www.crossingdialogues.com/journal.htm DIALOGUES Crossing Dialogues Association To date, diagnosing Attention Defi cit Hyperactivity Disorder (ADHD) remains indeed one of the most controversial issues in contemporary psychiatry and behavioural sciences. Most of the conceptual problems regarding the validity of this diagnostic category arise from the heterogeneity of syndromal pictures and the high rate of comorbidity observed in subjects diagnosed with ADHD at all stages of the longitudinal course of the disorder (Wilens, Biederman and Spencer, 2002). In this regard, DSM 5 increased complexity by allowing a diagnosis of comorbidity between ADHD and autism spectrum disorders while these two diagnoses were mutually exclusive in DSM-IV-TR. In 2009, a very interesting dialogue on the methodological limits of scientifi c studies aimed at clarifying the nosographic status of ADHD appeared on this journal (Thurber 2009, Tait 2009, De Morais Ribeiro 2009). In both the original paper (Thurber et al. 2009) and the commentaries (Tait 2009, De Morais Ribeiro 2009) is highlighted the need for a more rigorous "bottom-up" approach based on scientifi c observation and testing in order to formulate diagnostic entities that can be both empirically valid and replicable. With respect to this, Tait questions the validity of the concept of "scientifi c method" itself (Tait, 2009), while De Morais Ribeiro and colleagues tackle the very important issue of the practical implications of a debate, yet scientifi cally pertinent, on whether ADHD is a hypothetic construct or a nosologic condition (De Morais Ribeiro and Cavalheiro da Silveira, 2009). Indeed, medicine is a practical discipline. Therefore knowledge, within a medical context, should also be applied to practical problems. For this reason, Kendell and Jablensky suggested a distinction between the concepts of "validity" and "utility" of a psychiatric diagnosis. The articulate conclusion of their paper reads: "At present there is little evidence that most contemporary psychiatric diagnoses are valid, because they are still defi ned by syndromes that have not been demonstrated to have natural boundaries. This does not mean, though, that most psychiatric diagnoses are not useful concepts. [...] statements about utility must always be related to context, including who is using the diagnosis, in what circumstances, and for what purposes." (Kendell and Jablensky, 2003). In fact it is clear that, although most diagnostic concepts in psychiatry have not proven valid, many of them are useful for clinicians for the information they are associated with (e.g. about outcome and treatment response). For example, in the case of ADHD a diagnosis in childhood/ adolescence is associated with a signifi cantly higher risk of developing a substance use disorder and with signifi cantly worse young adult educational and vocational outcomes (Mannuzza et al., 1993; Capusan et al., 2016). Furthermore, clinical response to stimulant drugs in ADHD is around 70-80% even in adults (Spencer et al., 2005), which is signifi cantly higher than response rates to pharmacological treatments usually observed in all the other neurological or Dialogues in Philosophy, Mental and Neuro Sciences Present and future trajectories towards a possible valid and useful diagnosis of ADHD P D R School of Medicine and Psychology NESMOS Department, Sant'Andrea Hospital, Sapienza University, Rome, Italy I.R.C.C.S. Fondazione Santa Lucia, Rome, Italy Email: pietro.derossi@uniroma1.it DIAL PHIL MENT NEURO SCI 2016; 9(1): 34-35 34 DIAL PHIL MENT NEURO SCI 2016; 9(1): 34-35 De Rossi, 2016 REFERENCES Capusan AJ, Bendtsen P, Marteinsdottir I, Larsson H. (2016) Comorbidity of Adult ADHD and Its Subtypes With Substance Use Disorder in a Large PopulationBased Epidemiological Study J Atten Disord. Feb 2. pii: 1087054715626511. De Morais Ribeiro VL, Cavalheiro da Silveira JC. (2009) Another look at ADHD. Dial Phil Ment Neuro Sci, 2:5253. Kendell R, Jablensky A. (2003) Distinguishing between the validity and utility of psychiatric diagnoses. Am J Psychiatry, 160:4-12. Mannuzza S, Klein RG, Bessler A, Malloy P, LaPadula M. (1993) Adult outcome of hyperactive boys. Educational achievement, occupational rank, and psychiatric status. Arch Gen Psychiatry, 50:565-576. Shaw P, Eckstrand K, Sharp W, Blumenthal J, Lerch JP, Greenstein D, Clasen L, Evans A, Giedd J, Rapoport JL. (2007) Attention-defi cit/hyperactivity