Limbic-predominant age-related TDP-43 encephalopathy (LATE)
Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a common neurodegenerative disorder of elderly adults (usually >80 years old). It manifests clinically as amnestic dementia and pathologically as TDP-43 proteinopathy in limbic system structures such as the hippocampus.
Terminology
Limbic-predominant age-related TDP-43 encephalopathy (LATE) is the preferred term (and convenient initialism) according to a 2019 consensus working group report . The term encompasses several previously used terms for TDP-43-related cognitive impairment, including hippocampal sclerosis (not to be confused with mesial temporal lobe epilepsy with hippocampal sclerosis), hippocampal sclerosis dementia , hippocampal sclerosis of aging , and cerebral age-related TDP-43 with sclerosis (CARTS) .
While LATE represents the clinical disorder, the term limbic-predominant age-related TDP-43 encephalopathy-neuropathological changes (LATE-NC) refers to the pathologic findings regardless of the clinical manifestations.
Epidemiology
The prevalence increases with age, dramatically so after age 80-85 years. Based on population autopsy studies, LATE neuropathologic change is present in 20-50% of individuals older than 80 years .
Clinical presentation
Patients have cognitive impairment, usually an amnestic dementia similar to that of, and often comorbid with, Alzheimer disease. The rate of cognitive decline is usually slower than that in Alzheimer disease .
Presently no diagnostic biomarker exists for LATE and definitive diagnosis can only be established with an autopsy.
Pathology
Etiology
LATE neuropathological change is characterized by proteinopathy of TDP-43 (transactive response DNA-binding protein 43), which is also implicated in amyotrophic lateral sclerosis and most cases of frontotemporal lobar degeneration . TDP-43 is a multifunctional protein that regulates gene transcription and translation. When the protein is hyperphosphorylated in disease states, TDP-43 mislocalizes to the cytoplasm rather than the nucleus and forms inclusion bodies. Abnormal TDP-43 accumulates in not only neurons but also oligodendrocytes and astrocytes.
Location
The medial temporal lobe is predominantly affected. An autopsy staging system is proposed for describing the anatomic distribution of TDP-43 proteinopathy :
- stage 1: amygdala only
- stage 2: + hippocampus
- stage 3: + middle frontal gyrus
Other areas specifically affected include the inferior frontal, anterior temporal, and insular cortices.
The affected areas are unilateral in up to half of cases .
Immunophenotype
Immunohistochemistry using antibodies against phosphorylated TDP-43 demonstrate inclusion bodies in the nucleus and cytoplasm of affected cells .
Radiographic features
MRI
The typical finding in severe cases is hippocampal sclerosis, seen as atrophy and T2 prolongation in the hippocampus and temporal lobe white matter .
Volume loss has a rostrocaudal pattern on involvement, initially confined to the amygdala and then involving the head of the hippocampus before involving the body 4. Involvement is also often asymmetric .
Differential diagnosis
The main differential diagnosis for LATE is Alzheimer disease, which can not only mimic clinically but also be consistent with LATE. Both will demonstrate hippocampal atrophy and medial temporal lobe hypometabolism. However, LATE can be suggested if amyloid and/or tau PET biomarkers are negative . Moreover, the rate of hippocampal atrophy is more rapid in LATE, despite relatively slower clinical decline . It is also more commonly asymmetric and has a more pronounced rostrocaudal pattern of involvement .
Hippocampal sclerosis can also be seen with hypoxia or with epilepsy, but these can be distinguished clinically.
