A second type, semantic dementia (aphasia), is characterized by early difficulty naming items, people, and words, followed by verbal perseveration, but fluency is retained. There is considerable difficulty in generating lists of words of a given category, such as animals. These individuals are quite aware that they are having trouble finding words. Eventually the patient loses not just the use of names of people and objects, but also their meaning, or the conceptual knowledge of the word. Some may develop severe prosopagnosia, especially if the atrophy is predominantly right sided. Memory for day-to-day events is preserved.
A third type has been proposed, logopenic aphasia, that shares most aspects of nonfluent aphasia but in which the meaning of words is retained.
According to Mesulam (2003), who has studied the condition extensively, 60 percent of these cases show no characteristic pathologic change, 20 percent have Pick bodies, and a similar proportion show the typical changes of Alzheimer disease in the affected cortical region. A clear familial tendency has not been found. Chapter 22 can be consulted for details of the aphasic disorders.
Posterior cortical atrophy This regional variant of lobar degeneration has been slightly less frequent than primary progressive aphasia in our practices. The fundamental feature is the progressive loss of the ability to interpret and use visual information. The result is progressive and ultimately severe visuospatial difficulty with a relative preservation of memory. Prosopagnosia, achromatopsia, and dyslexia emerge, or, there may be difficulty with depth perception, reaching for objects and an inordinate sensitivity to bright light. Patients under our care have initially had a vague sense of visual disorientation followed over months by difficulty in seeing or recognizing objects in front of them. Many have alexia with agraphia while others have acalculia or the other elements of the Gerstmann syndrome. Several eventually become cortically blind. The syndrome is essentially that of an apperceptive visual disturbance that includes fragments of the Balint and the Gerstmann syndromes. The average age of onset is about 60 years. The most common pathologic change in most reports has been characteristic of Alzheimer disease.
Lewy Body Dementia (Diffuse Lewy Body Disease, DLB)
Next to Alzheimer disease, diffuse Lewy body disease, or Lewy body dementia, has been the most frequent pathologic diagnosis established in many series of globally demented patients. Reports of this condition have increased steadily since the original communication by Okazaki and colleagues in 1961 (see review by Kosaka). The disease is defined by the diffuse involvement of cortical neurons with Lewy body inclusions and by an absence or inconspicuous number of neurofibrillary tangles and amyloid plaques. To some extent, increased recognition of this disorder is a result of improved histologic techniques, particularly the ability to detect ubiquitin and synuclein, main components of the Lewy body, by immunostaining. With this improved detection, has come a better definition of the clinical syndrome and its distinctions from Alzheimer and other dementias. Because the Lewy bodies in cortical neurons are not surrounded by a distinct halo, as they are in the substantia nigra in cases of Parkinson disease (see further on for discussion and photomicrograph of a typical Lewy body) they were not readily appreciated. Aggreagated α-synuclein is the main component of the Lewy body an observation that will prove important in understanding both Parkinson disease and Lewy-body dementia.
The disease in its typical form is marked by parkinsonian features, dementia, and a tendency to episodic delirium, especially nocturnally, and rapid eye movement (REM) sleep behavior disorder (described below and in Chap. 18). Diagnostic criteria have been offered by a working group, requiring 2 of 3 of the following: a parkinsonian syndrome (usually symmetric), fluctuations in behavior and cognition, and recurrent hallucinations (McKeith et al). The latest recursion of this group’s criteria emphasizes the presence of the REM sleep behavior disorder and severe neuroleptic sensitivity.