Logopenic dementia

Logopaenic dementia is an uncommon clinical variant of Alzheimer's disease and is a subtype of primary progressive aphasia, which itself is a subtype of frontotemporal lobar degeneration (FTLD).

Terminology

It is important to note, that the terminology of and classification of these related conditions is evolving and thus variable across the literature ^2,3. Generally logopaenic dementia this considered one of three subtypes of primary progressive aphasia, along with semantic dementia and progressive non-fluent aphasia ^1-3. 

Clinical presentation

Although pathologically logopaenic dementia is believed to represent an atypical clinical presentation of Alzheimer's disease, clinical presentation is not with a deficit in short-term memory, but rather with slow speech and impairment of single word retrieval and sentence repetition. Helpful in distinguishing it from other primary progressive aphasias is a relative preservation of grammar, single-word comprehension and motor speech ^1,2. 

Diagnostic Criteriacriteria

As histological proof is rarely obtained, diagnostic criteria have been created to aid in the diagnosis 4. 

Clinical diagnosis of logopenic variant PPA

Both:

1. impaired single word retrieval in spontaneous speech and naming
2. impaired repetition of sentences and phrases

At least least 3 of:

1. speech (phonologic) errors in spontaneous speech and naming
2. spared single-word comprehension and object knowledge
3. spared motor speech
4. absence of frank agrammatism

Imaging-supported logopenic variant PPA

Both:

1. clinical diagnosis of logopenic variant PPA
2. predominantly left posterior perisylvian or parietal atrophy on MRI AND/OR predominant left posterior perisylvian or parietal hypoperfusion or hypometabolism on SPECT or PET

Logopenic variant PPA with definite pathology

Both:

1. clinical diagnosis of logopenic variant PPA
2. histopathologic evidence of a specific neurodegenerative pathology (e.g. AD, FTLD-tau, FTLD-TDP, other) OR presence of a known pathogenic mutation

Radiographic features

There is considerable overlap of logopaenic dementia with other frontotemporal lobar degeneration (FTLD) subtypes, with the main abnormalities involving the left temporal lobe. In contrast to FTLD, it is the more posterior part of the temporal lobe and parietal lobe, rather than the anterior temporal lobe and frontal lobe, which are affected. The temporoparietal distribution is a feature which echoes the fact that logopaenic dementia is a variant of Alzheimer's disease ¹. 

CT and MRI

Morphological changes in brain volume, best seen on MRI but also visible on CT, are primarily left temporal and parietal lobe volume loss ¹. 

PET

FDG-PET

Patients with logopaenic dementia demonstrate hypometabolism in the left temporal and parietal lobes ¹. 

PiB-PET

As logopaenic dementia is considered a variant of Alzheimer's disease, it is not surprising that affected patients are PiB-PET positive ¹.