Diagnosing Primary Progressive
Aphasia |
Aphasia is the loss or impairment of the
use of language due to brain damage. The signs of aphasia
are errors in verbal output including word-finding problems,
trouble understanding speech, and difficulty in reading and/or
writing.
Language is a "localized" brain function, meaning
that some brain regions are more important for language than
others. (In contrast, personality is mostly a non-localized
brain function.) Aphasia usually results from damage to the
left side of the brain; it is unusual for aphasia to result
from right-sided brain damage. The severity of aphasia and
prognosis for recovery depend on the volume of tissue damage
and its exact location(s), the type of injury, and whether
other parts of the brain are also damaged. The onset of aphasia
is usually sudden as the cause is most often stroke or traumatic
brain injury. Infection can also cause the rapid onset of
aphasia.
The onset of aphasia is, however, not always
sudden. "Primary Progressive Aphasia" (PPA) is one
of several labels attached to a language disorder "of
insidious onset, gradual progression and prolonged course,
in the absence of generalized cognitive impairments (at least
for a substantial period of time), due to a degenerative [brain]
condition" (Duffy). In layperson's terms, it is a slowly
worsening aphasia not due to stroke, trauma, tumor or infection.
It is sometimes called "progressive aphasia without dementia."
Mesulam, who coined the term "primary progressive aphasia,"
believes that the aphasia must exist with no significant memory,
behavioral, intellectual or visual impairments at least for
two years before one can correctly use it diagnostically.
(In some cases these other symptoms do appear later on, in
which case the diagnosis is amended.)
The type or pattern of the language disorder
may differ from patient to patient. As with aphasia secondary
to stroke, the manifestations depend on what parts of the
left hemisphere are relatively more damaged at any given point
in the illness. The initial language disturbance may be fluent
aphasia (i.e., the person may have normal or even increased
rate of word production) or non-fluent (it is an effort for
the person to speak and he or she produces fewer words). The
person may or may not have difficulty understanding speech.
Eventually, almost all patients become mute and unable to
understand spoken or written language, even if their behavior
seems otherwise normal.
The average age of onset is 60; most people
with PPA are between the ages of about 40 to 80. Men are affected
twice as often as women. About half of PPA patients have a
family history of dementia in a parent or sibling, indicating
the existence of a genetic component. Half of all people with
PPA will eventually develop cognitive or behavioral problems
consistent with a more pervasive dementia syndrome, such as
Alzheimer's disease or Fronto-Temporal-Limbic Dementia, after
an average of five years. In other people, aphasia may remain
relatively isolated or even be the sole manifestation for
as long as 15 years. In general, the longer the duration of
aphasia as an isolated symptom, the less likely that other
signs of dementia will develop.
As with other "degenerative" brain
diseases, including Alzheimer's disease, there are no totally
reliable non-invasive diagnostic tests for PPA. Whether-or-not
the aphasia is "pure", that is, unaccompanied by
other cognitive impairments, may in some cases be difficult
to establish through psychological assessments because aphasia
can affect performance on "non-language " (e.g.,
memory) portions of the test. CT scans, MRI, EEG (brain wave)
often suggest left hemispheric damage, but these tests may
also be normal even though the person has PPA. "Metabolic"
imaging studies such as single photon emission computed tomography
(SPECT), positron emission tomography (PET), and Functional
MRI indicate left hemispheric dysfunction when a person has
PPA, but other disorders with different symptoms may also
cause the same radiologic abnormalities.
The cause of PPA and other degenerative
brain disorders is unknown. A variety of brain abnormalities
in people with PPA have been seen during autopsies. These
abnormalities have involved the left hemisphere either exclusively
or to a much greater extent than the right hemisphere. Most
often, brain abnormalities are consistent with Fronto-Temporal-Limbic
Dementia (FTLD), itself a syndrome--not a single disease--with
variable symptoms and microscopic abnormalities. Although
FTLD is usually associated initially with progressive changes
in personality, sometimes it presents as PPA, personality
deterioration occurring years later. Alzheimer's disease has
been proven the cause of PPA in a minority of patients. People
with PPA due to Alzheimer's disease usually have fluent aphasia.
Although researchers are testing different
medications, as with other degenerative brain afflictions
such as Alzheimer's, there is currently no cure for PPA. Speech/language
therapy aimed at developing compensatory communication strategies
may be useful for mildly impaired, motivated patients. These
strategies may be the most helpful for those whose occupations
are not strongly dependent on verbal communication.
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