Late-onset attention-deficit/hyperactivity disorder as a differential diagnosis of dementia: a case report

Although adult attention-deficit/hyperactivity disorder has recently gained increased attention, few reports on attention-deficit/hyperactivity disorder in the pre-elderly or elderly have been published. Here, we present the case of a patient with attention-deficit/hyperactivity disorder who gradually developed dementia-like symptoms as she aged, which initially made her condition difficult to distinguish from early onset Alzheimer's disease. This report illustrates that some types of attention-deficit/hyperactivity disorder may be misdiagnosed as dementia.

The patient was a 58-year-old woman. Although she presented with a tendency for inattentiveness and forgetfulness since childhood, she did not have a history of psychiatric disorders prior to consultation. Around the age of 52 years, her inattentiveness and forgetfulness gradually progressed, and at 57 years of age, she became inattentive and forgetful that it interfered with her work and daily life. For example, she forgot meetings with important clients and transferred money to the wrong bank account; these failures resulted in poor management of her company. At home, she experienced increasing difficulties with remembering prior commitments with her family and misplacing items, which her family members noticed. With the encouragement of her family and employees, who worried that she was suffering from dementia, she visited our memory clinic, whereby she was suspected of having early onset Alzheimer's disease. However, neuropsychological tests and brain imaging evaluations did not reveal any significant abnormalities. After dismissing various possible diagnoses, including dementia, other organic diseases, mood disorders, and delirium, we diagnosed her with attention-deficit/hyperactivity disorder. Treatment with 18 mg of methylphenidate was initiated, and significant improvements in her symptoms were observed within a few days; for example, she stopped losing her things, was able to concentrate for long durations, and could complete more tasks than she could before treatment. Since initiating treatment, she has returned to work and has been able to perform her daily activities without difficulty.

This case supports that some patients with late-onset attention-deficit/hyperactivity disorder may gradually develop dementia-like symptoms during the pre-elderly and elderly stages of life. Therefore, clinicians should consider late-onset attention-deficit/hyperactivity disorder as a differential diagnosis of some types of dementias.