Frontotemporal dementia

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Frontotemporal dementia
Classification and external resources
ICD-10 G31.0
ICD-9 331.19
OMIM 600274 105550 614260
DiseasesDB 10034
MeSH D003704
GeneReviews

Frontotemporal dementia (FTD) is a neurodegenerative disease characterized by progressive neuronal loss predominantly involving the frontal and/or temporal lobes. The disorder was first described by Arnold Pick in 1892 and was originally called Pick's disease. Second only to Alzheimer's disease (AD) in prevalence, FTD accounts for 20% of young onset dementia cases.[1] Symptoms typically manifest in late adulthood, more commonly between 55 and 65 years, approximately equally affecting men and women.[1] Common symptoms include significant changes in social and personal behavior, apathy, blunting of emotions, and deficits in both expressive and receptive language. Currently, there is no cure for FTD, but there are treatments that help alleviate symptoms.

Signs and symptoms[edit]

FTD is traditionally difficult to diagnose due to the heterogeneity of the associated symptoms. Symptoms are classified into three groups based on the functions of the frontal and temporal lobes:

  • Behavioural variant FTD (bvFTD). Behavioural symptoms include lethargy and aspontaneity on one hand, and disinhibition on the other. Apathetic patients may become socially withdrawn and stay in bed all day or no longer take care of themselves. Disinhibited patients can make inappropriate (sometimes sexual) comments or perform inappropriate acts. Patients with FTD can sometimes get into trouble with the law because of inappropriate behavior such as stealing or speeding. Recent findings indicate that psychotic symptoms are rare in FTD, possibly due to limited temporal-limbic involvement. Among FTD patients, approximately 2% have delusions, sometimes with paranoid ideation. Hallucinations are rare. These psychotic symptoms are significantly less prevalent than what is seen in AD patients, where approximately 20% have delusions and paranoia.[2]
  • Progressive nonfluent aphasia (PNFA). Patients present with a breakdown in speech fluency due to articulation difficulty, phonological and/or syntactic errors but preservation of word comprehension.
  • Semantic dementia (SD). Some patients remain fluent with normal phonology and syntax but increasing difficulty with naming and word comprehension. In addition to the semantic-aphasic symptoms, some research has indicated that those affected may experience depression, loss of inhibition, and antisocial behavior.[3]

FTD patients tend to struggle with binge eating and compulsive behaviors.[4] These binge eating habits are often associated with abnormal eating behavior including overeating, stuffing oneself with food, changes in food preferences (cravings for more sweets, carbohydrates), eating inedible objects and snatching food from others. Recent findings have indicated that the neural structures responsible for eating changes in FTD include atrophy in the right ventral insula, striatum and orbitofrontal cortex on structural MRI voxel-based morphometry (right hemisphere).[4]

Executive function is the cognitive skill of planning and organizing. Most FTD patients become unable to perform skills that require complex planning or sequencing.[5] In addition to the characteristic cognitive dysfunction, a number of primitive reflexes known as frontal release signs are often able to be elicited. Usually the first of these frontal release signs to appear is the palmomental reflex which appears relatively early in the disease course whereas the palmar grasp reflex and rooting reflex appear late in the disease course.

The following abilities in the FTD patients are preserved:[1]

The following abilities in FTD patients are affected:[1]

In rare cases, FTD can occur in patients with motor neuron disease (MND) (typically amyotrophic lateral sclerosis). The prognosis for people with MND is worse when combined with FTD, shortening survival by about a year.[6]

Pathology[edit]

Neuropathologic analysis of brain tissue from FTLD-U patients. Ubiquitin immunohistochemistry in cases of familial FTLD-U demonstrates staining of (a) neurites and neuronal cytoplasmic inclusions in the superficial cerebral neocortex, (b) neuronal cytoplasmic inclusions in hippocampal dentate granule cells, and (c) neuronal intranuclear inclusions in the cerebral neocortex (arrows). Scale bar; (a) and (b) 40 μm, (c) 25 μm, insert 6 μm.

A number of case series have now been published looking at the pathological basis of frontotemporal dementia. As with other syndromes associated with frontotemporal lobar degeneration (FTLD), a number of different pathologies are associated with FTD:

  • Tau pathology. In a healthy individual, tau proteins stabilize microtubules, which are major component of the cytoskeleton. Examples include Pick's disease, now also referred to as FTLD-tau, and other tau-positive pathology including FTDP-17, corticobasal degeneration, and progressive supranuclear palsy. Approximately 50% of FTD cases will present with tau pathology at post-mortem.
  • TDP-43 pathology. Previously described as dementia with ubiquitin positive, tau- and alpha-synuclein negative inclusions with and without motor neuron degeneration. FTLD-TDP43 accounts for approximately 40% of FTD(± MND).
  • FUS pathology. Cases with underlying FUS pathology tend to present with behavioural variant FTD (bvFTD), but the correlation is by no means reliable enough to predict the post mortem pathology. FTLD-FUS represents only 5–10% of clinically diagnosed FTD. [7]
  • Dementia lacking distinctive histology (DLDH) is a rare entity and represents the remaining small percentage of FTD that cannot be positively diagnosed as any of the above at post-mortem.
  • In rare cases, patients with clinical FTD were found to have changes consistent with Alzheimer's disease on autopsy[8]
  • Evidence suggests that FTD selectively impairs spindle neurons,[9] a type of neuron which has only been found in the brains of humans, great apes, and whales.
  • Deficiencies of the micronutrients folate and B12[10] have been associated with cognitive impairment[11] in individuals with FTD. Chronic folate deficiency has also been implicated in cerebral atrophy,[12] leading to neurological impairment.

