Cooper et al (2018) note that despite high use of mood stabilisers (22.4%), the 2-year incidence of mania in individuals with intellectual disabilities is 1.1%.Reference Cooper, Smiley, Allan and Morrison¹ This is higher than in the general population. They infer that clinicians need to consider mania in their differential diagnosis, highlighting the risk of misdiagnosis. The authors specifically note the similarity of symptoms across diagnostic categories, including those for mania, attention-deficit hyperactivity disorder (ADHD) and problem behaviours.

This raises an interesting point of symptom overlap between ADHD and bipolar disorder, which, as the authors suggest, can lead to diagnostic overshadowing. However, it is possible that this overlap could result in clinicians primarily diagnosing bipolar disorder, with ADHD remaining undiagnosed. This alternative perspective could offer an explanation for the high incidence of mania in the context of high mood stabiliser use.

In Cooper et al’s (2007) original study, it is of interest that there were no individuals with ADHD identified within the cohort of mild intellectual disability.Reference Cooper, Smiley, Morrison, Williamson and Allan² Although the authors acknowledged they might not have fully identified this group, the finding is noteworthy given the average prevalence in the general population is 3.4% (range 1.2–7.3%).Reference Fayyad, De Graaf, Kessler, Alonso, Angermeyer and Demyttenaere³ This baseline comparative data used in Cooper et al’s (2018) report underlines their comments pertaining to the diagnostic challenge of mental illness in the population with intellectual disabilities.Reference Cooper, Smiley, Allan and Morrison¹

Overall, Cooper et al’s recent paper highlights a need for clinicians to be more aware of symptom overlap in the area of intellectual disabilities, particularly between ADHD and mania.Reference Cooper, Smiley, Allan and Morrison¹ By raising awareness, the apparent undercurrent of diagnostic overshadowing may be better managed.