Self-injury and externalizing pathology: a systematic literature review

Below, the different terms and their presence in the reviewed publications are displayed. It is important to clarify that in general the term ‘self-injurious behaviours’ is used for describing all of these acts, which are not the same as the specific term ‘self-injurious behaviour (SIB)’.

In 7 papers there was no clear distinction between the purpose of the investigated self-injurious act (whether it was with suicidal intent or not) [11‐17], but in the remaining 28 papers the defined self-injurious behaviour was a nonsuicidal act [18‐45].

There were 11 different terms for self-injurious behaviour in the investigated 35 papers.

‘NSSI’ was the most common term: this expression was presented in 10 studies [27, 28, 34‐36, 39‐41, 43, 45]. In accordance with the term itself this expression was used only in nonsuicidal meaning. Six studies used only this term for describing the behaviour [27, 35, 36, 39, 43, 45]. In other studies, NSSI could be found as a part of wider self-injurious behaviours: Jacobson et al. [34] use ‘deliberate self-harm’ (DSH), Nock et al. [40] use ‘self-injurious behaviour’ (SIB), Preyde et al. [41] and Guendelman et al. [28] use ‘self-harm’ for describing both suicidal and nonsuicidal self-injurious behaviours. Darke and Torok [22] used ‘non-suicidal self-harm’ as a term, but their definition was similar to other NSSI definitions.

‘DSH’ was presented in 6 publications [15, 20, 31, 33, 34, 44]. Four studies used it in a nonsuicidal meaning [20, 31, 33, 44], however, 2 studies [15, 34] did not make this distinction. Five papers [15, 20, 31, 33, 44] defined ‘DSH’ as physical self-injurious behaviour, although Jacobson et al. [34] defined it as a possible overdose act as well. Both Aglan et al. [11] and Chou et al. [12] used the term ‘deliberate self-poisoning’ (DSP), which they originated from DSH, but only in the meaning of an overdose, they did not make the suicidal-nonsuicidal distinction.

‘Self-mutilation’ was found in 5 publications [17, 19, 25, 29, 32]. The term is used for nonsuicidal physical self-injurious behaviours, except for Zlotnick et al. [17], who did not distinguish the purpose of the act.

‘SIB’ was a term in 4 papers [37, 38, 40, 42], it is also mainly used in a nonsuicidal meaning, except for Nock et al. [40].

‘Self-injury’ was presented in 4 papers [18, 24, 30, 45], and ‘self-harm’ was found in 3 studies [14, 23, 41]. Young et al. [16] used ‘self-injury’ as a subgroup of ‘critical-incidents’ that they defined as auto or hetero-aggressive acts in an incarcerated population.

There were some other phrases describing self-injurious behaviour: ‘parasuicide’ [13]: there is no distinction between suicidal-nonsuicidal intent; ‘self-inflicted injury’ (SII) [21]: this is a nonsuicidal act; ‘suicide gesture’ [26]: this is a nonsuicidal self-injury or a suicidal attempt to communicate with others.

Among the studies included in our review, diagnostic interviews, self-reported questionnaires and institutional records were used to measure self-injurious behaviours: altogether we found 20 different instruments among the investigated 35 papers.

In 9 cases, the authors designed a longer diagnostic interview, and some questions about self-injurious behaviours were included in it [11, 15, 18, 19, 22, 31, 32, 36, 41].

An interview specially developed for measuring self-injurious behaviours was used in 10 studies [13, 21, 26, 28, 30, 34, 38, 39, 42, 43]. The Self-Injurious Thoughts and Behaviors Interview (SITBI) [46] was applied by Garcia-Nieto et al. [26]. The Lifetime Parasuicide Count (LPC) [47] was used by Jacobson et al. [34], Crowell et al. [13], Crowell et al. [21]. However, in the study of Crowell et al. [21], it was mentioned under a different name: Lifetime-Suicide Attempt Self-Injury (L-SASI). An interviewer-administered modification of the Self-Injurious Questionnaire (SIQ) [48] appeared in the studies of Guendelman et al. [28], Hinshaw et al. [30], Meza et al. [39] and Swanson et al. [43], however these 4 papers are based on the same population. Both McCloskey et al. [38] and Semiz et al. [42] developed their own interview as an instrument for measuring self-injurious behaviours.