Diagnosis[edit]

Structural MRI scans often reveal frontal lobe and/or anterior temporal lobe atrophy but in early cases the scan may seem normal. Atrophy can be either bilateral or asymmetric.[1] Registration of images at different points of time (e.g., one year apart) can show evidence of atrophy that otherwise (at individual time points) may be reported as normal. Many research groups have begun using techniques such as magnetic resonance spectroscopy, functional imaging and cortical thickness measurements in an attempt to offer an earlier diagnosis to the FTD patient. Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) scans classically show frontal and/or anterior temporal hypometabolism, which helps differentiate the disease from Alzheimer's disease. The PET scan in Alzheimer's disease classically shows biparietal hypometabolism. Meta-analyses based on imaging methods have shown that frontotemporal dementia mainly affects a frontomedial network discussed in the context of social cognition or 'theory of mind'.[13] This is entirely in keeping with the notion that on the basis of cognitive neuropsychological evidence, the ventromedial prefrontal cortex is a major locus of dysfunction early on in the course of the behavioural variant of frontotemporal degeneration.[14] The language subtypes of frontotemporal lobar degeneration (semantic dementia and progressive nonfluent aphasia) can be regionally dissociated by imaging approaches in vivo.[15]

The confusion between Alzheimer's and FTD is justifiable due to the similarities between their initial symptoms. Patients do not have difficulty with movement and other motor tasks.[16] As FTD symptoms appear, it is difficult to differentiate between a diagnosis of Alzheimer's disease and FTD. There are distinct differences in the behavioral and emotional symptoms of the two dementias, notably, the blunting of emotions seen in FTD patients.[1] In the early stages of FTD, anxiety and depression are common, which may result in an ambiguous diagnosis. However, over time, these ambiguities fade away as this dementia progresses and defining symptoms of apathy, unique to FTD, start to appear.

In vivo (during life) brain imaging of tau protein aggregation, is done using [F-18]FDDNP positron emission tomography. This has provided a deeper understanding of FTD via visualizations and clinical-anatomical correlations. It may aid in providing a clinical diagnosis.

[F-18]FDDNP-PET has allowed the enhanced visualization of tauopathies in patients. Previous fluorescent microscopy studies of Alzheimer's disease (AD) brain specimens have shown that [F-18] FDDNP produces excellent visualization of interneuronal neurofibrillary tangles (NFTs).

This has aided in differentiating the tomographic signals of FTD from those of AD. Images obtained via [F-18]FDDNP-PET suggest higher frontal-lobe density of NFT compared to much higher temporal-lobe signals associated with AD.

Further, the ability of [F-18]FDDNP to detect tauopathies in vivo gives a tool for monitoring the effect of therapies to eliminate NFT accumulation.[17]

Recent studies over several years have developed new criteria for the diagnosis of behavioral variant frontotemporal dementia (bvFTD). Six distinct clinical features have been identified as symptoms of bvFTD.[18]

  1. Disinhibition
  2. Apathy/Inertia
  3. Loss of Sympathy/Empathy
  4. Perseverative/compulsive behaviors
  5. Hyperorality
  6. Dysexecutive neuropsychological profile

Of the six features, three must be present in a patient to diagnose one with possible bvFTD. Similar to standard FTD, the primary diagnosis stems from clinical trials that identify the associated symptoms, instead of imaging studies.[18] The above criteria are used to distinguish bvFTD from disorders such as Alzheimer's and other causes of dementia. In addition, the new criteria allow for a diagnostic hierarchy distinguished possible, probable, and definite bvFTD based on the number of symptoms present.

The role of orbitofrontal cortex and neuropsychological tests[edit]

The progression of the degeneration caused by bvFTD may follow a predictable course. The degeneration begins in the orbitofrontal cortex and medial aspects such as ventromedial cortex. In later stages, it gradually expands its area to the dorsolateral cortex and the temporal lobe.[19] Thus, the detection of dysfunction of the orbitofrontal cortex and ventromedial cortex is important in the detection of early stage bvFTD. As stated above, a behavioural change may occur before the appearance of any atrophy in the brain in the course of the disease. Because of that, image scanning such as MRI can be insensitive to the early degeneration and it is difficult to detect early-stage bvFTD.

In neuropsychology, there is an increasing interest in using neuropsychological tests such as the Iowa gambling task or Faux Pas Recognition test as an alternative to imaging for the diagnosis of bvFTD.[20] Both the Iowa gambling task and the Faux Pas test are known to be sensitive to dysfunction of the orbitofrontal cortex.

