FRONTOTEMPORAL
DEMENTIA
Frontotemporal dementia (FTD) is a heterogeneous spectrum of disorders marked by degeneration in the frontal and anterior temporal lobes, resulting in various symptoms of disturbed personality, behavior, and language. FTD is the third most common form of neuro- degenerative dementia, ranking after Alzheimer disease and dementia with Lewy bodies, accounting for perhaps 5% of all dementia cases. FTD generally presents at a younger age than Alzheimer disease and has a mean age at onset of 58 years.
Behavioral and personality changes
are prominent early features in individuals with FTD reflecting pathologic
involvement of the frontal lobes, most commonly the right hemisphere. Symptoms
include disinhibition, impulsivity, impaired judgment, and disturbed social
skills. An individual with FTD may have inappropriate behavior, such as
swearing, off-color jokes, and loss of social tact. Dietary habits may change,
and an individual may only eat certain foods, such as sweets. Prominent
personality changes are disturbing to the patient’s family, yet the patients
themselves are typically unconcerned and lack insight and empathy regarding how
these changes affect their families. Some individuals develop repetitious or
compulsive behavior. Severe amnesia and visuospatial impairment are typically
not present. In fact, many FTD patients are oriented and able to keep track of
day-to-day affairs.
The language presentation of FTD
varies, depending on the distribution of the pathology and includes
disturbances in speech fluency and comprehension. Broca’s area is located in
the inferior and middle gyri of the left frontal lobe and is involved in
generating articulation sequences that transform thoughts into statements. Neurodegeneration
affecting Broca’s area results in progressive nonfluent aphasia that is
characterized by loss of fluent speech and prominent anomia. The speech may
have a halting quality due to frequent pauses for word-finding. Circumlocutions
are common, because the patient has difficulty retrieving the concise words and
substitutes other words or statements for the desired word. Wernicke’s area in
the left temporoparietal junction mediates the sensory associations encoding
word meaning. Neurodegeneration affecting this region results in semantic
dementia, marked by early impairment in semantics (word
meaning), resulting in empty, fluent speech and a loss of speech comprehension.
Speech may be effortless and without hesitancies, but little meaningful
information is conveyed. These patients have prominent comprehension problems
(i.e., following commands) despite their fluent and effortless speech. Because
the language network prominently involved (Wernicke’s area) abuts the visual
association networks, semantic dementia may also be associated with complex visuoperceptual dysfunction, such
as prosopagnosia and visual object recognition.
Neuroimaging should be obtained to
rule out the presence of structural lesions (e.g., stroke, tumor) and may
reveal the presence of disproportionate atrophy in the frontal and temporal
lobes. Additionally, functional imaging in the form of positron emission
tomography (PET) may reveal altered metabolic activity in the frontal and temporal lobes.
