This patient likely has the behavioral variant type of frontotemporal dementia (FTD). This form of FTD is a clinical syndrome characterized by the insidious onset of changes in behavior, personality, and executive function. This patient demonstrates the typical features of hyperorality (as evidenced by excessive alcohol intake), loss of insight, loss of empathy, compulsive behaviors, and impaired social conduct. An early age of onset is typical for the disease. Behavioral variant FTD is the second most common cause of early-onset dementia, second only to Alzheimer disease. A family history of a related neuropsychiatric disorder is evident in approximately 40% of patients with FTD; this patient's family history of a father being institutionalized in his 50s is thus concerning. Patients with behavioral variant FTD typically do well on the Mini–Mental State Examination because executive function is not well assessed by this screening test, and this cognitive domain is most likely to be impaired in patients with FTD.

Although Alzheimer disease is the most common cause of early-onset dementia, the disease presentation in this patient is not typical for this diagnosis. On cognitive testing, patients with Alzheimer disease typically exhibit impairment on tests of learning, memory, and visuospatial function. This patient showed none of these impairments.

This patient's decline in functioning can be attributed to behavioral dysfunction rather than cognitive impairment, which is the cause of impaired functioning in patients with dementia with Lewy bodies. In addition, he lacks other supportive features of dementia with Lewy bodies, such as parkinsonism, formed visual hallucinations, fluctuating cognition, rapid eye movement sleep behavior disorder, or autonomic dysfunction.

Patients with behavioral variant FTD are frequently misdiagnosed with a psychiatric illness, such as depression, bipolar disorder, or another mood or personality disturbance, especially early in the disease course. Although this patient has a few symptoms of depression, such as apathy and loss of interest, the prominent changes in behavior and lack of additional depressive symptoms make behavioral variant FTD the more likely diagnosis.