Comorbidity, co-occurrence, continuum: what's in a name?

Background Comorbidity, co-occurrence and continuum are three terms used when referring to developmental problems such as Developmental Coordination Disorder (DCD), but they can be confusing and misleading. Further, the terms can be upsetting to parents, and are not always helpful in guiding the selection of clinical interventions. Goals The main purpose of this paper is to question some of the terminology we employ when referring to DCD and other developmental problems. A secondary purpose is to discuss some of the conceptual frameworks that have been proposed that attempt to address the issue of the interrelationships among developmental problems. Approach The terminology is examined by first referring to the basic dictionary definitions. Second, data we have published that relate to the issues of co-occurrence and continuum are reviewed in light of the terminology questions. Finally, we review some alternative conceptual frameworks which more accurately describe the relationships among developmental problems. Conclusion The term 'comorbidity' has limited relevance to developmental problems, and its use is questionable. In contrast, co-occurrence and continuum are more useful terms to use in regard to developmental problems. Concepts such as atypical brain development and minor neurological dysfunction provide some possible explanations for the increased levels of co-occurrence of developmental disorders in children who are more severely affected.