Frontal Lobe Disorders: Frontotemporal Dementia (Pick Disease)

Frontotemporal dementia (FTD) is a neurodegenerative disorder that clinically relates to three distinct phenotypes, behavioural variant FTD, semantic dementia (SD) and progressive nonfluent aphasia (PNFA), each is associated with focal atrophy. The clinical syndromes observed in these illnesses, encompassing diverse symptoms including loss of social skills, apathy, disinhibition, repetitive and compulsive behaviours, progressive inability to represent the self and others, loss of word meaning, and inability to express oneself, are determined by injury to specific anatomical structures. Frontotemporal lobar degeneration (FTLD) is the pathological term that encompasses all three syndromes. Ubiquitin and tau are two different pathological substrates that have been implicated in these syndromes and their anatomical predilection determines the phenotype. The genetics associated with FTD have also proven to be more diverse than anticipated. These illnesses provide a unique opportunity to investigate clinicoanatomical relationships for specific symptoms. Key concepts Frontotemporal dementia (FTD) is a clinical term that encompasses a heterogeneous group of patients that share focal degeneration within the anterior frontal, temporal and insular regions. This term includes: behavioural variant of FTD (bvFTD), progressive nonfluent aphasia (PNFA) and semantic dementia (SD). Frontotemporal lobar degeneration (FTLD) is the pathological term that encompasses all three syndromes. Behavioural variant frontotemporal dementia (bvFTD) leads to a change in personality and behaviour. PNFA is a disorder of nonfluent speech and language. SD is a disorder of semantic knowledge for words. FTD is the second most common dementia in those less than 65 years of age as it accounts for 5–6% of all dementias and is responsible for up to 17% of early onset (<70 years) dementias in autopsy series. bvFTD is associated with loss of grey matter in the frontal and temporal lobes – in particular, the ventromedial frontal cortex, the posterior orbital frontal regions, the insula bilaterally and the anterior cingulate cortex. SD displays progressive anterior temporal atrophy with clinical syndrome determined by the side of the brain with the greatest atrophy. Left-predominant cases present as a fluent, anomic aphasia whereas right anterior temporal atrophy present with a behavioural syndrome characterized by a flat affect, emotional blunting and alterations in social conduct plus deficits in empathy and inability to recognize people's emotions. PNFA is characterized anatomically by left perisylvian atrophy, in particular, atrophy of the left frontal operculum (Broca areas 44, 45 and 47). FTLD can be classified into three main pathological subtypes based on the pattern of neuronal and glial inclusion: (1) Tau-positive pathology with or without inclusions (Pick disease and related disorders); (2) Tau-negative, ubiquitin (Ub)-positive inclusions (includes FTD-MND) and (3) Tau-negative, Ub-negative pathology (dementia lacking distinctive histology). Ubiquitinated inclusions make up the most common FTLD subtype seen Keywords: frontotemporal dementia; semantic dementia; progressive nonfluent aphasia; progranulin; tdp-43