Self-report questionnaires were used for measuring self-injurious behaviours in 9 studies [17, 20, 23, 29, 33, 35, 40, 44, 45] in all. Two papers contained question(s) about self-injurious behaviours as a part of a longer questionnaire [23, 45]. Individual questionnaires as an instrument for the measurement of self-injurious behaviours can be found in 7 publications [17, 20, 29, 33, 35, 40, 44]. The Deliberate Self-Harm Inventory (DSHI) [49] appears in 3 studies [20, 35, 44]. The Functional Assessment of Self-Mutilation (FASM) [50] was used in 2 studies [29, 40]; the original questionnaire form of SIQ [51] was not applied by any of the investigated papers. Own developed questionnaire was used in 2 papers [17, 33].

In the remaining 7 publications, some kind of institutional (health care, prison) records or national databases were the sources of the data on self-injurious behaviours [12, 14, 16, 24, 25, 27, 37]. It is important to highlight the work of Kirkcaldy et al. [37]: although they based their examinations on the health records of German adolescents and youths, in the region where their study was conducted, the German Inventory Questionnaire – which contains questions about SIB – is a regular part of the documentation.

Epidemiological data about self-injurious behaviours in different groups can be found in 20 publications (see details below).

Six studies examined the normal population [15, 20, 23, 33, 36, 45]. Among them 3 papers used the term DSH and found the prevalence rates between 2.9 and 41.9% [15, 20, 33]. NSSI was a term in 2 publications: with prevalence rates of 6% [36] and 15% [45]. Evren et al. [23] used the term ‘self-harm’, and found its prevalence to be 14.3%.

Five studies investigated general psychiatric populations (inpatients, outpatients or intensive home-based treatment population) [17, 24, 34, 37, 41]. Among them only one paper used NSSI as a term: Jacobson et al. [34], however they also used DSH to include suicidal behaviour, and they found 13% prevalence of NSSI and 17% of DSH. Feingold et al. [24] investigated ‘self-injury’, and found its prevalence to be 32.4%. Kirkcaldy et al. [37] examined SIB with a prevalence rate of 59%. Preyde et al. [41] studied ‘self-harm’ and found 34% as its prevalence rate. ‘Self-mutilation’ was the term in the study of Zlotnick et al. [17], and the prevalence rate was 33.2%.

In the study of Carli et al. [19] there was an incarcerated population. They found the prevalence of ‘self-mutilation’ to be 17.0%.

In the remaining 8 studies, the aim of the investigation was to compare a group having a specific psychopathology with a healthy control group or with a group having another psychopathology.

Four publications examined attention deficit hyperactivity disorder (ADHD) as a group with specific psychopathology [12, 18, 30, 31]. Among ADHD patients versus non-ADHD patients, there was a robust difference in the prevalence rates of self-injurious behaviours. Prevalence of self-injury was 50.6% in the combined type of ADHD, versus 28.9% in the inattentive type of ADHD, versus 19% in the non-ADHD control group [30]. Prevalence of self-injury among drug dependent patients with ADHD was 47.7%, versus 25.2% without ADHD [18]. Prevalence of DSH was 69% in an ADHD group and 32% in a control group [31]. In one study there was a significant difference in the incidence of DSP: it was 6.13/10,000 persons/years in the ADHD group and 1.36/10,000 persons/years in the control group [12].

Two studies examined intermittent explosive disorder (IED) as a specific psychopathology. McCloskey et al. [38] found the prevalence of SIB to be 16% in this group. Jenkins et al. [35] investigated participants with personality disorder with or without IED: they found the prevalence of NSSI to be 18%.

Only in one publication could data be found on the prevalence of self-mutilation among participants with conduct disorder (CD) [32]: they found its prevalence between 15.5 and 62.5%. It depends on the gender and alcohol dependence of participants, with the lowest prevalence being among non-alcohol-dependent boys, and the highest being among alcohol-dependent girls. However there was another study, which examined the prevalence of SIB among psychiatric offenders in a military institution with antisocial personality disorder [42]: the prevalence rate of SIB was 92.0%.

