Post-Traumatic Stress Disorder (PTSD) is a psychiatric disorder in which symptoms such as re-experience, hyperarousal, and avoidance follow an experience of unpredicted traumatic stress.¹ PTSD does not present identically for all who experience the same type of trauma because the development of the disorder is influenced by the individual's vulnerability factors.² PTSD vulnerability factors include trauma inflicted during childhood, personality disorders, genetic vulnerability to psychiatric disorders, and recent drastic change in the living environment, among others.³ Those who have these susceptibilities may develop PTSD after a relatively small mental trauma.⁴

Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by lack of attention, impulsiveness, and hyperactivity⁵ and is a developmental disorder that affects 50% of child and adolescent psychiatric outpatients. ADHD is a common neurodevelopmental disorder associated with family and social problems, behavioral and educational difficulties, and cognitive dysfunction.⁶ In the past, ADHD was considered a childhood disorder because the symptoms were thought to improve as the child develops.⁷ However, 50-65% of ADHD patients continue to satisfy the diagnostic criteria after they reach adulthood. Adults with ADHD have a prevalence ratio of 3-5%,⁸ and studies have consequently concluded that ADHD symptoms need to be treated well into adulthood.⁹ ADHD that emerges during childhood may be accompanied by antisocial personality disorders, anxiety disorders, and depressive disorders,⁹ and a number of studies report that mood and depressive disorders are comorbid.^10,11 Among depressive disorders, the symptoms of PTSD can appear similar to those of ADHD, necessitating differential diagnosis.^12,13 Also, the symptoms of ADHD are often perceived as personality or character traits of the individual and are thus overlooked.¹⁴ Because of comorbidities and other factors, the symptoms of ADHD in adults are easily overlooked, difficult to evaluate, and often ignored.¹⁴

In South Korea, most soldiers are in late adolescence when they begin military service. Late adolescence is a developmental phase involving the transition to adulthood, and late adolescents do not yet have a fully developed or effective stress response system.¹⁵ Enlisting in the military entails many environmental changes and continuous tension, and many of these youths experience considerable psychological pressures in military life.¹⁶ Serious maladjustment to military life can engender many societal problems.¹⁷ Military service begins with basic military training, which introduces stressors such as the unfamiliar environment of the training center and the individual's new role as a soldier.¹⁸ It has been reported that stress is most severe during the basic military training period and in situations of compulsory military service such as in Israel.¹⁹ Individuals with ADHD symptoms have difficulties adjusting to new environments as well as low self-efficacy.²⁰ Considering these factors, it can be assumed that individuals with ADHD symptoms may have a hard time adjusting to the military environment, and the variety of environmental stressors could induce the development of PTSD. However, the literature regarding adult ADHD in Korea is meager at present. Past studies on adjustment to military life have focused primarily on environmental factors, and there is still a strong need for research on the psychopathology of this adjustment. Moreover, most studies on ADHD and PTSD have been retrospective or focused on children. This study aims to comprehend the effects of past and present symptoms of adult ADHD on the stress and symptoms of PTSD. The subjects of this study were new recruits participating in the 5-week long basic military training in South Korea.

Two hundred and fifty-eight participants answered the first survey, and 271 participants answered the second survey. Only the 224 participants who answered both the first and second surveys were included as study subjects. The first survey was conducted on the first day after admittance, and the second survey was conducted after the 5 weeks of basic military training.

The demographic variables are shown in Table 1. The mean age of the 224 new recruits participating in the study was 19.8±1.1, and college enrollment (92.4%) was the most common education level. The results revealed that 1.3% had a personal medical history of psychiatric disorder, and 2.7% had a family medical history of psychiatric disorder. The changes in the stress scale and IES-R-K scores before and after the training are shown in Table 2. A significant decrease in the stress scale was observed after the 5-week long training. The BEPSI-K score was 1.51±0.4 before training and 1.26±0.5 after the 5-week training (p<0.01). The PTSD symptoms represented by the IES-R-K score also displayed a significant decrease after training (p<0.01); the test yielded a score of 10.2±11.7 before training and 3.8±5.5 after the five-week training. The group presenting questionable PTSD (IES-R-K score over 18 points) consisted of 44 subjects (19.6%) before training and 4 subjects (1.8%) after training.

The correlations among the presence and absence of the ADHD symptoms in the past and in the present, the IES-R-K score, and the BEPSI-K score were analyzed (Table 3). Before training, the coefficients of correlation between the IES-R-K score and the K-WURS score and between the IES-R-K score and the K-AADHDS score were 0.575 and 0.642, respectively, which indicates significant correlation (p<0.01). After five weeks of training, the coefficients of correlation between the IES-R-K score and the K-WURS score and between the IES-R-K score and the K-AADHDS score were 0.213 and 0.172, respectively, which indicates significant correlation (p<0.01). In the first week of training, the coefficients of correlation between the BEPSI-K score and the K-WURS score and between the BEPSI-K score and the K-AADHDS score were 0.606 and 0.524, respectively, indicating significant correlation (p<0.01). After the five-week training, the coefficients of correlation between the BEPSI-K score and the K-WURS score and between the BEPSI-K score and the K-AADHDS score were 0.248 and 0.161, respectively, which indicates significant correlation (p<0.05 and p<0.01, respectively). The PTSD risk factors before and after training are shown in Table 4. In the first week of training, all of the past and present ADHD symptoms were risk factors for the PTSD questionable group (IES-R-K≥18). The risk of PTSD in the group that exhibited present ADHD symptoms was 1.145 times higher. The risk of PTSD in the group that showed past ADHD symptoms was 1.049 times higher than in the group without past ADHD symptoms. The risk of PTSD in last week was 1.073 times higher in the group with PTSD symptoms in first week than in the group without PTSD symptoms in first week (Table 5). Path analyses of the past and present ADHD symptoms and the PTSD symptoms before and after training were conducted to examine any causal relationships (Figure 1). The model was validated with a chi-squared of 8.934 and a significance level of p=0.112. The GFI was 0.985, which exceeds 0.9 and thus indicates high validity, and an AGDF of 0.956 also confirmed the validity of the model. Other indexes of model validation were as follows: RMSEA=0.059, RMR=0.709, and CFI=0.988.

