While previous reports of late-onset ADHD have focused on age groups up to early adulthood, a recent case report has described an older individual who was diagnosed with ‘very late-onset’ ADHD after initially suspecting that she had dementia (Hiroyuki et al, 2020). This prompted the present observational study, which assessed the prevalence and clinical features of ADHD among patients presenting at a dementia clinic. The authors were particularly interested in understanding more about whether very late-onset ADHD could potentially be misdiagnosed as dementia.
The study included patients who were referred for the assessment of dementia at the specialty outpatient clinic for dementia at the Kumamoto University Hospital in Japan between April 2015 and March 2017. All patients underwent routine laboratory tests, neuroimaging studies and standard neuropsychological examinations. Organic illnesses that could contribute to cognitive decline (e.g. brain tumour) were ruled out, as were depression and delirium. Other factors were ruled out by identifying patients who met the following four criteria:
- Mini-Mental State Examination (MMSE)* score ≥26
- non-specific age-related or no significant findings on MRI
- no psychotic symptoms
- no neurological abnormalities.
The qualifying patients were then assessed for ADHD by two developmental disorder specialists, according to the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) diagnostic criteria.
There were 446 patients who presented at the specialty outpatient clinic for dementia; 81 qualified for assessment by the developmental disorder specialists, and seven of these were subsequently diagnosed with ADHD (1.6% of the total 446 patients).
Of the 37 patients who had presented with suspected early-onset AD, 22 were ultimately diagnosed with early-onset Alzheimer’s disease (AD), and six were ultimately diagnosed with ADHD. When these two groups were compared, the ADHD group included a higher number of patients with jobs associated with high social status (e.g. company owner, school master), and patients in this group were found to have had a statistically longer duration of education.
Examination of the seven patients with ADHD, and interviews with family members, identified four common features:
- Significantly younger age than the rest of the study population (aged 56 vs 75 years; p <0.001)
- Primarily experiencing symptoms of inattention and forgetfulness, rather than hyperactivity and impulsivity
- Inattention and forgetfulness had been present since early adulthood
- A disruptive life event had occurred up to 2 years prior to the study, most commonly related to work (e.g. over-working) or interpersonal relationships (e.g. discord with neighbour)
In terms of limitations, it is possible that some ADHD cases were missed: many patients were excluded to rule out other conditions with the potential to contribute to cognitive decline, and therefore these patients were not assessed for ADHD. Additionally, diagnoses may have been influenced by patients having limited memory of their childhood, the adequacy of medical records, and the fact that the developmental disorder specialists did not separately diagnose each patient and were fully aware of the study and its aims.
Overall, this observational study highlights ADHD as a potential differential diagnosis for older adults who present for assessment of dementia. However, the authors recognise that it can be difficult to distinguish ADHD from dementia in these patients, particularly early-onset AD. They suggest that methods need to be established to better distinguish the two conditions; for example, it may be possible to differentiate between inadvertent forgetfulness in ADHD and forgetfulness stemming from a lack of episodic memory in relatively advanced early-onset AD.
Read more about late manifestation of ADHD in older adults here
*MMSE is a 30-point questionnaire used to measure cognitive impairment (Folstein et al, 1975)
Disclaimer: The views expressed here are the views of the author(s) and not those of Takeda.
Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 1975; 12: 189-198.
Hiroyuki S, Tadashi J, Ryuji F, et al. Late-onset attention-deficit/hyperactivity disorder as a differential diagnosis of dementia: a case report. BMC Psychiatry 2020; 20: 550.
Sasaki H, Jono T, Fukuhara R, et al. Late-manifestation of attention-deficit/hyperactivity disorder in older adults: an observational study. BMC Psychiatry 2022; 22: 354.