Fifteen publications investigated the associations between self-injurious behaviours and ADHD [12, 14, 16, 18, 21, 23, 25, 28, 30, 31, 33, 41‐44]. Four of them studied ADHD versus non-ADHD groups, and found robust differences in the prevalence or incidence rates of self-injurious behaviours (self-injury [18, 30]; DSH [31]; DSP [12]). Higher symptom severity or higher scores on ADHD symptom scales or higher numbers of ADHD symptoms are associated with self-injurious behaviour in 6 papers: ADHD scores were higher in the SII group than in the control group or depressed group [21]; ADHD scores were higher in the self-harm group versus non-self-harm group [23]; and in the DSH group versus non-DSH group [33]; frequency of SIB was correlated with the number of ADHD symptoms [42]; those who engaged in self-harm in a residential treatment or intensive home-based treatment programme had higher ADHD symptom severity than those who did not engage in this behaviour [41]; and there was a significant association between symptom severity of ADHD and history of DSH behaviours [44]. Moreover, Fulwiler et al. [25] found the importance of childhood ADHD in adulthood self-mutilation among prisoners. Lam et al. [14] underline that the odds ratio of having comorbid attention deficit disorder (ADD) is 3 times higher in the self-harm group than in the non-self-harm group. Swanson et al. [43] found that both the inattentive and combined type of ADHD were associated with NSSI, however more severe forms and higher frequency of NSSI are more likely to be associated with the combined type. Young et al. [16] emphasize that the number of critical incidents (including self-injury) were higher among people with ADHD in an incarcerated population. According to the work of Guendelman et al. [28], maltreatment is a strong risk factor of both NSSI and any other self-harm acts (suicide attempts), and there is no significant difference in this risk effect between girls diagnosed with ADHD and comparison group.

Twelve publications examined the possible connection between conduct disorder (CD) or CD symptoms or antisocial personality disorder in adulthood and self-injurious behaviours [11, 15, 20‐22, 26, 32, 34, 36, 37, 40, 42]. Seven of them found significant positive associations: CD is a risk factor of adulthood DSP repetition [11]; both CD and oppositional defiant disorder (ODD) correlated with DSH, however there is no significant difference in the level of correlation between them [20]; there were higher CD scores in the SII group than in the control group or depressed group [21]; antisocial personality disorder is a risk factor of suicidal gestures (included self-injurious behaviour) [26]; prevalence of self-mutilation is high among CD patients, especially when they are girls and they are also alcohol-dependent [32]; higher initial levels of conduct problems are associated with NSSI [36]; and DSH is linked to violent behaviours (robbery, intimate partner violence, forced sex, cruelty to animals, use of a weapon) [15]. Two publications described a non-significant positive connection: CD symptoms are more frequent in a non-suicidal self-harm group than in the control group [22]; frequency of any disruptive behaviours was higher both in DSH and in NSSI groups than in the control group [34]. Nock et al. [40] found the presence of CD to be 49.4% in their 100% NSSI sample. Semiz et al. [42] found the prevalence of SIB to be 92% in a 100% antisocial personality disorder sample. However Kirkcaldy et al. [37] could not find any association between SIB and disruptive behaviour.

Four papers studied the link between oppositional defiant disorder (ODD) and self-injurious behaviours or SIB. Cerutti et al. [20] found, that ODD correlated with DSH but they did not find a significant difference with the correlation of CD and DSH. In the study of Crowell et al. [21], there are higher ODD scores in the SII group than in the depressed group or control group. Guertin et al. [29] found that ODD was more common in both the self-mutilator and suicide attempter group than in the suicide attempter only group. In Nock et al. [40], in the 100% NSSI sample the presence of ODD was 44.9%.

There are 3 publications that strengthen the relationship between intermittent explosive disorder and self-injurious behaviours (NSSI [35]; SIB [38]; self-mutilation [17]).

There was information about general externalizing symptoms in 5 publications. Crowell et al. [13] examined parasuicidal versus non-parasuicidal groups; in the parasuicidal group the T-scores of externalizing symptoms were significantly higher. Crowell et al. [21] investigated the SII group, control group and depressed group: T-scores of externalizing psychopathology were also significantly higher in the SII group than in the control or depressed groups. In the 100% NSSI sample of Nock et al. [40] the presence of any externalizing disorder was 62.9% while the presence of any internalizing disorder was 51.7%. Feingold et al. [24] did not study the direct link between externalizing pathology and self-injury, but they found a strong link between alcohol abuse and self-injury, and also described the association between externalizing pathology and alcohol abuse. Gatta et al. [27] examined neuropsychiatric inpatients who engaged in NSSI and controls from high schools. They found significantly higher externalizing scores in the NSSI group than in the control group according to both self-report and parent-report.

