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  • Frontotemporal Dementia Clinical Syndromes

    Distinct from Alzheimer's disease and other conditions leading to dementia, frontotemporal dementia (FTD) results in tissue loss in the frontal; anterior; medial and inferior temporal lobes including the amygdala and hippocampus; insula; and variably in subcortical structures such as the caudate, putamen, thalamus and substantia nigra. Of these regions, the frontal and anterior temporal lobes usually show the largest volume losses.

    Once considered rare, FTD is now thought to be the most common cause of early-onset dementia, after Alzheimer's disease. Patients typically present when they are between 45 and 65 years of age, and a positive family history is found in 40% of cases. FTD has been subdivided into three different diagnoses, each with a unique pattern of atrophy and early symptoms.

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    Basic Anatomy and Biology
    Genetics
    Medical Terms in FTD
  • Frontotemporal Lobar Degeneration Histological Subtypes

    Unlike Alzheimer's disease, the brain tissue of people with FTD doesn't show amyloid plaques, and neurofibrillary tangles are uncommon. Instead, brains affected by FTD show severe atrophy, gliosis (scarring), white matter loss and cellular inclusions. The brain tissue of approximately 40% of people with FTD shows tau inclusions. Tau is a neuronal protein that binds to microtubules and helps maintain the structure of neurons, while facilitating axonal transport. The classical cellular inclusion, named a “Pick body” in 1911, stains positively for tau. Corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are two other pathological diagnoses where tau inclusions are seen in neurons and glia. Often, patients with bvFTD or PNFA end up with CBD or PSP at pathology.

    The other major histological subtype of FTLD is characterized by tau-negative but TDP-43 positive inclusions. TDP-43 is a nuclear protein involved with the regulation of DNA expression. Mutations in TDP-43 can cause amyotrophic lateral sclerosis (ALS), and researchers are starting to investigate if those mutations also cause bvFTD. Nearly all patients with FTD and ALS, and most patients with semantic dementia, show these TDP-43 inclusions. Similarly, patients with a progranulin mutation (on chromosome 17) develop FTD with TDP-43 inclusions, although ALS is rarely associated with progranulin mutations.

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  • Social, Emotional and Executive Functioning

    The symptoms of bvFTD differ from those in AD in terms of social, emotional and executive functioning. Investigations of the brain substrates of behavioral changes demonstrate that the orbital frontal cortex (OFC) plays a crucial role in normal social and emotional behavior. The OFC appears to regulate behavior via a predominantly right-sided circuit that also includes the insula, anterior cingulate cortex and striatum, as impairments in social cognition in bvFTD seem to arise from a predominantly right-sided network involving OFC. Empathy is a complex cognitive and emotional process involving the ability to recognize and feel the emotional response of another individual. Empathy promotes social engagement, provides cues important for appropriate social conduct and has been shown to be lacking in bvFTD patients (Rankin et al., 2004). Rankin and colleagues (2006) demonstrated that right medial OFC volume was strongly related to loss of cognitive and emotional empathy in a sample of 123 patients with neurodegenerative disease, including 30 with bvFTD. Within the bvFTD group in particular, empathy deficits were related to decreased volume of the subcallosal gyrus, consistent with orbitofrontal damage. Gregory and colleagues (2002) showed that the related concept of theory of mind (i.e., the ability to infer other people’s mental states, thoughts, and feelings) was impaired in bvFTD, and that the degree of impairment showed a strong concordance with ventromedial frontal damage. In a study by Eslinger et al. (2006), bvFTD patients showed impairment on a test that required them to evaluate the thoughts, feelings and intentions of characters in social situations and choose the socially appropriate behavior to resolve the situation. The degree of impairment on this test was related to right OFC, right superior temporal, right occipital, and right posterior cingulate VBM-determined cortical atrophy. Alterations in eating behavior have also frequently been observed in bvFTD, and recent research by Woolley and colleagues (2007) with these patients suggests that a right orbitofrontal-insular-striatal circuit may be necessary for normal regulation of feeding and satiety.

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