Semantic variant Primary Progressive Aphasia (svPPA) is a neurodegenerative disorder characterized by an early semantic anomia, later progressing to a multimodality loss of semantic knowledge beyond the language domain, or a “semantic dementia”. SD may occur after the age of 65 and is usually misdiagnoses as AD, which also has semantic anomia, yet the etiology, prognosis, and management differs in several respects from AD.  Distinguishing the two has clinical significance.   

To evaluate the characteristics of late onset semantic dementia (SD) in comparison to comparably-demented patients with Alzheimer’s disease (AD).

A retrospective cohort study was conducted using clinical data from a referral-based behavioral neurology program. Forty-six patients with SD meeting criteria for Imaging-Supported svPPA and onset >65 years of age were compared to an equal number of patients with clinically probable Alzheimer disease (AD) on presenting clinical and neurobehavioral features.  Logistic regression controlled for sex, age, disease duration, education, and overall functional impairment.

Compared to the AD patients, the late-onset SD patients had a significantly greater signs of impairment of other semantic domains, particularly facial identification and olfactory recognition.  They also had greater behavioral difficulties in manic-like or hyperactive behavior, compulsivity or being stuck on an issue, disinhibition, and rigid dietary changes.  The presence of surface dyslexia did not distinguish the two groups.  Finally, both magnetic resonance imaging and positron emission tomography confirmed regional anterior temporal involvement distinct from the more medial temporal-hippocampal and posterior hypometabolism of AD.  

Late-onset SD may be more common than believed, as it is often misdiagnosed as AD. Yet, careful neurobehavioral assessment reveals clinical differences that can be confirmed on neuroimaging.  The correct differentiating of late-onset SD can alter the prognosis and management of patients with this disorder.