Ask an Expert: Is Logopenic PPA an FTD Disorder or Alzheimer’s Disease?



Partners in FTD Care, Fall 2020
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by Emily Rogalski, PhD

One of the biggest challenges with PPA is understanding which type of neuropathology is causing a person’s symptoms: a form of FTD or Alzheimer’s disease (AD)? One reason for this challenge is there is no one-to-one correspondence between the symptoms one experiences and the type of pathology. A neurodegenerative disorder whose primary feature is language impairment, PPA occurs when abnormal proteins implicated in AD or FTD attack the language areas of the brain. Of the three PPA subtypes, logopenic variant (lvPPA) is most commonly—but not always—associated with AD pathology, which is characterized by the accumulation of two abnormal proteins: amyloid and misfolded tau proteins in brain cells.

Knowing the underlying neuropathology causing an individual’s symptoms is important so clinicians can identify appropriate clinical drug trials and eventually, effective treatments (when they become available). Currently, knowing one’s clinical PPA subtype is insufficient for determining the underlying neuropathology causing symptoms. Emerging biomarkers including cerebrospinal fluid, amyloid PET scans and tau PET scans are being developed, which can help determine underlying neuropathology in living individuals. For now, true neuropathologic diagnosis can only be confirmed by autopsy.

Each diagnosis is accompanied by two labels: one that describes the clinical symptoms (e.g., PPA, a concise way to describe the language loss one is experiencing), and one that describes the type of
proteins implicated in causing the symptoms (e.g. AD). It is important to differentiate the terms “Alzheimer’s dementia” (a label that describes the symptoms of progressive memory loss) and “Alzheimer’s disease” (the name of the neuropathological abnormal plaques and tangles seen in the brain under the microscope after death).

Families of someone with a diagnosis of PPA during life may become confused when autopsy shows AD neuropathology. Is this a misdiagnosis? No—their loved one had the clinical symptoms of PPA (e.g. language loss), and these symptoms were caused by AD neuropathology (e.g. abnormal plaques and tangles).

Disease progression is another potential source of confusion. Neurodegenerative diseases do not stay in one location of the brain—they spread. The speed and direction of that spread is incompletely understood and variable from person to person, but is being actively studied. As the disease spreads, individuals will experience new and more severe symptoms. For some, the disease spreads to the regions of the brain that control memory; for others, the disease may spread to the frontal lobes and result in changes in personality, attention or judgment. Persons diagnosed and their families may be under the impression that PPA predominately impacts language, so the occurrence of memory loss or behavioral symptoms can cause confusion and frustration. Families can work with their clinicians, including social workers, who can help them navigate these changes.

Support groups may also be an important resource for families living with a diagnosis of PPA. Talking about PPA with others who understand the lived experience of the disease—both persons diagnosed and their loved ones—can present opportunities to learn coping strategies. While groups specifically focused on PPA can foster connections within a rare-disease community, groups focused more broadly on FTD and Alzheimer’s may also help families become aware of and prepare for behavioral and cognitive symptoms that may appear over time.

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