ADHD - An Illustrated historical overview

Developmental comorbidity I n the majority of individuals affected by ADHD, co-existing problems as well as psychiatric and non-psychiatric comorbid disorders occur (Gillberg et al. 2004, Biederman et al. 2006). Co- morbidity often results in serious func- tional and psychosocial problems in everyday life. The expression “co-morbidity” in clinical epidemiological research was coined in the 1970s by Alvan Feinstein to denote “any additional co-existing ailment” in addition to index disease (Feinstein 1970). In the context of psy- chiatric literature, the term “comorbid- ity” was applied for the first time in the mid 1980s (e.g. Barlow et al. 1986, McGlashan 1987, Sanderson et al. 1990). Biederman and colleagues re- viewed the topic of ADHD and associ- ated disorders in 1991, using the term “comorbidity” (Biederman et al. 1991). Aims of research on comorbidity were to define more homogeneous sub- groups of patients and to contribute to an aetiology-based classification system. Different theoretical models evolved to explain possible causal links between ADHD and comorbid condi- tions (e.g. Rhee et al. 2008). “Developmental comorbidity” de- scribes the concept of the age- and development-dependent occurrence of comorbid disorders, thereby dif- ferentiating between distinct trajec- tories of symptom course (Taurines et al. 2010). Concerning temporal order of manifestation, comorbid conditions may appear before the identification of definite ADHD symptoms - as ‘‘pre- comorbidity’’. In this context, tempera- ment factors, sleep disturbance, autism spectrum disorders and atopic eczema have been described. Comorbidity may coincide with the emergence of clinically significant ADHD symptoms, as ‘‘simultaneous comorbidity’’ (e.g. developmental dys- lexia, enuresis, encopresis). However, most comorbid disorders are mani- fested after the onset of ADHD in the course of disease, including anxiety disorders, tic disorder, depression and suicidality, obsessive compulsive dis- order, conduct and substance use dis- orders, bipolar disorder, obesity and personality disorders (‘‘post-comor- bidity’’). A typical example of distinct symptom progression is the initial ap- pearance of ADHD symptoms, followed