Frontotemporal Lobar Dementias

A selective degeneration of the frontal and temporal lobes is the distinctive feature of a group of dementias estimated to comprise 15% to 20% of all dementia cases. Frontotemporal lobar dementias (FTLD) are not common, but their incidence is increasing as more cases are recognized. Individuals from early to late midlife are affected, and the clinical course averages from 5 to 15 years. Most diseases are sporadic, but familial examples with autosomal dominant inheritance also have been identified. The clinical presentation varies greatly among the diseases but all share neuropsychiatric symptoms, cognitive decline, and neurologic disorders. Neuropsy-chiatric symptoms in various combinations are usually in the foreground of the clinical picture, including behavioral and personality changes, emotional lability, depression, anxiety, restlessness, agitation, social disinhibition, and lack of initiative, planning, organizing (executive functions), insight, and judgment. Adding to the clinical picture are features of Kluver-Bucy syndrome, such as oral tendency, bulimia, and hypersexual-ity. During the course of the disease, language dysfunction with fluent or nonfluent aphasia, memory impairment, and general cognitive decline gradually progresses to severe dementia. Accompanying neurologic disorders relate to the extrapyramidal and pyramidal motor systems; they may introduce the diseases or develop during their course. MRI and CT scans of the head are helpful in demonstrating ventricular enlargement con fined to the frontal and temporal horns. PET and SPECT scans show hypometabolism in the affected regions.

The pathology has a widespread distribution. Neuronal degeneration in the frontotemporal cortex is associated with neuronal losses in the basal ganglia, midbrain, brainstem, and spinal cord, in various combinations. The neurons and glial cells display distinctive neuronal and glial inclusions that immunoreact for tau protein or ubiquitin (Table 5.6).

Frontotemporal dementias are conveniently grouped into three categories: FTLDs with tau protein pathology (Figs. 5.13 through 5.17); FTLDs with ubiquitin-only pathology (Figs. 5.18 and 5.19), and FTLDs with no distinctive pathology.

TABLE 5.6.

Frontotemporal Lobar Dementias

Molecular Pathology

Neuronal/Glial Inclusions

Tau positive Pick's disease Dementia with parkinsonism linked to chromosome 17 Dementia with cortico-basal degeneration

Neuronal Inclusions

Ubiquitin-positive Dementia with motor neuron disease

Dementia with ubiquitin-only-immunoreaction

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