Solving mysteries requires looking at all available clues to reach an explanation. Today’s tale in the woods is no less of a detective story; Sudre, Mangalmurti and Shaw (2018) conduct a review to understand why some children remit from attention deficit hyperactivity disorder (ADHD) whilst others do not.

The authors define remission as “no longer meeting DSM diagnostic criteria for ADHD“. According to this definition, ADHD remission ranges from 55-80% during early to late adulthood. Despite no longer meeting the diagnostic criteria, around half of those ‘remitted’ still have impairing symptoms.

Sudre et al., (2018) consider three models of remission to explain these rates:  

1. A convergence/normalisation model: The brain develops to a more typical brain function and structure by correcting earlier irregularities where the ‘remitter’s’ brain resembles a never affected brain
2. A compensation/neural reorganisation model: New brain connections develop in response to ADHD symptoms where the remitted brain is different to both brains that were never affected and those with persistent ADHD
3. A fixed anomaly model: The irregular brain features of ADHD have permanent effects on the brain despite remission and the persistent and remitted brain will be similar but different to a never affected brain.

Methods

Authors searched PubMed to identify studies using neuroimaging on adolescents or adults who had remitted from childhood ADHD. Overall, 710 journal articles were identified of which 17 were selected for the review.

Results

In the literature there were mixed findings as to whether remission from ADHD can be explained through top down cognitive processes. A previous review found that behavioural measures of top down processes including response inhibition, working memory and planning in childhood did not predict later remission from ADHD. However, recent studies have found that variations in working memory and lower response time can predict improvement in ADHD symptoms.

Convergence/normalisation model 

• Several studies supported the idea that remission results from normalisation of neural areas that control top down cognitive processes. 
• Three studies found that remission of ADHD in adulthood is linked to patterns of brain activation. Those who remit show patterns of brain activation that are similar to patterns in those who were never affected, but not those who still have ADHD. 

Compensation/neural reorganisation model

• The authors also found studies supporting the theory that compensatory processes lead to remission.
• Overall, these studies suggest that those who remit from ADHD show unique features within their cognitive control network that could compensate for ADHD symptoms. 

Fixed anomaly model

• Studies that supported the fixed anomaly model largely focused on the default mode network (DMN). The default mode network is a large network of interacting regions within the brain contributing to task performance.
• Mattfeld et al (2014) found anomalies in the DMN only in those with persistent ADHD, while those who remitted as adults had no differences in their DMN when compared to those with no history of ADHD.
• The authors suggest that anomalies within the DMN reflect adult outcome rather than childhood ADHD. 

Conclusions 

• This paper provides an overview of the cognitive and developmental models that might explain remission from childhood ADHD.
• The authors note that the findings were most compatible with the ‘convergence/normalisation’ model due to many studies finding that adults who have remitted from childhood ADHD are not different neurally from those who were never affected by ADHD. While other studies found atypical neural features in those who had remitted from childhood ADHD, indicating that some brain anomalies may persist from childhood even in those who remit.
• The authors conclude that research into remission from ADHD is still at an early stage and that no conclusions can be made as to which model best explains remission. 

Strengths

• The review included a range of studies using different types of methods which demonstrates the availability of various methodologies for future replication. 
• The authors evaluated the issues concerning the definition of remission of ADHD. This is important as, with the current definition, it overlooks individuals who may still have impairing symptoms, simply because they no longer meet diagnostic criteria. This concern has led the diagnostic criteria for ADHD to be updated in the DSM, however the studies reviewed in this paper were conducted before this change took place, which poses difficulties in the ‘remitted’ groups. 
• A thorough literature review (but not a systematic review) was provided on the current state of evidence of the three models discussed, allowing readers to have a better understanding on the potential pathways to remission for ADHD.

Limitations

• Some limitations of the review included a restriction to English language papers only, which introduces bias in the results.
• The authors only used one database to gather data. Therefore, the review is very likely to have missed other relevant data from other databases and grey literature. 
• The reviewers did not conduct a meta-analysis, although this would have been hard to do with the variety of methods used they give the lack of research as a reason.
• The review only included papers that based the definition of remission on a categorical dimension of symptom reduction in accordance to DSM-5. 
• Imaging was mainly undertaken in adulthood only, which makes it impossible to know if neural changes have occurred since childhood. 

Implications

Research should move forward using prospective/longitudinal designs to understand the course of ADHD remission from childhood to adulthood. In these studies it would be important to have brain imaging undertaken throughout. This would give a clearer picture of strength of evidence for each model. With the currently available evidence it is difficult to know whether remitters remit because their brain organisation has normalised or if there was something different to begin with and that is why they remit.  

Future reviews should try to improve upon the limitations highlighted here. Specifically they should be searching multiple databases and the grey literature. Qualitative studies may be useful in exploring personal views of remission for people with ADHD. This may help to understand how the concept of remission defined by the DSM-V affects the current findings.

Contributors

Thanks to the UCL Mental Health MSc students who wrote this blog: Athena Echave (@athena_gianne), Molly Bird (@mollybird_), Hannah Cocker (@hannahcocker), Aaliyah Ali (@aaliyaali_), Sukriti Dhingra (@sukriti_speaks!), Erin Robinson (@erin_b_robinson), Alex Perkins (@alexperkins_) and Valerie Beeston (@val_ri_b). The Lewis Group definitely win the prize for the best UCL Mental Health MSc Twitter presence!

Conflicts of interest

None.

UCL MSc in Mental Health Studies

This blog has been written by a group of students on the Clinical Mental Health Sciences MSc at University College London. A full list of blogs by UCL MSc students from can be found here, and you can follow the Mental Health Studies MSc team on Twitter.

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Links

Primary paper

Sudre, G., Mangalmurti, A., & Shaw, P. (2018). Growing out of attention deficit hyperactivity disorder: Insights from the ‘remitted’ brain. Neuroscience & Biobehavioral Reviews. 2018 Nov;94:198-209. doi: 10.1016/j.neubiorev.2018.08.010. Epub 2018 Sep 5. https://doi.org/10.1016/j.neubiorev.2018.08.010

Other references

Mattfeld, A. T., Gabrieli, J. D., Biederman, J., Spencer, T., Brown, A., Kotte, A., … & Whitfield-Gabrieli, S. (2014). Brain differences between persistent and remitted attention deficit hyperactivity disorder. Brain, 137(9), 2423-2428.