Obsessive-compulsive disorder (OCD) is a severe, chronic neuropsychiatric illness affecting 1%–3% of children and adolescents, characterized by recurrent, distressing, unwanted thoughts (obsessions) and repetitive, ritualistic behaviors (compulsions). Although standard nomenclatures regard OCD as a unitary nosological entity, patients typically display a wide variety of obsessions and/or compulsions of varying severity. The diversity of demographic and clinical characteristics [1
], nature of OCD symptoms (predominance of obsessions or compulsions), associated comorbid disorders [3
], and response to treatment interventions [4
], suggests that important subtypes of OCD may exist. However, earlier attempts for symptom-based taxonomies have met limited success. Indeed, the categorical studies that used mutually exclusive subgroups of patients (e.g., checkers versus washers) to determine a specific relationship with clinical variables such as psychopathology, response to treatment, or genetic and neurobiologic variables were relatively uninformative, and follow-up studies reported important changes in the constellation of OC symptoms over time. In the longest follow-up study ever published, covering a period of 40 years from baseline to re-evaluation, Skoog and Skoog [5
] reported that more than half of the adult OCD patients had a qualitative change in their symptom themes. In addition, a study in children and adolescents reported drastic changes of OC symptoms over time [6
], since none of 79 juvenile patients maintained the same pattern of symptoms during the follow-up period lasting from 2 to 16 years. These two studies, which used a categorical approach [Skoog and Skoog used an idiosyncratic definition of symptom categories, whereas Rettew et al. used the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) symptom checklist], concluded that OC symptoms displayed a marked instability across time.
In contrast to these findings, more recent statistical approaches, based on factor analysis and taking into account the complexity of OC symptoms seen in patients, tended to identify dimensions that could be more effective in symptom-based taxonomies, and preliminary findings suggest that they could be more stable over time (for review, see [7
]). These studies suggest the presence of certain broad symptom domains that capture the heterogeneity of OC symptoms. Four major dimensions accounting for more than 60% of the variance have been consistently identified: the first dimension is characterized by symmetry and ordering obsessions and compulsions; the second is composed of aggressive, religious, sexual, and somatic obsessions, and checking compulsions; the third includes contamination obsessions and cleaning/washing compulsions; and the fourth comprises hoarding obsessions and compulsions [8
]. The validity of the four-factor model has gained support from studies showing that these factors: i) are characterized by specific clinical features such as sex, age at onset, comorbid tics and personality disorders [8
]; ii) are mediated by relatively distinct patterns of activation of fronto-striato-thalamic circuits [15
]; iii) represent predictors of the response to serotonin reuptake inhibitors [11
]; and finally iv) are related to different patterns of genetic transmission [16
], and could be associated with specific susceptibility loci [17
To date, only one study has investigated the longitudinal stability of this four factor structure. A preliminary prospective study in adult OCD patients reported that symptom dimensions appeared to be more stable over time in adults than previously suggested [18
]. Although there was a decrease in the intensity of dimensions, not correlated to the overall reduction of the severity of the disorder, shifts from one dimension to another were rare at six months intervals up to two years post-initial assessment. No factor analytic studies have been performed in child and adolescent populations. The only study performed to date about symptom stability in pediatric OCD was the study of Rettew et al. [6
] mentioned previously, which reported a change of symptoms over time. These findings could be due to the statistical methodology of the study, based on symptom categories rather than symptom dimensions.
In order to explore the multidimensionality of OC symptoms in pediatric patients and the temporal stability of the dimensions, we performed a factor analysis of OC symptoms in a sample of children and adolescents with OCD and investigated the course of these factors after a mean follow-up period of 3.8 ± 0.9 years. Assuming a developmental continuity of OCD over time [19
], we hypothesized that exploratory factor analysis in a sample of children and adolescents with OCD should produce similar dimensions to those reported in adult populations, and as a consequence, should show temporal stability.