Regarding the effects of the exogenous variables on the endogenous variables found in the path analysis, the path coefficient from the K-WURS score, which represented past ADHD symptoms, to the K-AADHDS score, which represented present ADHD symptoms, was 0.40 (S.E: 0.024, C.R: 16.918), and that to the first week IES-R-K score, which represented the PTSD symptoms before training, was 0.21 (S.E: 0.073, C.R: 2.878); both coefficients indicate direct effects. Regarding the path coefficients between the endogenous variables, the path coefficient from the K-AADHDS score to the first week IES-R-K score, was 0.86 (S.E: 0.137, C.R: 6.26), indicating direct effects. The path coefficient from the first week IES-R-K score to the last week IES-R-K score, which represented the PTSD symptoms after training, was 0.17 (S.E: 0.03, C.R: 5.672), indicating direct effects. All of the abovementioned path coefficients were significant at the 5% level.

This study was a 5-week long prospective study conducted to investigate the effects of ADHD symptoms on PTSD symptoms using new recruits participating in basic military training as the study subjects. The group with past and present adult ADHD symptoms had a higher risk of developing PTSD symptoms than the group without symptoms. In addition, a causal relationship between ADHD symptoms and PTSD symptoms was found. The IES-R-K and BEPSI-K scores decreased significantly after training. This result is similar to those of past studies that also used new recruits as the subjects. It seems that improved understanding about and adjustment to military life as well as the establishment of new relationships in a community setting led to psychological stability as the training progressed.²⁷ Also, the relief of safely completing the challenging physical training likely reduced depression and anxiety.^28,29

The new recruits who had experienced ADHD symptoms during childhood or the preceding 6 months had a higher risk of exhibiting PTSD symptoms before the training. The new recruits who had experienced PTSD symptoms before the training were also more likely to exhibit PTSD symptoms after the training. These results indicate that past and present ADHD symptoms are risk factors for PTSD symptoms, which is similar to the results of past studies.^2,12 One study reported that PTSD patients had activity levels as high as those of ADHD patients when compared with the normal control group; that study concluded that comorbidity of these two diseases is possible and differential diagnosis is important.³⁰ Another study comparing a panic disorder patient group and a PTSD patient group showed that the PTSD group exhibited more past and present ADHD symptoms than the panic disorder group and reported that ADHD is a PTSD vulnerability factor.² Yet another study reported that, when exposed to traumatic stress, ADHD patients and ODD patients exhibited stronger PTSD symptoms than adjustment disorder patients.¹² These results, like those of this current study, suggest that ADHD symptoms can heighten the risk of PTSD.

However, a study that comparatively analyzed an ADHD patient group and a normal control group reported that, although the risk of developing PTSD after exposure to trauma is not related to ADHD, mania is a risk factor for PTSD.³¹ The symptoms of ADHD and mania are difficult to differentiate, and it is easy to overlook the ADHD symptoms when both are present.³² Because this study completely precluded those subjects who were found to have major psychiatric disorders like mania in the post-conscription physical examination, it was impossible to compare mania and ADHD in this study.

A deficiency in executive function is characteristic³³ of adults exhibiting ADHD. A study conducted on Vietnam War veterans found that low executive function was a risk factor for PTSD.³⁴ A PTSD study conducted in Korea on the survivors of gun murder cases in the military also reported that executive function deficiency was a risk factor for PTSD.³⁵ A twin study also indicated that executive function deficiency was a risk factor of PTSD.³⁶ Considering the numerous past studies that suggest executive function deficiency is present in ADHD and PTSD, the deduction that ADHD and PTSD are closely related to executive function deficiency was made from the path analysis results of this study.

This study has several limitations. First, the evaluating instruments used in this study were not able to diagnose ADHD or PTSD. Subjects were included in the study when ADHD or PTSD was questionable or when symptoms were present, which cannot be taken as clear diagnoses. Second, a differential diagnosis is needed because ADHD and PTSD share many symptoms.³⁷ For example, symptoms such as attention difficulties, fidgeting, impulsiveness, annoyance, and others may simultaneously exist in these two disorders.³⁸ This study did not attempt to differentiate these two disorders, which might have affected the results. Therefore, a study in which a diagnosis and a differential diagnosis are made by a proficient interviewer is needed. Third, several studies assert that ADHD has many comorbidities.^11,39-41 The comorbidities influence ADHD in a number of ways when present, but this study was not able to exclude these comorbidities. However, the new recruits were examined to confirm the absence of major diseases in the mental and physical health examinations before they entered military service. For this reason, it was considered unlikely that the new recruits had comorbidities.

Despite these limitations, this prospective study of adult ADHD symptoms and PTSD symptoms is significant. Furthermore, because the study subjects belonged to the same community, confounding factors such as type of trauma, degree of exposure, sex, age, etc. were relatively controlled. By examining ADHD symptoms in soldiers and observing the progress of PTSD symptoms, this study is expected to aid in the evaluation and understanding of the social issues underlying soldier adjustment. Based on the results of this study regarding the relationship of symptoms between PTSD and ADHD, it will be possible to study the biological etiology shared by ADHD and PTSD.