterans with mTBI show greater IIV relative to MCs, and that repetitive mTBI is associated with increased cognitive performance variability.

FINDINGS indicate that, in the context of mTBI-which is considerably heterogeneous in nature-measures of dispersion may be more appropriate indicators of cognitive dysfunction when compared to traditional mean neuropsychological scores, especially in those with remote mTBI histories. Future longitudinal studies are needed to further establish the long-term clinical implications and brain-based correlates of these findings.

Copyright © 2018. Published by Elsevier Ltd.

Language: en

Keywords

cognitive functioning; dispersion; head injury; intra-individual variability; neuropsychological assessment