DISCUSSION

The results of this study indicate that electrically injured patients performed more poorly on select neuropsychological measures of attentional interference, mental processing speed, current Full Scale IQ, and motor skills when compared to a well-matched control group of healthy electricians. These findings could not be attributed to demographic differences since the groups were well matched for premorbid IQ level, age, educational level, and occupational background; in addition, those EI patients who sustained traumatic brain injuries because of EI-related falls were excluded from the study, thus the current findings are not the result of traumatic brain injury to the patient group. Likewise, factors such as preinjury psychiatric history, current distress level or upper extremity motor impairment could not statistically account for group differences in attention and mental processing speed. Moreover, all EI patients sustained their injury from peripheral electrical contact only. Only one member of our EI sample reported any preinjury history of psychiatric difficulties or treatment, and our measure of current distress (i.e., BDI) was independent of neuropsychological functioning. Additionally, despite the high rate of litigation involvement inherent in our population because of the work-related nature of many of these injuries, EI patients in litigation did not significantly differ in their performance in any of the measured cognitive domains or expression of depressive symptoms, and all EI patients passed measures designed to detect suboptimal test-taking effort. It is important to note that by design the EI patients included in our sample had sustained no direct mechanical contact of the power source to the head, no traumatic brain injury due to secondary falls, and only one patient in our sample suffered cardiac complications suggestive of possible anoxic injury (all potential causes of cognitive impairment themselves). Thus, the findings of this study indicating poorer attention and mental processing speed appear to reflect direct neuropsychological effects on the central nervous system caused by the electrical exposure itself.

Findings of neuropsychological difficulties in attention and mental speed closely mirror the symptom complaints commonly reported in electrically injured patients (Primeau et al., 1995; Pliskin et al., 1998). In one series, 49% of EI survivors reported difficulties with concentration, 46% reported problems thinking quickly, and 44% reported memory problems (Pliskin et al., 1998). Self-reported memory complaints often reflect problems with attention/concentration rather than anterograde memory dysfunction per se. It has been our experience that many of our EI patients do not complain that they are unable to pay attention or concentrate but rather that it is less automatic and requires greater effort to do so. Considering the occupational status of many of the patients in our sample, these impairments in attention and mental speed can pose challenges in the workplace where attention to detail and exertion of mental effort are critical for maintaining safe workplace practices.

It is possible that the deficits in attention and mental speed observed in our EI sample are interference-related effects secondary to the pain syndromes commonly experienced by electrically injured patients (Kim & Bryant, 2001). Indeed, many of our patients had complaints of chronic pain due to peripheral nervous system injuries, headaches, parasthesias, and lingering effects of burns (Pliskin et al., 1998), and chronic pain from multiple sources aside from electrical injury has been linked to decrements in neuropsychological test performance (McCracken & Iverson, 2001). Future studies of EI will need to employ chronic pain comparison groups (without CNS injuries) to clarify the relationship between neuropsychological test performance and chronic pain following EI.

As noted previously, electrical injury is associated with a high psychiatric morbidity, although most studies reporting neuropsychological deficits following EI did not control for the presence of mood disturbance in their samples. We utilized the BDI as a measure of general distress in our study. Although robust group differences in depressive symptoms were observed, covariation for depressive symptoms had no effect on group differences in cognitive performance, indicating no significant relationship between depressive symptoms and our outcome measures. It is possible that neuropsychological changes and psychological distress are coexisting but unrelated sequelae of EI, with distress being a common manifestation of any traumatic experience, but not significantly contributing to neuropsychological dysfunction. Yet, considering that none of the patients in our sample reported any preinjury psychiatric history, the emergence of new psychiatric difficulties in EI, particularly PTSD (Mancusi-Ungaro et al., 1986), could reflect changes to central nervous system (CNS) function. Future studies of electrical injury will need to consider the possible impact of PTSD on neuropsychological function.

