Unusual
form of memory loss often confused for Alzheimer's disease
By
Elizabeth Crown, Northwestern
University via Eureakalert
October
16, 2003
Alzheimer's disease is the
single most common cause of dementia, a chronically progressive brain
condition that impairs intellect and behavior to the point where customary
activities of daily living become compromised. Over 4 million Americans
have Alzheimer's disease. Its high prevalence may lead people to believe
that dementia is always due to Alzheimer's disease and that memory loss is
a feature of all dementias.
However, an article by Alzheimer's disease
expert M.-Marsel Mesulam, M.D., in the Oct. 16 issue of The New England
Journal of Medicine reports that nearly a quarter of all dementias,
especially those of presenile onset, may be caused by diseases other than
Alzheimer's disease and that some of these so-called atypical dementias
involve cognitive abnormalities in areas other than memory.
Mesulam is Ruth and Evelyn Dunbar Professor
of Psychiatry and Behavioral Sciences and professor of neurology at the
Feinberg School of Medicine and director of the Cognitive Neurology and
Alzheimer's Disease Center at
Northwestern
University
.
Mesulam described, for example, primary
progressive aphasia, an unusual dementia of unknown cause that is
characterized by a relentless loss of language but with memory relatively
preserved. Once considered a rare condition, primary progressive aphasia
is now commonly included among dementia syndromes and has been reported in
several hundred individuals.
Alzheimer's disease patients have
forgetfulness, usually accompanied by apathy. They misplace personal
objects, repeat questions and forget recent events. However, while these
patients may forget people's names, word-finding during conversation is
not a major problem.
In contrast, patients with primary
progressive aphasia come to medical attention because of the onset of
word-finding difficulties, abnormal speech patterns and glaring spelling
errors. Some patients cannot find the right words to express their
thoughts. Others cannot understand the meaning of words either heard or
seen. Still others cannot name objects in their environment.
In some patients with primary progressive
aphasia, the ability to write language may be less impaired than the
ability to speak it. Others develop agrammatism, using inappropriate word
order and misusing word endings, prepositions, pronouns, conjunctions and
verb tenses.
Language is the only area of prominent
dysfunction for at least the first two years of primary progressive
aphasia. In these patients, structural brain imaging studies do not reveal
a specific lesion, other than atrophy, that can account for the language
deficit, Mesulam said. Language difficulties may be the patient's only
symptoms for 10 to 14 years. Other cognitive impairments may emerge, but
the language deficit remains the primary feature throughout the illness
and progresses more rapidly than deficits in other areas.
Also in contrast to many patients with
Alzheimer's disease, who tend to lose interest in recreational and social
activities, some individuals with primary progressive aphasia maintain and
even intensify their involvement in complex hobbies such as gardening,
carpentry, sculpting and painting. One patient Mesulam described continued
to fly his airplane until aphasia prevented him from communicating with
ground control.
In patients with suspected primary
progressive aphasia, evaluation by a speech therapist is useful for
exploring alternative communication strategies, Mesulam said. Unlike
patients with Alzheimer's disease, who cannot retain new information in
memory, patients with primary progressive aphasia can recall and evaluate
recent events even though they may not be able to express their knowledge
verbally.
Currently, there is no effective
pharmacologic treatment for primary progressive aphasia. However, from the
vantage point of research, the condition provides a rare opportunity for
investigating the molecular mechanisms of focal neurodegeneration and the
neuropsychological organization of language function, Mesulam said.
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