disorder is characterized by a delay in cortical maturation. Proc Natl Acad Sci U S A, 104:19649-19654. Shaw P, Sharp WS, Morrison M, Eckstrand K, Greenstein DK, Clasen LS, Evans AC, Rapoport JL. (2009) Psychostimulant treatment and the developing cortex in attention defi cit hyperactivity disorder. Am J Psychiatry, 166:58-63. Shaw P, Gogtay N, Rapoport J. (2010) Childhood psychiatric disorders as anomalies in neurodevelopmental trajectories. Hum Brain Mapp, 31:917-925. Shaw P, Malek M, Watson B, Sharp W, Evans A, Greenstein D. (2012) Development of cortical surface area and gyrifi cation in attention-defi cit/hyperactivity disorder. Biol Psychiatry, 72:191-197. Shaw P, Malek M, Watson B, Greenstein D, de Rossi P, Sharp W. (2013) Trajectories of cerebral cortical development in childhood and adolescence and adult attention-defi cit/hyperactivity disorder. Biol Psychiatry, 74:599-606. Spencer T, Biederman J, Wilens T, Doyle R, Surman C, Prince J, Mick E, Aleardi M, Herzig K, Faraone S. (2005) A large, double-blind, randomized clinical trial of methylphenidate in the treatment of adults with attentiondefi cit/hyperactivity disorder. Biol Psychiatry, 57:456463. Tait G. (2009) ADHD, Truth, and the Limits of Scientifi c Method. Dial Phil Ment Neuro Sci, 2:50-51. Thurber S, Sheehan W, Roberts RJ. (2009) Attention Defi cit Hyperactivity Disorder and Scientifi c Epistemology. Dial Phil Ment Neuro Sci, 2:33-39. Wilens TE, Biederman J, Spencer TJ. (2002) Attention defi cit/hyperactivity disorder across the lifespan. Annu Rev Med, 53:113-131. psychiatric disorders. However, I reckon that Thurber and colleagues correctly pointed out that the existing brain-based causal models were not adequate to provide rigorous supporting data coming from testing falsifi able hypotheses. In this context, a re-opening of the dialogue is defi nitely warranted as new evidence on ADHD was provided since 2009. Of course, a thorough review of such evidence is not possible in a commentary. Therefore, I will focus on some important longitudinal neuroimaging studies that have helped clarify the peculiar way neuro-development unfolds in ADHD compared to typically developing subjects. Such studies, conducted on ADHD as on the other childhood psychiatric disorders, suggest that subjects with a diagnosis of ADHD which is confi rmed by repeated longitudinal assessments is associated with a peculiar anomaly of brain cortical developmental trajectories (Shaw, Gogtay and Rapoport, 2010). In particular, ADHD is characterized by a delay in cortical maturation of key brain areas, predominantly the prefrontal regions of the cerebral cortex, and this remains associated with the severity of inattentive symptoms at the transition between late adolescence and young adulthood (Shaw et al., 2007; Shaw et al., 2012; Shaw et al., 2013). Finally, in ADHD remission is associated with convergence to the template of typical development, whereas persistence is accompanied by progressive divergence away from typical trajectories both in developmental age and adulthood (Shaw et al., 2009; Shaw et al., 2013). The studies providing this evidence have been conducted by clinically assessing and scanning multiple times through childhood, adolescence and young adulthood large samples of subjects diagnosed with ADHD and typically developing subjects over a period of 20 years. Although the above described results display a high grade of "objectivity", this does not allow etiopathogenetic inferences. In fact, given the plasticity of the human central nervous system, it is impossible to conclude whether the peculiar, delayed cortical developmental trajectory seen in ADHD is pre-determined or results from a lifelong and very complex brain-environment interaction. However, the aforementioned studies are a good example of how an empirically valid approach based on scientifi c observation can be used to start validating a diagnostic concept and/ or providing therapeutic/prognostic indices. In fact, the peculiar shape of the cortical thickening and thinning process as longitudinally measured by magnetic resonance imaging has indeed a negligible probability of being infl uenced by the formal diagnosis a given subject has received. Of course these results, yet very promising, need replication, and I am more than inclined to believe that the researchers who are starting to make this possible do not disdain to adopt "Nullius in verba" as their motto.