Group differences in attention and mental speed observed in this study could not be attributed to premorbid intellectual level, psychiatric history, litigation status, depression, suboptimal test-taking effort, or demographic factors. Thus, the current data point to genuine CNS changes as a result of electrical injury. Yet, the pathophysiology underlying these impairments remains unclear. Demonstrable structural lesions are rare in this population following peripheral contact injuries, although there are isolated case reports of lesions detected on magnetic resonance imaging (MRI) following peripheral contact injuries (Sahiner et al., 2002). We hypothesize that neuropsychological and neuropsychiatric changes in EI relate to electrochemical alterations in brain systems. By way of comparison, electroconvulsive therapy (ECT) has been studied extensively and we speculate that ECT may serve as a model for understanding the impact of more extreme field strength exposure suffered by electrical injury patients.

ECT involves CNS exposure to a relatively small electrical field and produces positive alterations in emotional status and transient disruption of cognitive function with no overt evidence of structural damage to the CNS. Moreover, efficacy of psychiatric benefit is maximized when the current used is double that necessary to induce a seizure (Chanpattana et al., 2000). Behaviorally, neuropsychological dysfunction is prominent following ECT and primarily includes confusion, disorientation, and retrograde and anterograde memory disturbance (Sackeim, 1994; Rosen et al., 2003). Like electrical injury, prospective investigations of the effects of ECT on brain morphology using MRI have yielded negative findings (e.g., Coffey et al., 1988, 1991). These findings have led investigators to conclude that changes in neuropsychiatric and neuropsychological status following ECT result from electrochemical changes at a neuronal functional level rather than structural changes (Rami-Gonzales et al., 2003). Though the exact mechanisms mediating the therapeutic effect of ECT are currently unknown, several hypotheses have been offered including current-induced changes in cell membranes (i.e., electroporation; Johansson, 1987), up-regulation of serotonergic systems, reduction in dopamine autoreceptors which results in increase in dopamine release from nerve terminals (Ishihara & Sasa, 1999), and attenuation of GABA systems which is associated with a rise in seizure threshold (Fink, 2001). Based on the current findings, one may reason that a similar, but more severe pathophysiology is characteristic of electrical injury. That is, in EI, where field strength exposure far exceeds that administered during ECT, similar but more severe and long-lasting neurochemical alterations are likely to produce stable, nontransient neuropsychiatric and neuropsychological dysfunction in the absence of detectable structural lesions.

Finally, it is important to note that our findings may not be representative of the injury experience of all victims of EI. Our sample was comprised of mostly self-selected patients who have required medical intervention and/or exhibited long-term dysfunction. It remains unclear whether individuals who experience less severe injuries would demonstrate similar dysfunctions of attention, mental speed, and motor deficits as those who sought out the Chicago Electrical Trauma Research Program because of persistent cognitive and emotional complaints. Thus, our convenience sample may not reflect the broader experience of others sustaining electrical injury. Additionally, some cognitive domains were computed using variables from multiple measures whereas others were computed from multiple variables from a single measure. The extent to which method variance may have contributed to the findings is unclear and these findings need to be replicated. Finally, the relatively small number of participants in the study presents a potential limitation in power, meaning that the influence of litigation status or other potential confounds cannot be completely ruled out. Clearly, future research utilizing larger sample sizes is needed.

In sum, this study indicates that cognitive changes do occur in patients suffering from electrical injury. Previous studies have shown that EI victims who sustain a direct mechanical contact from the power source to the head, or those who sustain traumatic brain injuries secondary to falls or anoxia suffer from neuropsychological impairment (e.g., Grube & Heimbach, 1992; Duff & McCaffrey, 2001). However, to our knowledge, this is the first investigation to demonstrate the presence of cognitive impairment in the form of attention and mental speed deficits for EI patients who have sustained an electrical injury specifically through a peripheral point of contact (i.e., the extremities). Further research, especially longitudinal studies that follow EI survivors from the point of injury into the future will be most informative in clarifying what has been a challenging area for clinical neuroscientists and mental health providers.