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Frontotemporal Dementia

by Juebin Huang, MD, PhD

Frontotemporal dementia (FTD) refers to sporadic and hereditary disorders that affect the frontal and temporal lobes, including Pick disease.

FTD accounts for up to 10% of dementias. Age at onset is typically younger (age 55 to 65) than in Alzheimer disease. FTDs affect men and women about equally. Pick disease is a variant of FTD, which may be pathologically characterized by severe atrophy, neuronal loss, gliosis, and presence of abnormal neurons (Pick cells) containing inclusions (Pick bodies).

About half of FTDs are inherited; most mutations involve chromosome 17q21-22 and result in abnormalities of the microtubule-binding tau protein; thus, FTDs are considered tauopathies. Some experts classify supranuclear palsy and corticobasal degeneration with FTDs because they share similar pathology and gene mutations affecting the tau protein. Symptoms, gene mutations, and pathologic changes may not correspond to each other. For example, the same mutation causes FTD symptoms in one family member but symptoms of corticobasal degeneration in another, and Pick cells may be absent in patients with typical symptoms of Pick disease.

Symptoms and Signs

Generally, FTD affects personality, behavior, and usually language function (syntax and fluency) more and memory less than does Alzheimer disease. Abstract thinking and attention (maintaining and shifting) are impaired; responses are disorganized. Orientation is preserved, but retrieval of information may be impaired. Motor skills are generally preserved. Patients have difficulty sequencing tasks, although visuospatial and constructional tasks are affected less.

Frontal release signs (grasp, root, suck, snout, and palmomental reflexes and glabellar sign—see Approach to the Neurologic Patient:Reflexes) appear late in the disease but also occur in other dementias. Some patients develop motor neuron disease with generalized muscle atrophy, weakness, fasciculations, bulbar symptoms (eg, dysphagia, dysphonia, difficulty chewing), and increased risk of aspiration pneumonia and early death.

Frontal variant FTD

Social behavior and personality change because the orbitobasal frontal lobe is affected. Patients become impulsive and lose their social inhibitions (eg, they may shoplift); they neglect personal hygiene. Some have Klüver-Bucy syndrome, which involves emotional blunting, hypersexual activity, hyperorality (eg, bulimia, sucking and smacking of lips), and visual agnosias. Impersistence (impaired concentration), inertia, and mental rigidity appear.

Behavior becomes repetitive and stereotyped (eg, patients may walk to the same location every day). Patients may pick up and manipulate random objects for no reason (called utilization behavior). Verbal output is reduced; echolalia, perseveration (inappropriate repetition of a response), and eventually mutism occur.


Primary progressive aphasia

Language function deteriorates because of asymmetric (worse on left) anterolateral temporal lobe atrophy; the hippocampus and memory are relatively spared. Most patients present with difficulty finding words. Attention (eg, digit span) may be severely impaired. Many patients have aphasia, with decreased fluency and difficulty comprehending language; hesitancy in speech production and dysarthria are also common. In some patients, aphasia is the only symptom for 10 yr; in others, global deficits develop within a few years.

Semantic dementia is a type of primary progressive aphasia. When the left side of the brain is affected most, the ability to comprehend words is progressively lost. Speech is fluent but lacks meaning; a generic or related term may be used instead of the specific name of an object. When the right side is affected most, patients have progressive anomia (inability to name objects) and prosopagnosia (inability to recognize familiar faces). They cannot remember topographic relationships. Some patients with semantic dementia also have Alzheimer disease.


Diagnosis

  • Generally similar to diagnosis of other dementias

  • Additional clinical evaluation to differentiate from some other dementias

Diagnosis is suggested by typical clinical findings. As for other dementias, cognitive deficits are evaluated (see Dementia : Diagnosis).

CT and MRI are done to determine location and extent of brain atrophy and to exclude other possible causes (eg, brain tumors, abscesses, stroke). FTDs are characterized by severely atrophic, sometimes paper-thin gyri in the temporal and frontal lobes. However, MRI or CT may not show these changes until late in FTD. Thus, FTDs and Alzheimer disease can usually be differentiated more easily by clinical criteria. For example, primary progressive aphasia differs from Alzheimer disease in that memory and visuospatial function are preserved and syntax and fluency are impaired. PET with fluorine-18 ( 18 F)–labeled deoxyglucose (fluorodeoxyglucose, or FDG may help differentiate Alzheimer disease from FTD by showing the location of hypometabolic areas. In Alzheimer disease, these areas are located in the posterior temporoparietal association cortex and posterior cingulate cortex; in FTD, they are located in the anterior regions—in the frontal lobes, anterior temporal cortex, and anterior cingulate cortex.

Prognosis

FTDs usually progress gradually, but progression rate varies; if symptoms are limited to speech and language, progression to general dementia may be slower.

Treatment

There is no specific treatment. Treatment is generally supportive (see Dementia : Treatment).

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