This broad category of disease has evolved and the nosology is confusing because type of selective atrophy of a cerebral lobe may be caused by several different histopathologic changes. The notion of lobar atrophy was introduced in 1892 when Arnold Pick of Prague described a special form of cerebral degeneration in which the atrophy was circumscribed (most often in the frontal or temporal lobes), with involvement of both gray and white matter; hence the term he applied was lobar rather than cortical sclerosis. In 1911, Alzheimer presented the first careful study of the microscopic changes, followed by even more complete analyses of the pathologic changes by the prominent neuropathologists of the age. The pathologic change associated may be any one of several types: Pick inclusion bodies, neurofibrillary tangles, other inclusions, or with no characteristic changes except for neuronal loss. Contrariwise, gliosis and mild spongiform changes in the superficial layers of cortex, and even typical plaque and tangle pathology, have all been associated with syndromes of gross atrophy of the frontal or temporal lobes. What has emerged since the work of Pick and of Alzheimer is that the lobar atrophies have diverse clinical and pathologic profiles.
In contrast to Alzheimer disease, in which the atrophy is relatively diffuse, the pathologic change in lobar atrophy is circumscribed and often asymmetrical. The parietal lobes are involved less frequently than the frontal and temporal lobes. The affected gyri become paper thin, resembling, in the advanced stages, the kernel of a dried walnut. The cut surface reveals not only a marked narrowing of the cortical ribbon but a grayish appearance and reduced volume of the underlying white matter. The corpus callosum and anterior commissure share in the atrophy but almost certainly as secondary phenomena. The overlying pia-arachnoid is often thickened, and the ventricles are enlarged. The preand postcentral, superior temporal, and occipital convolutions are relatively unaffected and stand out in striking contrast to the wasted parts.
The more common frontotemporal degenerations (FTDs) (to which Pick’s name was originally attached) may display any one of several pathologic changes and reflect different genetic causes but deposition of tau is probably the underlying pathology in most cases. For example, the behavioral or the aphasic variants of FTD, which are described below, may be the result of the deposition most often of tau, but also of progranulin, amyloid, or synuclein. It is not clear to us if the term “Pick disease” is worth retaining to denote a unique process aside from the unusual type that is due to deposition of argyrophilic intracytoplasmic inclusions (Pick bodies) and diffusely staining ballooned neurons (Pick cells). In other respects, it is simply one of the large group of FTDs. It is the lobar atrophy and marked changes in the underlying white matter that provide the unifying elements of this group of diseases.
The descriptive terms frontotemporal lobar atrophy and frontotemporal dementia are used by neurologists and neuropathologists to refer to a clinical syndrome that is associated with degeneration of the frontal and temporal lobes. Some of the clinical aspects of frontotemporal dementia were discussed in Chap. 20, but broadly speaking, there are 2 main types: a behavioral variant and a language (aphasic) variant, the latter being divided into semantic dementia, progressive nonfluent aphasia, and a logopenic variant, all described below.