71. "I THINK I HAVE ADHD”: DIFFERENTIATING LATE-ONSET ADHD FROM MCI IN OLDER ADULTS

Introduction

Cognitive complaints in patients over the age of 65 are common and associated with underlying conditions such as depression, anxiety, or the early stages of a neurodegenerative disease. Patients meeting criteria for mild cognitive impairment (MCI) may also be misdiagnosed with attention deficit hyperactivity disorder (ADHD) due to overlapping symptoms such as difficulties with sustained attention, organization and memory. This overlap can complicate the differential diagnosis and may lead to inappropriate treatments. While studies have examined the increased risk of dementia in individuals with pre-existing ADHD, there is limited literature describing cases in which patients with a new late-onset ADHD diagnosis were later found to have a neurodegenerative disease as a better explanation for their symptoms. Accurate differentiation between MCI and ADHD is crucial for providing appropriate care and counseling for patients and their families.

Methods

We describe two cases of patients in their 70s who were initially diagnosed with ADHD after reporting subjective cognitive difficulties and undergoing neuropsychometric testing. Further evaluation, including neuroimaging, revealed cognitive impairment secondary to a neurodegenerative disease. We describe the clinical presentation, diagnostic workup, and the role of neuroimaging in clarifying the diagnosis.

Results

Patient #1 presented to a psychiatric clinic at age 75 with an 18-month history of word finding difficulties and depression, which had previously been in remission for several decades. Neuropsychometric testing one year prior to evaluation was normal across most domains, with relative areas of weakness with attention regulation and executive function, thought to be consistent with a diagnosis of ADHD with contributions from anxiety and depression. He was started on a new antidepressant in addition to Adderall. Repeat neuropsychometric testing did not indicate significant progression, and further testing was not pursued. One year later, he returned to his primary physician with worsening memory concerns and functional decline. He was evaluated by Neurology, who were concerned about cognitive impairment now in the moderate range. He underwent an FDG-PET, which demonstrated a pattern consistent with Alzheimer’s disease.

Patient #2 presented to a behavioral neurology clinic at age 77 for a second opinion regarding approximately 4 years of memory concerns. Neuropsychometric testing 6 months prior to evaluation revealed mild cognitive impairment with a mild decline in memory compared to previous testing 3.5 years earlier. He also underwent brain MRI and FDG-PET at that time, which were interpreted as normal. He was diagnosed with ADHD and started on Adderall. Subsequent neuropsychometric testing was consistent with MCI, amnestic, multi-domain. FDG-PET revealed mildly decreased FDG uptake in the left anteromedial temporal lobe and bilateral orbitofrontal regions, with an overall nonspecific pattern, though potentially related to limbic-predominant age-related TDP-43 encephalopathy. His amyloid PET was also positive, and he was found to have one copy of APOE e4. He was given the diagnosis of MCI due to a probable neurodegenerative disease and recommended to discontinue Adderall.

Conclusions

New-onset cognitive difficulties in older adults are unlikely to be due to ADHD and should prompt thorough evaluation for underlying neurodegenerative diseases or other cognitive disorders. Comprehensive assessment, including neuropsychometric testing, neuroimaging, and consistent follow-up, is essential to prevent misdiagnosis and the use of potentially inappropriate therapies such as psychostimulants.