A Decade after the Tokyo Sarin Attack: A Review of Neurological Follow-Up of the Victims

Military Medicine, Jun 2007 by Hoffman, Azik, Eisenkraft, Arik, Finkelstein, Arseny, Schein, Ophir, Et al

Objective: On March 20, 1995, sarin gas was used in Tokyo by members of the Japanese "Uhm-Shinrikiu" cult, killing 12 and injuring >5,500 innocent people. Most of the casualties were mildly injured. This article reviews the neurological follow-up data for some of the victims over the past decade. Methods: We reviewed the published literature regarding neurological follow-up of the victims, dividing the data according to the time elapsed after the attack. Results: The digit span test, finger-tapping test, and computerized posturography were the only performance tests that showed statistically significant differences between the victims and the control groups in some of the surveys. The main sequela 7 years after the attack was post-traumatic stress disorder. Conclusions: The results emphasize the need for a national preparedness program for such mass casualty events, led by national health systems. This should include long-term, neurological, follow-up monitoring with performance tests and a post-traumatic stress disorder screening test.

Introduction

More than a decade ago, on March 20,1995, the nerve agent sarin was used in a terror attack in Tokyo by members of the Japanese "Uhm-Shinrikiu" cult. Sarin, a potent inhibitor of the enzyme acetylcholinesterase, causes a prompt flux of the neurotransmitter acetylcholine, resulting in a variety of peripheral and central neurological symptoms. The attack took place during the morning rush hour, in several subway stations simultaneously. More than 5,500 civilians, including members of the rescue teams, were injured. Most of them (4,073) suffered only mild symptoms (mainly ocular) and were dismissed from hospital after a few hours; 984 victims suffered moderate injuries, without the need for mechanical ventilation, 50 victims had severe injuries and needed mechanical ventilation and resuscitation, and 12 people died as a result of the attack.1

The international St. Luke's Hospital, which was closest to the scene, received 640 of the casualties, of whom two died shortly after their arrival.2 The Japanese Sendai army hospital reported treating 62 casualties, all of whom were sent home 1 week after the attack with only ocular complaints.3

The Tokyo sarin attack is actually the largest nerve agent exposure of a civilian population to date. Since this terror attack, both governments and health organizations are taking steps to prepare themselves for the possibility of a nonconventional terror attack.4

In this article, we summarize a decade of neurological follow-up for some of the victims of the Tokyo sarin attack. In most of the studies, information was gathered in the early years following the attack, because of increased medical and public interest, as well as relatively accessible data.

Methods

We reviewed the data of the studies published to date on the victims, focusing on neuropsychological performance, memory tests, balance tests, and signs of post-traumatic stress disorder (PTSD). We divided the studies into three subgroups, based on the time that elapsed from the terror attack to the time the study was carried out, i.e., (1) studies carried out up to 1 year after the attack, (2) studies carried out up to 3 years after the attack, and (3) studies carried out >3 years after the terror attack.

Studies Carried Out Up to 1 Year after the Attack

A group of 18 victims was admitted to St. Luke's Hospital after the attack.5 They were discharged after being diagnosed as suffering from mild sarin intoxication. This group underwent neuropsychological follow-up examinations 6 to 8 months after the event. After completion of a questionnaire aimed at diagnosing PTSD, the neurophysiological effects were evaluated by using electroencephalography and event-related potential, visual evoked potential, and brainstem auditory evoked potential monitoring. The patients did not suffer from any other diseases and did not express any signs of organophosphate intoxication at the time the study was conducted.

In another study, questionnaires were sent to victims treated at St. Luke's Hospital 1 month after the attack.6 The questionnaires were PTSD oriented, dealing with fear, avoidance of trains, sleep disorders, and mood changes. Approximately 80% of the victims complied and filled out the questionnaires.

Yokoyama et ai.7,8 conducted balance performance tests, memory tests, and neurobehavioral tests, looking for signs of PTSD in a group of 18 victims suffering from mild organophosphate intoxication. The tests were performed 6 to 8 months after the attack and included computerized posturography, the Wechsler Adult Intelligence Scale, the digit symbol test, the picture completion test, and the digit span test. Computerized tests for neurobehavioral assessment (finger-tapping, stimulation reaction time, and continuous function tests) and selfevaluation questionnaires (general screening, mood profile, and PTSD questionnaires) were also performed.

Studies Carried Out Up to 3 Years after the Attack

Fifty-six matched, control, police and rescue team personnel involved in the rescue efforts had medical follow-up assessments, including neurobehavioral tests, balance test, vibration threshold test, and psychomotor tests, 3 years after the attack.9 The study group was divided into two subgroups, that is, individuals who were treated in an outpatient clinic and probably were exposed to low doses of sarin and individuals who were hospitalized after exposure to high doses of sarin. The latter group was further divided into those who lost consciousness or had signs of hypoxia and those who did not. The information gathered included results of psychomotor performance tests (finger-tapping, simple reaction time, and choice reaction time tests), memory tests (digit span test and Benton visual retention test), balance tests, and questionnaires, including the Impact of Event Scale (IES) questionnaire and a general health questionnaire (GHQ).