How Five Different Diseases Attack Language Areas In The Brain

There are five different diseases which attack the language areas in the left hemisphere of the brain, slowly causing progressive impairments of language known as primary progressive aphasia (PPA).

PPA is a neurodegenerative disease that selectively impairs language without equivalent impairment of speech, memory, or comportment, which refers to behaviour. | Representative Image (Credit: Getty Images)

New Delhi: Researchers at Northwestern University in Illinois have found that there are five different diseases which attack the language areas in the left hemisphere of the brain, slowly causing progressive impairments of language known as primary progressive aphasia (PPA).

The study was published on Wednesday, April 20, in the journal Brain. 

What Is PPA?

PPA is a neurodegenerative disease that selectively impairs language without equivalent impairment of speech, memory, or comportment, which refers to behaviour.

In a statement issued by Northwestern University, Dr M Marsel Mesulam, the lead author of the study, said the researchers discovered each of the five diseases hits a different part of the language network. He further said that in some cases, the disease hits the area responsible for grammar, and in other cases, the area responsible for word comprehension. 

Mesulam explained that each disease progresses at a different rate and has different implications for intervention. 

As many as 118 cases of PPA were considered for the study. Thus, it is based on the largest set of PPA autopsies ever assembled. 

How Do The Diseases Attack The Brain?

In the 118 consecutive autopsies on patients with PPA, primary diagnosis was Alzheimer's disease neuropathological changes in 42 per cent, according to the study. The neuropathological hallmarks of Alzheimer's disease include lesions in the brain. 

Corticobasal degeneration or progressive supranuclear palsy neuropathology was observed in 24 per cent of the cases. Corticobasal degeneration is a rare condition which can cause gradually worsening problems with movement, speech, memory, and swallowing. Progressive supranuclear palsy is a parkinsonian disorder associated with conditions like dysarthria, which occurs when muscles used for speech become weak, and dysphagia, which is difficulty swallowing. 

In 10 per cent of the cases, Pick's disease neuropathology was found. Pick's disease is a type of frontotemporal dementia that causes a progressive loss of mental function, by affecting the frontal and temporal lobes of the brain. 

Primary diagnosis was transactive response DNA-binding proteinopathy type A [TDP(A)] in 10 per cent of the patients, and TDP(C) in 11 per cent of the cases. Transactive response DNA-binding protein is involved in processing messenger RNA molecules, which serve as the genetic blueprints for making proteins. This protein is a major pathological hallmark for frontotemporal lobar degeneration conditions with certain inclusions.

Mesulam said that the patients had been followed for more than 25 years, so this is the most extensive study to date on life expectancy, type of language impairment, and relationship of disease to details of language impairment.

Findings Of The Study

The study found that word comprehension is lost for some patients, while others lose grammar. Also, disease is often misdiagnosed in early stages, because of which many people miss the chance for treatment. 

Patients diagnosed with PPA enrolled in a longitudinal study. They were made to undergo language testing and their brain structure and brain function were imaged. 

Mesulam said that an estimated one in 100,000 people have PPA. 

According to the study, the initial symptoms of PPA can be subtle and sometimes attributed to anxiety or throat problems. 

Sometimes, specialists may fail to make a diagnosis in a timely manner. The underlying disease, in 40 per cent of cases of PPA, is a very unusual form of Alzheimer's disease. 

According to the study, it is unusual because it impairs language rather than memory. Also, it can start much earlier when the person is below 65 years of age. 

In 60 per cent of the cases, the disease which causes PPA belongs to an entirely different group of conditions called frontotemporal lobar degeneration (FTLD). Individuals with this disease may exhibit weakness, muscle loss or atrophy, tiny involuntary muscle twitches, difficulty speaking, and difficulty swallowing. 

Frontotemporal lobar degeneration conditions account for about 50 per cent of all dementias that start before the age of 65. Using new imaging and biochemical methods, accurate diagnosis can be achieved.

There are several approaches at a disease level and symptomatic level, once the underlying disease is diagnosed.

Mesulam said that the trick is to approach PPA at both levels simultaneously.

How Can Such Patients Be Treated?

A patient suffering from Alzheimer's disease can be treated with medication and channelled into clinical trials. 

According to the study, an individual having difficulty with grammar and word finding can receive targeted speech therapy. 

A different type of speech therapy would be given to people having difficulty with word comprehension. They may also receive transcranial magnetic stimulation, which is a non-invasive procedure that uses magnetic fields to stimulate nerve cells in the brain. This technique seems to work best for people having trouble with word comprehension, according to the study.

Anti-anxiety medication and behavioural therapy can be used to treat anxiety around word finding. 

What Do The Researchers Aim To Do Next?

The researchers now aim to improve diagnostic accuracy through new biomarkers in order to identify if a patient's PPA is caused by Alzheimer's disease or frontotemporal lobar degeneration. They also intend to find pharmacological treatments suitable to each disease underlying PPA and individualised interventions.

The scientists also wish to design symptomatic non-pharmacologic interventions based on the nature of language impairment. 

Non-pharmacologic interventions are associated with non-acute settings such as psychological interventions.