Chronisch progrediente Aphasien

[Rare Dementias: Frontotemporal Dementia]

Frontotemporal dementias (FTD) are among the rare dementias. Their symptomatology is - compared to the common Alzheimer’s disease - atypical, so that in many cases it takes a long time until a correct diagnosis is made. The following article gives an overview of the clinical symptoms, genetic and neuropathological basis, diagnostics and differential diagnostics and therapy.

[Pathomechanisms and clinical aspects of frontotemporal lobar degeneration]

BACKGROUND

Frontotemporal lobar degeneration (FTLD) includes a spectrum of heterogeneous clinical and neuropathological diseases. In a strict sense this includes the behavioral variant of frontotemporal dementia (bvFTD) and primary progressive aphasia (PPA) and both variants can be associated with amyotrophic lateral sclerosis (FTD-ALS). In a broader sense FTLD also includes progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS). In recent years the strong genetic component of FTLD has become increasingly clear.

OBJECTIVE

The association between clinical presentation, neuropathology, genetics and pathophysiological mechanisms of FTLD are presented.

RESULTS

The diagnostic criteria and tools for the clinical differential diagnosis of FTLD are presented. At autopsy patients show neuronal and glial inclusions of Tau, TDP-43 or FUS. While Tau pathology is often associated with extrapyramidal symptoms, patients with TDP-43 and FUS inclusions often also show signs of ALS. Pathogenic mutations directly increase the aggregation propensity of these proteins or impair protein degradation through autophagy or the proteasome. Pathogenic mutations in most FTLD genes trigger cytoplasmic missorting and aggregation of the RNA-binding protein TDP-43 and thus lead to a nuclear loss of TDP-43 function. Microgliosis and mutations in GRN and TREM2 suggest an important role of neuroinflammation in FTLD.

CONCLUSION

There is still no causal therapy for FTLD but preclinical studies focusing on pathogenic mutations in C9orf72, GRN and Tau may lead to clinical trials soon; therefore, establishing large well characterized patient cohorts is crucial for trial readiness.

[Frontotemporal dementias]

Frontotemporal dementias (FTD) account for only 5-7% of all dementia aetiologies. However, FTD is one common form of dementia in the presenile period with a symptom onset between an age of 45 and 65 years. FTD are clinically classified into a group of rare genetic variants, the behavioural variant, primary progressive aphasias and a variant including motor neuron symptoms (FTD-MNS). In recent years the pathobiological characteristics of some FTD variants was clarified, demonstrating a pathological accumulation of TAR-DNA binding protein 43 (TDP-43) as a common pathological substrate. The revised diagnostic criteria of the behavioural variant of the FTD require at least three of six clinically discriminating features (disinhibition, apathy, loss of sympathy, perseverative behaviours, hyperorality and dysexecutive neuropsychological profile). The primary progressive aphasias are classified in a nonfluent/agrammatic variant, a logopenic variant and a semantic variant according to clinical and imaging features. Movement disorders and more precisely a Parkinsonian syndrome can be part of the FTD spectrum. Some clinical features overlap the clinical diagnosis of a progressive supranuclear paralysis and the corticobasal ganglionic degeneration. A causal therapy does not exist and medical treatment is directed at the patient's key symptoms. Different agents such as serotonin reuptake inhibitors, tricyclic antidepressants, atypical neuroleptics, carbamazepine, valproate, lamotrigine and when indicated also acetylcholinesterase inhibitors are potentially helpful. All together, theses medical treatments have a low level of evidence. Non-pharmacological therapies such as physiotherapy, occupational therapy, speech therapy and disease-specific education of the patient and their relatives are important to ensure a safe residential environment and daily routine.