INTRODUCTION AND NOMENCLATURE

Frontotemporal dementia (FTD) is a neuropathologically and clinically heterogeneous disorder characterized by focal degeneration of the frontal and/or temporal lobes [1]. Age of onset is typically in the late 50s or early 60s, and the primary initial clinical manifestations are changes in personality and social behavior or language, progressing over time to a more global dementia. A subset of patients may also exhibit symptoms of extrapyramidal or motor neuron involvement at some point in the disease process.

For many years the clinical syndrome was known as Picks disease after Arnold Pick, who originally described the behavioral variant of this syndrome in 1892 [2]. A variety of terms to describe the clinical syndrome have ensued, including:

• Frontal lobe dementia
• Frontal lobe degeneration
• Frontotemporal lobar degeneration
• Pick complex

The preferred terminology for the clinical syndrome is frontotemporal dementia [3,4]. However, the term remains somewhat unclear. While frontotemporal dementia is often meant to encompass the entire syndrome complex that is associated with degeneration of the frontal and temporal lobes, at other times frontotemporal dementia is used to describe the behavioral variant specifically. In this topic, frontotemporal dementia will be used to describe the entire syndrome as a whole, and the behavioral variant will be specified when that subgroup is specifically described.

FTD subtypes are also subject to the use of evolving and inconsistent nomenclature. As an example, the terms frontal variant and temporal variant are often applied to behavioral variant FTD and to semantic dementia respectively. Because the implied neuroanatomic associations are not perfect, we prefer using the clinical rather than the anatomic terms to describe the clinical syndrome [5,6]. Finally, the term primary progressive aphasia originally described a series of patients with a progressive nonfluent aphasia [7]. As another syndrome characterized by a progressive fluent aphasia was increasingly recognized, some authors categorized this as a subset of primary progressive aphasia, while others, recognizing the frequent (but not invariable) presence of more extensive cognitive deficits in these patients, coined the term semantic dementia. We will use the terms progressive nonfluent aphasia and semantic dementia to describe these syndromes, recognizing that some patients may fall into an intermediate category.