In the remaining 3 studies, the authors examined traits of externalizing psychopathology: Carli et al. [19] found a significant difference in the prevalence of self-mutilation between high-impulsive and low-impulsive groups. You et al. [45] investigated the role of impulse-control problems in the frequency and severity of NSSI and found individuals with more impulse-control problems had more severe and frequent NSSI behaviour. Meza et al. [39] found the importance of response inhibition in the prediction of NSSI among individuals with or without ADHD.

In total 8 of the 35 articles assessed the relationship between self-injury and suicide [22, 25, 26, 29, 31, 32, 34, 43]. To compare results by age groups, we will first overview 3 papers that studied adult samples [22, 25, 26] and then turn to the other 4 studies that assessed adolescence populations [29, 31, 32, 34] and one longitudinal study that assessed young girls (M = 9.1 years) with 5 and 10 years follow-ups [43].

In their study on adult injecting drug users, Darke and Torok [22] assessed if the two phenomena (NSSI and suicidality) overlap. They found that 42.3% of those who reported NSSI also reported suicide attempt, and 39% of those who reported suicide attempt had also engaged in NSSI. In 83.3% of the cases with both suicidal and NSSI, the NSSI was present prior to suicide attempts.

The other two studies on adult samples focused on the differences between suicidal and NSSI behaviours [25, 26].

In an adult prisoner sample, Fulwiler et al. [25] found differences between those committing suicide attempts and self-mutilation regarding their methods (more lethal methods in suicide attempt) and frequency (higher frequency in case of self-mutilation). The two groups also differed in psychiatric comorbidities: diagnosis of an affective disorder was present in 87% of the suicide attempt group compared to 19% in self-mutilators, while a syndrome of mixed anxiety/dysthymia patterns present from childhood or adolescence (56% in self-mutilation group) and history of childhood hyperactivity (75% vs 7%) characterized the self-mutilation group.

Garcia-Nieto et al. [26] also focused on the differences between self-injurers with and without intent to die. Their results pointed out the differences in the prevalence of certain personality disorders: histrionic personality disorder (HPD) (0% in neither gestures nor attempts; 46.7% in gestures; 1.6% in attempt, 12.5% in attempts + gestures group) and antisocial personality disorder (APD) (5.3% in neither gestures nor attempts; 6.7% in gestures; 4.8% in attempt, 1.2% in attempts + gestures group) as risk factors were associated with suicide gestures. Narcissistic personality disorder (NPD) (27% in suicide attempt group, 0% in all other groups) showed association with suicide attempts, and BPD (7% in neither gestures nor attempts; 33.3% in gestures, 9.7% in attempts, 43.8% in gesture + attempt group) seemed to be a risk factor for both suicide gestures and attempts.

In an adolescent community sample [31], those with ADHD reported more suicidal ideation (57% vs. 28%, P < 0.001) and DSH (69% vs. 32%, P < 0.001) than those who did not have the disorder. Female gender and depression/anxiety were also associated with both suicidal ideation and DSH, while behavioural disorder, substance use and certain family factors (e.g. living in non-intact family, living in family with financial problems) were associated with DSH but not with suicidal ideation and acts.

In an adolescent inpatient sample, those who not only had a history of suicide attempt but also a history of self-mutilative behaviour were significantly more likely to have a diagnosis of ODD (χ2₁(N = 75) = 3.91, p < .05); major depressive disorder (MDD; χ2₁(N = 76) = 13.74, p < .01;) and dysthymia (χ2₁ (N = 76) = 4.82, p < 0.05), and had higher scores of loneliness (F = 8.24, p < 0.05), anger (F = 11.88, p < 0.05), risk taking (F = 16.31, p < 0.05) and reckless behaviour (F = 7.21, p ≤ 0.005) [29].

