Semantic Dementia

Semantic dementia (SD) is a disorder of language in which patients demonstrate a progressive deterioration of understanding words, especially nouns, and recognizing objects while other cognitive faculties remain remarkably spared. Specifically, patients with SD retain the ability to produce fluent speech, but without key words, this speech becomes increasing difficult to understand. SD patients also lose the ability to recognize the meaning of specific words, or to spontaneously name familiar, everyday objects. As with all FTDs, as the disorder progresses and the primary symptoms (in the case of SD, language deficits) worsen, the patient may also develop other FTD features, including behavioral, social, or motor difficulties.

Key Clinical Features

The hallmark of Semantic dementia is difficulty generating or recognizing familiar words. For example, when a patient is shown a picture of a cat, he can neither come up with the word “cat” nor does he recognize the word when it is provided. The patient characteristically asks “what is cat?” when it comes up in conversation or during testing. This happens for rare words first and common nouns for later stages. Verbs and abstract words are surprisingly spared.

Fluent spontaneous speech is retained. Especially in early stages of SD, patients may be able to “talk around” the meaning of a specific word they are unable to generate. In later stages they can repeat their agenda without listening to other speakers. Word-finding pauses in speech become common, and patients have difficulty naming familiar objects.

Some SD patients have problems recognizing familiar objects and faces. The presence of
this sign can help confirm the diagnosis.

Neuroimaging studies demonstrate marked loss of volume, reduced neural activity, and decreased blood flow in the left temporal lobe of SD patients. 

In later stages, clinical features usually include the typical behavioral abnormalities of FTD as described in the Overview to Frontotemporal Dementia and Behavioral Variant FTD.

Key Pathologic Features

Unlike Progressive Nonfluent Aphasia (PNFA), more patients with Semantic Dementia have had TDP-43, not abnormal tau as a dominant feature at autopsy. Some patients diagnosed with Semantic Dementia during life have had Alzheimer’s, not FTLD changes in the brain at autopsy.

Genetics

The majority of Semantic Dementia cases are not hereditary.

Treatment

As with all forms of FTD, there is no cure for Semantic Dementia, and in most cases its progression cannot be slowed. Although no medications have been proven effective specifically in FTD, many clinicians look to the medications and treatment approaches targeting behavioral disturbances as necessary.

For instance, some FTD patients benefit from selective serotonin reuptake inhibitors (SSRIs, used in treating obsessive-compulsive behaviors, such as hoarding or craving sweets). Clinicians may also recommend antioxidants, such as coenzyme Q10, which are known to slow the progression of damage to brain cells in general, but there is little evidence to support this in Semantic Dementia.

Management and Prognosis

Semantic Dementia is a progressive disorder of language. In later stages of the disorder, some SD patients will develop symptoms common to the other FTD subtypes, including behavioral, social, or motor difficulties. The language difficulty requires education for caregivers on the misunderstood nouns and gentle distraction of the agitated uncomprehending patient. Later the behavioral abnormality will require medical management and institutionalization. Average duration of illness is 8-10 years until Parkinson-like immobility and swallowing difficulties occur and lead to the end of life.

It is important for caregivers and families to think about long-term management issues and identify a team of experts who can help with difficult medical, financial and emotional challenges. It is useful to have a physician who is knowledgeable about FTD and approaches to treatment. Other medical specialists who may be helpful include: speech and language pathologists, occupational and physical therapists, neuropsychologists, nurses (especially home-care nursing), social workers, and genetic counselors.