Phenotypic variety in the presentation of frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a heterogeneous syndrome characterized by a progressive decline in behaviour or language associated with degeneration of the frontal and anterior temporal lobes. FTLD can be classified into three clinical syndromes based on the early and predominant symptoms: behavioural variant frontotemporal dementia (bvFTD); semantic dementia (SD); and progressive non-fluent aphasia (PNFA). Patients with bvFTD present with marked changes in personality and behaviour such as disinhibition, apathy, loss of sympathy, compulsive behaviours, hyperorality. Neuroimaging studies have highlighted frontal atrophy, hypometabolism and hypoperfusion. SD is characterized by a fluent anomic aphasia and behavioural changes with degeneration of the anterior temporal lobes. Patients with left-sided SD present with progressive loss of word knowledge and meaning about words, objects and concepts. Patients with PNFA present slow, effortful speech, impaired production and comprehension of grammar. PNFA is associated with atrophy, hypometabolism and hypoperfusion of the left perisylvian area. However, overlap between the syndromes can occur, particularly later in the course. In the absence of definitive biomarkers, the diagnosis is dependent on clinical symptoms. A new diagnostic criterion of bvFTD was published in 2011. Identification of the syndrome's core symptoms is important in clinical diagnosis.