Excerpt from Frontal and Temporal Lobe Dementia

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Background

Cases of elderly patients with progressive language deterioration have been described since Arnold Pick's landmark case report of 1892. This case study, "On the relationship between aphasia and senile atrophy of the brain", still serves as a frame of reference for apparently focal brain syndromes in diffuse or generalized degenerative diseases of the brain.

In 1982, Mesulam reported 6 patients with progressive aphasia, gradually worsening over a number of years, who did not develop a more generalized dementia. Since Mesulam's publication, numerous other cases have been reported. This disorder, which is currently termed primary progressive aphasia (PPA), has gained acceptance as a syndrome. Rarely, cases of isolated right frontal or temporal degeneration have been reported. These patients experience failure to recognize family members (prosopagnosia), failure to remember topographic relationships, and similar disorders.

In England, cases of frontal lobe dementia have been described with progressive dysfunction of the frontal lobes. In a series of case reports, Neary and Snowden outlined a syndrome with initial symptoms that were suggestive of psychiatric illness. However, the following frontal lobe behavioral abnormalities appeared over time: disinhibition, impulsivity, impersistence, inertia, loss of social awareness, neglect of personal hygiene, mental rigidity, stereotyped behavior, and utilization behavior (ie, tendency to pick up and manipulate any object in the environment). These descriptions included language abnormalities such as reduced speech output, mutism, echolalia, and perseveration.

In recent years, the condition described in the North American literature as PPA and that described in the European literature as frontal dementia have been combined under the diagnosis frontotemporal dementia (FTD).

Some North American authors have included under the FTD category cases in which artistic and musical abilities have actually emerged after the onset of the illness, usually in association with progressive language impairment.

Pathophysiology

The precise molecular causes of FTD and PPA remain elusive. Considerable progress has been made with regard to mutations in the tau protein that result in neurofibrillary tangles and neuronal degeneration. Other cases do not appear to have tau pathology and are more related to ubiquitin staining in the nervous system.

Frequency

United States

The exact prevalence of FTD is unknown. Some series based on brain pathology have estimated that FTD comprises as many as 10% of cases of dementia. In the United States, estimates are generally lower.

International

Studies on FTD from Lund, Sweden, and Manchester, England, estimate that FTD accounts for approximately 8% of patients with dementia. Probably the most accurate information comes from a Dutch study by Stevens et al, who reported 74 cases in a population of 15 million (ie, 5 cases per million). Among those aged 60-70 years, the prevalence was 28 cases per 100,000.

Mortality/Morbidity

FTD, like all dementing illnesses, shortens life expectancy. The exact influence on mortality is unknown. The rate of progression is variable. Patients with associated motor neuron disease tend to have much shorter life expectancy.

• The average age of onset is younger than that of Alzheimer disease (AD).
• The rate of progression from focal presentation to a more generalized dementia varies. Some patients experience only aphasia for periods exceeding 10 years, while others progress to dementia within a few years.
• In a subset of cases, motor neuron disease develops. This subgroup has a higher mortality rate from FTD than other affected patients. Swallowing difficulty and aspiration pneumonia are especially common in this subgroup of patients, but even patients with PPA can develop dysphagia late in the course of the illness.

Sex

FTD can develop at almost any age in either gender. The most complete review, compiled by Westbury and Bub, investigated 112 published cases prior to 1997; the series included 66% males and 34% females.

Age

FTD is generally believed to present at an earlier age than AD. In the 1997 review by Westbury and Bub, the mean age of onset was 59 years. The mode age was 64 years.

Please click here to view the full topic text: Frontal and Temporal Lobe Dementia