Jacobson et al. [34] studied an adolescent outpatients sample with no DSH (52%), NSSI only (13%), suicide attempt only (16%) and with both NSSI and suicide attempt (17%). They found that the only psychiatric diagnosis in which those engaging in NSSI differed from those who had not engaged in any type of DSH was BPD. When distinguishing between DSH groups, differences were found in the likeliness of comorbid depression, posttraumatic stress disorder (PTSD) and in the levels of suicidal ideation. Regarding MDD, with the NSSI only group as the comparison group and controlling for gender, the suicide attempt only group (odds ratio – OR =3.43; 95% CI = 1.17–10.00; p = 0.03) and the suicide attempt and NSSI group (OR = 3.55; 95% confidence interval – CI = 1.24–10.16; p = 0.02) were more likely to have depression. Regarding PTSD, when controlling for gender, participants in the suicide attempt only group (OR = 8.93; 95% CI = 1.04–76.92; p = 0.046) and the suicide attempt and NSSI group (OR = 10.09; 95% CI = 1.18–85.97; p = 0.035) were more likely to have PTSD diagnosis than those in the NSSI-only group. The NSSI-only group also reported significantly lower levels of suicidal ideation scores than the other DSH groups: Suicide attempt only (adjusted mean difference = −20.24, p < 0.001) and suicide attempt and NSSI group (adjusted mean difference = −25.92; p < 0.001). Meanwhile the two other DSH groups (suicide attempt only and suicide attempt and NSSI groups) did not significantly differ from each other regarding the rates of MDD, PTSD and the levels of suicidal ideation.

Swanson et al. [43] studied girls recruited from both a clinical and non-clinical background in their follow-up study (age at baseline: M = 9.1 years; age at Wave 2: M = 14.2 years; age at Wave 3: M = 19.6 years). According to their findings, externalizing symptoms and inhibition/impulsivity might be significant partial mediators between Wave1 ADHD and W3 NSSI scores (indirect effect – IE = 0.29; standard error – SE = 0.11; CI95 = 0.10–0.51); while Wave 2 internalizing symptoms might be a significant partial mediator of the Wave 1 ADHD Wave 2 suicide attempt linkage (IE = 0.11; SE = 0.05; CI95 = 0.03–0.25).

Ilomaki et al. [32] did not investigate the association between the two phenomena but they found that alcohol dependence was a common potential risk factor for both phenomena since it increased the risk for both suicide attempts 3.8-fold [CI95 = 1.06–13.44; p = 0.041] and self-mutilation 3.9-fold (CI95 = 1.09–13.76; p = 0.037) among adolescent girls with DSM-IV-diagnosed CD.

The main limitation of our review is the heterogeneity of both the terminology and instruments, as we mentioned above, which makes it hard to compare the results of the included papers. In most of the cases, the distinction that the act was with or without suicidal intent was clear, however, among these 35 papers there were 7 papers, where this distinction was not clarified [11‐17]. The fact that similar terms for self-injurious behaviour were also measured with multiple instruments in different studies also complicates the understanding of the topic.

A further limitation is that we may be missing some relevant papers on this topic. Firstly, because we included only articles that are written in English. Secondly, we have chosen the standard method and searched for publications in large indexed literature databases. This led to 14 papers on the topic of ADHD and self-injury, however, Allely [8] used a less conservative search method and checked ‘Google Scholar’ as well and found 15 articles on the topic of ADHD and NSSI, which is a sub-topic of our review topic. There were small differences in our keywords as well, that could also be an explanation for the differences in our findings. They used ‘self-poisoning’ as a search word as well. Finally there were 5 overlapping publications [25, 30, 31, 33, 42], but they found 9 publications that we did not (5 of them fit our inclusion criteria as well, but they had not appeared in our search) and we found 3 articles in their time window, that they had not [18, 21, 41]. The remaining 5 publications we found miss their time window [12, 14, 23, 43, 44]. In spite of all these differences in the papers, Allely [8] also concluded that ADHD and self-injury have a strong association, as we did, so these results support each other. Finally, it is important to underline that our aim was not to focus only on ADHD but on the whole spectrum of externalizing disorders.

Another methodological limitation could be that our work is a narrative review. A meta-analytic review, or a full meta-analysis would be more useful to compare the results of these very heterogenous papers. To handle this limitation and make the comparisons easier, sample sizes, design of the original studies and statistical results are presented in Table 1.

Another limitation could be that since our focus in this review was to investigate the association between NSSI and externalizing pathology, the role of externalizing problems in the relationship between NSSI and suicidality might be overrepresented, while other important factors might remain hidden. A review focusing directly on the NSSI-suicidality relationship, including two of the articles discussed in this paper [29, 34] was just recently published [56]. According to their conclusion, the two phenomena are correlated and share similar vulnerabilities and risk factors, moreover, NSSI itself is found to be a risk factor for suicidal behaviour.