The Validity of Major Depressive disorder (MDD) in childhood has been well established, with the disorder now widely recognized and treated in mental health settings.1–4
Beginning with the seminal work of Kovacs et al,5,6
over the past 2 decades empirical data have shown that MDD in school-aged children (aged 6–12 years) is a serious clinical condition characterized by a relapsing course and is not merely a developmentally transient phenomenon.7,8
Longitudinal data from clinical samples of school-aged children with depression have demonstrated recurrence rates of 40% after 2 years and 70% after 5 years.5,6,9
Genetic vulnerability for MDD, the experience of stressful life events, as well as the presence of comorbid psychiatric disorders during childhood have emerged as key risk factors for depression onset and recurrence at school age as well as later in life.10–14
To date, studies of childhood MDD have focused predominantly on children aged 6 years and older. However, more than 20 years ago, data began to emerge that suggested that depression conforming to the diagnostic criteria found in the DSM-III-R
could be identified even earlier in life in preschool-aged children.15–18
Contradicting traditional developmental theory,19
which claimed that young children were too cognitively and emotionally immature to experience depressive affects, recent empirical studies using new and age-appropriate methods have identified DSM-IV
unipolar MDD in preschoolers. 20
To date, preschool MDD has been identified and described in the empirical literature in 4 large independent samples from 3 geographical sites.21–24
One epidemiological study estimates the prevalence rate of preschool MDD at 2.1%, the same rate found in school-aged children.23
In an investigation that screened preschoolers (N = 175) from both clinical and community sites, DSM-IV
MDD was identified using a structured age-appropriate psychiatric interview.22
The typical symptoms and vegetative signs of depression emerged as sensitive and specific manifestations of the disorder in preschoolers rather than as masked symptoms, such as somatic complaints or aggression, which were previously expected to characterize depression in younger children.25
However, in this investigation, a large group of preschoolers who met all DSM-IV
symptom criteria and had high depression severity and impairment failed to meet the strict 2-week duration criterion.26
This finding suggested that the strict duration criterion may not apply to such young children and should be “set aside” in preschool MDD.
Validation for preschool MDD (based on meeting all DSM-IV
symptom criteria) has been supported by the finding of a specific symptom constellation that was distinct from other psychiatric disorders and stable during a 6-month period.22
Additionally, alterations in the hypothalamic-pituitary-adrenal axis reactivity similar to those known in adults with depression, greater family history of mood disorders, as well as observational evidence of depressive affects and behaviors were detected in preschoolers with depression, providing further validation.22,25,27–30
More recent findings from a larger independent sample (N = 306) ascertained from community sites (and serving as the population for this investigation) have replicated the findings described above and have also demonstrated that preschoolers with depression display significant functional impairment evident in multiple contexts rated by both parents and teachers.24
Despite this growing body of empirical data validating preschool MDD, skepticism remains as to whether the preschool-onset form is clinically meaningful and/or specific or whether it is a transient developmental phenomenon or a nonspecific precursor of other later psychopathology. It also remains to be established whether preschool onset MDD, if not self-limited, is continuous with school-aged depression. Also unknown and of interest is whether preschool MDD has a remitting and relapsing course similar to school-aged MDD and, related to this, whether the same risk factors for recurrence or chronicity are operative. The purpose of this longitudinal study was to address these research questions.
It was hypothesized that preschool depression would show homotypic continuity over the course of 24 months, evidenced by a greater likelihood of subsequent depression when compared with rates observed in those with other psychiatric disorders and those without disorders at baseline. In addition, it was hypothesized that preschool depression would show greater homotypic rather than heterotypic continuity as evidenced by a greater likelihood of subsequent depression as opposed to other psychiatric outcomes. Furthermore, it was hypothesized that depression at baseline would predict later depression after controlling for comorbid psychiatric disorders and known risk factors. Preschool MDD was expected to have a remitting and relapsing course during 24 months. The current study also examined risk/protective factors that contribute to the course of preschool MDD. Based on the literature in older children, it was hypothesized that preschoolers with a greater family history of affective disorders, who experienced more stressful life events, or who had greater comorbidity would be at an increased risk for recurrent and more severe depressive episodes during a 24-month period.
To date, several studies have followed up preschoolers with internalizing symptoms or disorders and established stability as well as risk of poor later childhood outcomes.31,32
Furthermore, associations between temperament during the preschool period and later risk of depression in early adulthood have been demonstrated.33
However, to our knowledge this is the first available longitudinal follow-up data from a sample of 3- to 6-year-old children who met DSM-IV
MDD symptom criteria to inform the continuity and course of preschool MDD.