The Diagnostic Challenge of Young-Onset Dementia Syndromes and Primary Psychiatric Diseases: Results From a Retrospective 20-Year Cross-Sectional Study.

Objective: Distinguishing a dementia syndrome from a primary psychiatric disease in younger patients can be challenging and may lead to diagnostic change over time. The investigators aimed to examine diagnostic stability in a cohort of patients with younger-onset neurocognitive disorders.

Methods: A retrospective review of records was conducted for patients who were admitted to an inpatient neuropsychiatry service unit between 2000 and 2019, who were followed up for at least 12 months, and who received a diagnosis of young-onset dementia at any time point. Initial diagnosis included Alzheimer's disease-type dementia (N=30), frontotemporal dementia (FTD) syndromes (N=44), vascular dementia (N=7), mild cognitive impairment (N=10), primary psychiatric diseases (N=6), and other conditions, such as Lewy body dementia (N=30).

Results: Among 127 patients, 49 (39%) had a change in their initial diagnoses during the follow-up period. Behavioral variant FTD (bvFTD) was the least stable diagnosis, followed by dementia not otherwise specified and mild cognitive impairment. Compared with patients with a stable diagnosis, those who changed exhibited a higher cognitive score at baseline, a longer follow-up period, greater delay to final diagnosis, and no family history of dementia. Patients whose diagnosis changed from a neurodegenerative to a psychiatric diagnosis were more likely to have a long psychiatric history, while those whose diagnosis changed from a psychiatric to a neurodegenerative one had a recent manifestation of psychiatric symptoms.

Conclusions: Misdiagnosis of younger patients with neurocognitive disorders is not uncommon, especially in cases of bvFTD. Late-onset psychiatric symptoms may be the harbinger to a neurodegenerative disease. Close follow-up and monitoring of these patients are necessary.