Faux Pas Recognition test is intended to measure one’s ability to detect faux pas types of social blunders (accidentally make a statement or an action that offends others). It is suggested that people with orbitofrontal cortex dysfunction show a tendency to make social blunders due to a deficit in self-monitoring.[21] Self-monitoring is the ability of individuals to evaluate their behaviour to make sure that their behaviour is appropriate in particular situations. The impairment in self-monitoring leads to a lack of social emotion signals. The social emotions such as embarrassment are important in the way that they signal the individual to adapt social behaviour in an appropriate manner to maintain relationships with others. Though patients with damage to the OFC retain intact knowledge of social norms, they fail to apply it to actual behaviour because they fail to generate social emotions that promote adaptive social behaviour.[21]

The other test, the Iowa gambling task, is a psychological test intended to simulate real-life decision making. The underlying concept of this test is the somatic marker hypothesis. This hypothesis argues that when people have to make complex uncertain decisions, they employ both cognitive and emotional processes to assess the values of the choices available to them. Each time a person makes a decision, both physiological signals and evoked emotion (somatic marker) are associated with their outcomes and it accumulates as experience. People tend to choose the choice which might produce the outcome reinforced with positive stimuli, thus it biases decision-making towards certain behaviours while avoiding others.[22] It is thought that somatic marker is processed in orbitofrontal cortex.

The symptoms observed in bvFTD are caused by dysfunction of the orbitofrontal cortex, thus these two neuropsychological tests might be useful in detecting the early stage bvFTD. However, as self-monitoring and somatic marker processes are so complex, it likely involves other brain regions. Therefore, neuropsychological tests are sensitive to the dysfunction of orbitofrontal cortex, yet not specific to it. The weakness of these tests is that they do not necessarily show dysfunction of the orbitofrontal cortex.

In order to solve this problem, some researchers combined neuropsychological tests which detect the dysfunction of orbitofrontal cortex into one so that it increases its specificity to the degeneration of the frontal lobe in order to detect the early-stage bvFTD. They invented the Executive and Social Cognition Battery which comprises five neuropsychological tests.

  • Iowa gambling task
  • Faux Pas test
  • Hotel task
  • Mind in the Eyes
  • Multiple Errands Task

The result has shown that this combined test is more sensitive in detecting the deficits in early bvFTD.[20]

Genetics[edit]

A higher proportion of FTD cases seem to have a familial component than more common neurodegenerative diseases like Alzheimer's disease. More and more mutations and genetic variants are being identified all the time, so the lists of genetic influences require consistent updating.

  • Tau-positive frontotemporal dementia with parkinsonism (FTDP-17) is caused by mutations in the MAPT gene on chromosome 17 that encodes the Tau protein[23] It has been determined that there is a direct relationship between the type of tau mutation and the neuropathology of gene mutations. The mutations at the splice junction of exon 10 of tau lead to the selective deposition of the repetative tau in neurons and glia. The pathological phenotype associated with mutations elsewhere in tau is less predictable with both typical neurofibrillary tangles (consisting of both 3 repeat and 4 repeat tau) and Pick bodies (consisting of 3 repeat tau) having being described (See Genetics Section of Tau Protein page).) The presence of tau deposits within glia is also variable in families with mutations outside of exon 10. This disease is now informally designated FTDP-17T. FTD shows a linkage to the region of the tau locus on chromosome 17, but it is believed that there are two loci leading to FTD within megabases of each other on chromosome 17.[24]
  • FTD caused by FTLD-TDP43 has numerous genetic causes. Some cases are due to mutations in the GRN gene, also located on chromosome 17. Others are caused by VCP mutations, although these patients present with a complex mixture of Inclusion body myopathy, Paget's disease of bone, and FTD. The most recent addition to the list is a hexanucleotide repeat expansion in intron 1 of C9ORF72. Only one or two cases have been reported describing TARDBP (the TDP-43 gene) mutations in a clinically pure FTD (FTD without MND).
  • No genetic causes of FUS pathology in FTD have yet been reported.

Management[edit]

Currently, there is no cure for FTD. Treatments are available to manage the behavioral symptoms. Disinhibition and compulsive behaviors can be controlled by selective serotonin reuptake inhibitors (SSRIs).[25] Although Alzheimer's and FTD share certain symptoms, they cannot be treated with the same pharmacological agents because the cholinergic systems are not affected in FTD.[1]

Because FTD often occurs in younger people (i.e. in their 40's or 50's), it can severely affect families. Patients often still have children living in the home. Financially, it can be devastating as the disease strikes at the time of life that is often the top wage-earning years.

Personality changes with individuals with FTD are not voluntary, so it is best not to take anything out on them personally. Managing the disease is unique to each individual, as different patients with FTD will display different symptoms, sometimes of rebellious nature.

Prognosis[edit]

Symptoms of frontotemporal dementia progress at a rapid, steady rate. Patients suffering from the disease can survive between 2–10 years. Eventually patients will need 24-hour care for daily function.[26]

CSF Leaks are a known cause of reversible frontotemporal dementia.[27]

See also[edit]

References[edit]

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