The Subjects consisted of 903 males (age 40.7 ± 16.6) and 1,416 females (age 41.1 ± 18.5) who visited for the first time the Department of Psychosomatics Medicine at Toho University Omori Medical Center in the period from February 2007 to July 2008. First, subjects were examined by interview doctors to confirm that they had the 13 symptoms used in the diagnosis criteria of panic attack in DSM-IV. Second, psychosomatic medicine specialists excluded physical diseases such as arrhythmia, angina, hyperthyroidism, chronic obstructive pulmonary disease (COPD), asthma, pheochromocytoma, and neurological disorders, including evident epilepsy. Subjects were informed of the medical significance [22
] of EEG for all patients diagnosed with panic disorder. Finally, 115 subjects between the ages of 18-65 who gave consent to EEG check were selected. The list was further shortened to 70 subjects (20 males, age 33.2 ± 8.2 and 50 females, age 35.0 ± 9.5) when the following groups were excluded:
1) Patients who regularly take psychotropic drugs and other medicines with EEG effects 2) Patients with schizophrenia, severe depression, and personality disorders
3) Patients with alcoholism or drug abuse
4) Patients with severe complications of circulatory, respiratory, digestive, endocrine and neurological disease.
The selected 70 subjects were made aware of the purpose and methods of the study. They were assured that study data would be anonymously and statistically treated. It was also made clear that personal data would not be disclosed to anyone including administrative authority. Questions from subjects were readily answered and subjects were given the choice to decline to participate in the study without fearing any consequences.
The Ethics Committee of Faculty of Medicine Toho University approved this study. They also approved EEG check of panic disorder patients within normal medical examination procedures. Furthermore, to avoid delay in the commencement of treatment, EEG technicians were advised to check patients EEG on the first examination day.
For EEG record, Nihon Kohden EEG-1514 leads were attached to both earlobes (A1 and A2). The reference electrode was 12 channels: Fp1, Fp2, C3, C4, P3, P4, 01, 02, F7, F8, T3 and T4, according to the international 10-20 system of Electrode Placement, and the EEG was recorded for 15 consecutive minutes or more. The bipolar leads were 12 channels: Fp1-F3, Fp2-F4, F3-C3, F4-C4, C3-P3, C4-P4, P3-01, P4-02, Fp1-F7, Fp2-F8, F7-T3 and F8-T4, and the EEG was recorded for 2 consecutive minutes or more. Photic stimulation was given at 10 second intervals at 3, 5, 6, 8, 10, 12, 14, 15, 18, 20 and 24 Hz, and hyperventilation was carried out for 5 minutes at 3 second intervals. The time constant was 0.3 seconds by high cut filter 120 Hz and the contact resistance was 10 kΩ or less.
[EEG record reading and interpretation]
EEG record reading was based on the decision criteria of adult EEG proposed by Teruo Ohkuma in 1999, which are widely accepted in Japan. The criteria details are 1) EEG with eyes closed is composed of α wave or faster activity than α wave. Obvious θ and δ waves do not appear. 2) α waves and fast activity show normal localization. 3) There is no difference of 20-30% or more in the amplitude of symmetric parts. 4) There is no difference of 10% or more in the duration of symmetric parts. 5) α attenuation occurs with open eyes, sensory stimuli, and mental activities et cetera. 6) Neither α wave nor fast activity show abnormally high amplitude. 7) No intermittent activities appear, such as spike waves or sharp waves(intermittent abnormal activity, epileptic pattern.
We used the criteria and the author read all EEG records of patients before contact with them. The peculiar EEG patterns which are difficult to read or with clinical significance unknown at present (not taken as abnormal findings in reading EEG), such as 14 & 6 Hz positive spike, small sharp spikes, 6 Hz spike and slow waves, psychomotor variant, SREDA (subclinical rhythmic electroencephalographic discharge of adults) and Wicket spikes were considered normal as long as they were not frequent and their basic activity's localization, rhythmicity and consecutiveness were stable [24
]. The interpretation of the EEGs was finalized after double-checking by my executive doctor.
Logistic regression analysis was performed with EEG findings as dependent variables and with or without the 13 symptoms above, age and sex were independent variables.
We confirmed there was no significant difference with agoraphobia, psychiatric disorders, drinker, and smoker or not (Table ). The independent variables were selected stepwise and by forward selection under the likelihood ratio testing was selected. The SPSS version 13 was used for statistical analysis.
Characteristics of patients with panic disorder subclassified on the basis of EEG findings