Subgroups in Pediatric Obsessive-Compulsive Disorder: Exploring Age Groups, Latent Profile Classes, and Latent Class Trajectories of Functional Impairment

Background: Pediatric obsessive-compulsive disorder (OCD) is debilitating and often chronic, associated with significant social and educational impairment as well as reduced quality of life. OCD can present with highly heterogenous symptom profiles. Although it is characterized by the functional relationship between obsessions and compulsions, the specific content of the obsessions and the topology of the compulsions varies greatly between individuals and can fluctuate over time within individuals. Identifying subgroups of children and adolescents with OCD based on symptom expression and associated features, such as comorbid psychopathology, can potentially shed additional light on common clinical presentations, offer insights regarding potential underlying transdiagnostic processes, and lead to improved specificity of care.
\nAims: The current thesis aims to identify, explore, and compare subgroups of children and adolescents based on their age at assessment, age of OCD symptom onset, duration of OCD symptoms, symptom expression, demographics, comorbid psychopathology, and long-term functional impairment treatment response. 
\nMethod: Study I examined subgroups based on age, comparing adolescents (age 12-17) and children (age 7-11), participating in an OCD treatment trial (n=269). In addition, subgroups based on age of OCD onset, prepubertal or adolescent, were compared within the older age group. Lastly, subgroups based on the duration of OCD illness were compared. The subgroups were, in all instances, compared in terms of: (1) OCD severity, (2) OCD symptom profile, (3) comorbid symptoms, and (4) OCD-related functional impairment. Study II used an aggregated international sample of 830 OCD-affected children and adolescents, presenting to OCD specialty centers. First, a factor analysis was conducted to establish a factor structure of OCD symptoms. Second, a dependent mixture model was employed to identify latent clusters representing subgroups of OCD-affected children and adolescents based on symptom factor scores, symptom severity, and the presence or absence of comorbid disorders. Third, relationships of subgroup membership with other clinically relevant variables, including the age of symptom onset, avoidance, impairment, and family accommodation were explored. Study III examined the long-term trajectory of OCD-related functional impairment during and after stepped-care treatment, in a longitudinal analysis of the same sample as used in study I. A latent class growth analysis was conducted to identify trajectories of child and adolescent self-reported OCD-related functional impairment over three years (170 weeks). Trajectory classes were compared on pretreatment characteristics. To identify predictors of trajectory class membership a multinomial logistic regression model was used. The overlap of the identified functional impairment trajectory classes with previously established OCD symptom severity trajectory classes was also explored. 
\nResults: In study I, younger children were found to have poorer level of insight, higher rates of ADHD, and disruptive disorders. The older group had higher levels of mental compulsions, miscellaneous obsessions and compulsions, and self-rated functional impairment. No differences were found in the prevalence of anxiety, tic, or depressive disorders between the age groups, nor in overall OCD severity. Defining groups by age of OCD onset and duration of illness rather than age at evaluation did not change results, with no further clear differences emerging. In study II, a six-factor model of OCD symptoms was identified and used as a basis for the dependent mixture model. Fit statistics favored a four-cluster latent class model with groups distinguished primarily by symptom expression and comorbidity type. Fit indices for three to seven cluster models were only marginally different and characteristics of the clusters remained largely stable between solutions with small clusters of distinct presentations added in more complex models. In study III, three distinct long-term functional impairment trajectory classes were identified. The largest class (70.7%) initiated treatment with lower functional impairment. This group experienced a moderate reduction in impairment, which was maintained over the long term. The second class (24.4%) initiated with higher functional impairment which rapidly diminished over time. The third and smallest class (4.9%), initiated with moderate functional impairment which remained unchanged over the study period. The classes differed on measures of OCD severity and comorbid symptoms. 
\nConclusions: Study I found fewer overall differences between the age groups than most previous studies. However, in line with extant literature, less insight, higher levels of ADHD, and more disruptive problems in younger children, and higher self-rated functional impairment in older children, was found. Rather than identifying a single classification system, the findings from study II support the utility of integrating dimensional, developmental, and transdiagnostic information in the conceptualization of OCD-affected children and adolescents. The clusters identified in study II point to the centrality of contamination concerns in OCD, relationships between broader symptom expression and higher levels of comorbidity, and the potential for complex/neurodevelopmental presentations. Study III found that most patients receiving stepped-care treatment improved and maintained low levels of impairment for over three years, regardless of initial level of impairment. However, a small subgroup, distinguished by higher levels of ADHD symptoms, remained at pretreatment levels of impairment throughout.

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