Frontotemporal dementia (FTD) refers to a group of clinical syndromes united by their links to underlying frontotemporal lobar degeneration (FTLD) pathology. FTD most often begins in the fifth to seventh decades and is nearly as prevalent as AD in this age group. Early studies suggested that FTD may be more common in men than women, however more recent reports cast doubt on this finding. Although a family history of dementia is common, autosomal dominant inheritance is seen in only 10–20% of all FTD cases.
The clinical heterogeneity seen in both familial and sporadic forms of FTD is remarkable. Three core clinical syndromes have been described (Fig. 424-1). In the behavioral variant (bvFTD), the most common FTD syndrome, social and emotional systems dysfunction manifests as apathy, disinhibition, compulsivity, loss of empathy, and overeating, often but not always accompanied by deficits in executive control. Two forms of primary progressive aphasia (PPA), the semantic and nonfluent/agrammatic variants, are commonly due to FTLD and included under the FTD umbrella. In the semantic variant, patients slowly lose the ability to decode word, object, person-specific, and emotion meaning, whereas patients with the nonfluent/agrammatic variant develop profound inability to produce words, often with prominent motor speech impairment. Any of these three clinical syndromes, but most often bvFTD, may be accompanied by motor neuron disease (MND) (Chap. 429), in which case the term FTD-MND is applied. In addition, the corticobasal syndrome (CBS) and progressive supranuclear palsy syndrome (PSP-S) can be considered part of the FTLD clinical spectrum. Furthermore, patients may evolve from any of the major syndromes described above to have prominent features of another syndrome.
Three major frontotemporal dementia (FTD) clinical syndromes. Coronal magnetic resonance imaging sections from representative patients with behavioral variant FTD (left) and the semantic (center) and nonfluent/agrammatic (right) variants of primary progressive aphasia (PPA). Areas of early and severe atrophy in each syndrome are highlighted (white arrowheads). The behavioral variant features anterior cingulate and frontoinsular atrophy, spreading to orbital and dorsolateral prefrontal cortex. Semantic variant PPA shows prominent temporopolar atrophy, more often on the left. Nonfluent/agrammatic variant PPA is associated with dominant frontal opercular and dorsal insula degeneration.
Findings at the bedside are dictated by the anatomic localization of the disorder. Medial and orbital frontal and anterior insula degeneration predicts bvFTD. Patients with nonfluent/agrammatic PPA show dominant hemisphere lateral frontal and precentral gyrus atrophy. Anterior temporal degeneration presents with semantic variant PPA. Parietal functions such as visuospatial processing and arithmetic may remain normal late into any FTD syndrome. Many patients with nonfluent aphasia or bvFTD later develop aspects of PSP-S, as disease spreads into subcortical or brainstem structures, or CBS-like features, as disease moves into peri-rolandic cortices.