A longitudinal view of triggers and thresholds of suicidal behavior in depression

Recurrent brief depressive disorder (RBD) and major depressive disorder (MDD) share the same diagnostic picture of full-blown depression and are both associated with increased suicide attempt rates. However, longitudinal diagnostic shifts from RBD to MDD or vice versa, called "combined depression" (CD), have demonstrated a substantially higher risk of suicide attempts in epidemiologic and clinical studies. Following the stress-diathesis model of suicidal behavior, we compared possible triggers and thresholds for suicidal behavior among patients with RBD, MDD, and CD. RBD and MDD diagnoses were based on DSM-IV criteria. Furthermore, the goal of this study was to determine if impulsivity as an underlying factor could explain high suicide attempt rates in CD.

A structured clinical interview evaluating comorbid Axis I and II disorders and RBD and a battery of instruments assessing suicidal behavior were administered to 101 patients with RBD (N = 27), MDD (N = 33), or CD (N = 41).

Patients with CD showed significantly higher (p < .05) scores on measures of suicidal behavior in comparison with RBD and MDD patients. Together with comorbid substance abuse and marital status, CD was among the highest-ranking risk factors for suicide attempts. Impulsivity was identified as a major underlying factor, predicting 80.7% of suicide attempts.

CD seems to be an important clinical risk factor for the prediction of suicide attempts, similar to risk factors such as substance use disorders and borderline personality disorder. All of these factors share the same diathesis for increased impulsivity and suicidal ideation, which could explain comorbidity and suicidal behavior. The coexistence of a greater propensity for suicidal ideation and impulsivity in RBD might also explain why such patients are more prone to attempt suicide, even if they do not, in the case of RBD, meet the duration criteria for MDD.