Neurogenic Speech Disorders: Prevalence and Characteristics of Speech Disorders

This post defines speech disorders that are neurogenic and acquired (meaning they come on later in life due to a specific event), and how they can affect communication. Speech and language go hand in hand, and are both affected after a stroke in particular, but also after traumatic brain injury or any other neurologic trauma or disease.

Speech is how you speak – how you move your lips, tongue, and mouth to create speech sounds and combine them to form words. Cognition is coming up with thoughts that you want or need to share, and language is how we find the words to describe those thoughts in an expected, rule-following manner.

How do speech and communication work?

Communication can break down at any of these levels, and each is frustrating and difficult in its own right. Speech disorders affect how our lips, tongue, and other speech generating organs work together to produce sound. Speech is a very complex process:

1. First your brain sends the notice to your muscles to move in a certain way.
2. Your cerebellum and other monitoring parts of your nervous system monitor and adjust your speech production as sounds come out.
3. Next, you take a deep breath and then push that air past your vocal cords, which need to vibrate to make sound.
4. Then your velum (the flap between your mouth and your nose) opens or closes as appropriate for certain sounds (m, n, and “ng” are all nasal sounds, meaning that your velum is open for these sounds).Try saying “mmmm” with your hand on your nose – you’ll feel it vibrate because sound is coming out of your nose. Now try saying “dah” with your hand on your nose – you won’t feel it vibrate because sound is coming out of your mouth.
5. Finally your tongue and lips find the correct place and do the correct action for the sound you want – for example, for the sound “tuh,” you tongue has to find its correct placement on the roof of your mouth behind your front teeth and “tap,” with your lips open.

And just think, you have to do that for every sound in every word. It’s complicated.

According to the Mayo Clinic, neurogenic communication disorders have the following prevalence rates:

• 54% are dysarthria – this is a motor speech disorder that can affect many aspects of generating your voice and speech; these difficulties are due to communication difficulties between the brain and your muscles.
• 25% are aphasia – we’ve discussed aphasia at great link, but keep in mind that aphasia is a language disorder, not a speech disorder – persons with aphasia often do also have speech disorders as well.
• 16% other cognitive-language disorders – dementia, TBI, amnesia fall into this category.
• 4% have apraxia of speech – this is a speech disorder due to difficulty with motor planning and programming; often the wrong sounds come out, and prosody (the up and down lilt of a voice) is often affected – people with apraxia of speech may sound fairly robotic.
• 1% have another neurogenic speech issue, such as mutism, acquired stuttering, and others.

Dysarthria and apraxia are the two major types of speech disorders

There are many different types of Dysarthria that depend on where and what type of neurologic damage has been done. They all sound a little different, though as you’ll see some have a few common characteristics.

Flaccid type – weak muscles: 

• Sound too nasal (this is because the velum is too weak to close appropriately)
• Very breathy (in fact you can often hear someone with flaccid dysarthria inhale)
• Usually speak in short phrases
• Tire quickly but recover after resting
• Monopitch (pitch of voice does not change much)
• Monoloudness (unchanged volume), and reduced loudness

Spastic type – overly tight muscles 

• Sound too nasal (this is because the velum is too weak to close appropriately)
• Usually speak in short phrases
• Harsh, strained/strangled vocal quality
• Low pitch
• Slow rate
• Monopitch (pitch of voice does not change much)
• Monoloudness (unchanged volume), and reduced loudness Intermittent breathy segments

Hypokinetic– usually associated with Parkinson’s; have a hard time getting going and sustaining: 

• Sound too nasal (this is because the velum is too weak to close appropriately)
• Breathy voices
• Teloscoping of syllables (random syllables get stretched out)
• Monopitch (pitch of voice does not change much)
• Reduced Stress, so you’re not sure what the most important parts of a sentence are
• Monoloudness (unchanged volume), and reduced loudness
• Intermittent breathy segments
• Inappropriate silences
• Short rushes of speech
• Variable rate of speech , but overall increased overall rate
• Palilalia – repeating sounds or words
• Echolalia – repeating other people’s sounds or words

Ataxic – hard to get sounds out due to the effort of coordinating the entire speech process 

• Slow rate
• Everything sounds stressed (not like the psychological stress, but in terms of using prosody to show importance in a sentence)
• Articulation of speech sounds breaks down randomly and inconsistently
• Vowels are particularly off
• Too much volume variation
• Teloscoping of syllables (random syllables get stretched out) and phonemes (specific sounds)

Hyperkinetic – usually due to Basal Ganglia damage, so there’s an excess of movement (common in Huntington’s, Dystonia, and others)

• Can hear inhales and exhales, often very sharply and suddenly
• Usually speak in short phrases
• Harshness vocal quality
• Low pitch
• Slow rate
• Vowels distorted
• Too much variation in volume
• Monopitch (pitch of voice does not change much)
• Variable rate of speech
• Prolonged pauses
• Tremor in voice
• Sometimes hypernasal
• Harder to understand the faster they talk
• Odd vocal noises
• Echolalia (repeating words and sentences from other people)
• Coprolalia (cursing)
• Coming and going of strained voice and breathy voice
• Articulation of speech sounds breaks down randomly and inconsistently

Apraxia of speech is due to difficulty coordinating speech sounds. The hallmarks of apraxia are that error patterns are irregular, meaning that one time someone might substitute a “p” for an “m”, but the next time they might get it right, and then the next time they might substitute “d” for “p”. Words that have more syllables and speaking in sentences may be especially hard for someone with Apraxia of Speech. Speech may sound slurred as well, and as we mentioned above, prosody is usually fairly robotic sounding. This actually takes away a key method that we use to convey information, as prosody helps us to know what the most important parts of a thought are.

There is treatment for speech disorders

The most important tip is often to slow down and carefully articulate each sound in each word. Although this does not fix all issues, it fixes many. Treatment approaches vary depending on which type of dysarthria you might have, or if you have Apraxia. Know, though, that with good therapy and time, these speech disorders can often improve significantly.