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While Alzheimer's is the most common and most talked about form of dementia, there are many more. This article takes a closer look at semantic dementia, a form of dementia that initially targets language skills.

Dementia isn't, actually, a diagnosis. Rather, it's an umbrella term that refers to a wide range of neurodegenerative disorders that result in a deterioration of cognitive and memory skills, usually seen in older people. Alzheimer's is the most common form of dementia, accounting for as much as 60 to 80 percent of all dementia cases, making it the most-talked about form of dementia, and probably the first thing that comes to mind when an older friend or relative experiences symptoms that affect cognitive and memory skills. 

Here, we'll discuss sementic dementia, a type of dementia that initially affects a person's linguistic skills.

What Is Semantic Dementia?

Before we can define semantic dementia, we have to look at its "parent form of dementia": frontotemporal dementia. Frontotemporal dementia, or FTD for short, is a progressive neurodegenerative disorder that can impact a patient's movement, behavior, and linguistic skills. FTD comes in two main subtypes: 

  • Behavioral variant FTD usually initially manifests as behavioral and personality changes. Patients may lose their inhibitions and manners and become more outgoing than before. They can make inappropriate comments and display inappropriate sexual boundaries. (A friend's father told his caregiver he'd give her a dollar if she'd dance in front of her naked, to name an awkward example.) They may also become more passive and less motivated to engage in the things that interested them before, withdraw from social engagement, and become aggressive. Obsessive and repetitive behavior can be seen in patients with behavioral variant FTD too.
  • Primary progressive aphasia (PPA) initially manifests as a struggle with language skills. People with PPA may have trouble finding the right word, understanding what's said, reading, and talking. They may be unable to pronounce words correctly, unable to complete a sentence, and unable to repeat what was said to them. PPA also involves behavioral changes, but they are not the initial symptom.
Semantic dementia is a subtype of PPA. MRI images of people with PPA show that they undergo a particular pattern of atrophy — or wasting away — of the temporal lobes of the brain. This predominantly happens on the left side, and this pattern is what distinguishes semantic dementia from Alzheimer's disease. Semantic dementia is not hereditary. 

What Symptoms Can You Expect With Semantic Dementia?

As its name suggests, the symptoms of semantic dementia are initially language-related. If a loved one has semantic dementia, you will see a range of linguistic changes that may seem quite unexpected. Someone who was previously well-spoken and a book lover may encounter all kinds of trouble with the written and spoken word:
  • Difficulty choosing the right word, including saying the opposite of what was actually meant — "good", instead of "bad" for instance.
  • Speech so vague that it's hard to know what they are talking about: "Can you get the thing out of the thing?"
  • Losing understanding of what words mean, including asking for definitions of (common) words they previously knew.
  • Difficulty with reading and spelling.
  • As the symptoms worsen, patients can lose their short-term memory, fail to recognize everyday objects, and lose the ability to recognize faces, including perhaps yours.
  • Still later, symptoms of behavioral variant FTD can set in, and you can expect socially inappropriate, repetitive, and obsessive behavior.

How Is Semantic Dementia Diagnosed?

The diagnostic process should be carried out by a specialist. It starts with a detailed look at the person's medical history, their symptoms, and a physical examination that serves to rule other causes of the symptoms they are experiencing in or out. Cognitive, memory and language tests will be administered. 
Blood tests, genetic testing, and brain imaging may or may not be part of the diagnostic process, depending on where the patient lives and what condition is suspected. 
Genetic testing can be of used because approximately a third of people suffering from frontotemoral dementia have clearly identifiable genetic causses, involving the genes tau or MAPT, progranulin or GRN, and C9ORF72. Brain imaging techniques, namely MRI or CT scans, can identify the brain pattern seen in patients with frontotemporal dementia, confirming the diagnosis. If other causes are suspected, a specialist may order an electromyography (EMG) to monitor mucle activity, or a lumbar puncture. 

It's important to know that semantic dementia can coexist with other diagnoses, including parkinsonism and motor neuron disease. This is something that will affect the diagnostic process, as the specialist tries to get the full picture of what is going on in a particular patient. 

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