Difference Between Flaccid and Spastic Dysarthria

Flaccid and spastic dysarthria are distinct types of motor speech disorders characterized by different underlying neurologic mechanisms and clinical features.. While flaccid dysarthria results from lower motor neuron damage and manifests with weakness and reduced tone, spastic dysarthria appears from upper motor neuron lesions and presents with spasticity and effortful speech.

Comparison of Flaccid and Spastic Dysarthria

Feature Flaccid Dysarthria Spastic Dysarthria
Speech Characteristics Articulatory imprecision, breathiness, hypernasality, reduced loudness Slow, effortful speech, strained-strangled voice quality, reduced range
Underlying Cause Damage to lower motor neurons or peripheral nerves Damage to upper motor neurons within corticobulbar tracts
Associated Conditions Guillain-Barré syndrome, polio, myasthenia gravis, motor neuron disease Stroke, traumatic brain injury, multiple sclerosis, cerebral palsy
Assessment Findings Weakness, atrophy, fasciculations in relevant muscles Spasticity, weakness, hyperreflexia in relevant muscles
Treatment Approach Compensation techniques, speech therapy focusing on breath support and clarity Intensive speech therapy, oral medications for spasticity management

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What is Flaccid Dysarthria?

Flaccid Dysarthria is also known as perpheral dysarthria is a condition that causes damage to speech functions. 


Flaccid dysarthria is caused due to the damage to the Peripheral Nervous system (PNS) , especially the lower motor neurons or their fibers, which originate in the brainstem or spinal cord.These neurons are responsible for transmitting signals from the brainstem or spinal cord to the muscles involved in speech production

Common causes includes

  • Guillain-Barre Syndrome (GBS): This autoimmune disorder due to inflammation and damage to the myelin sheath of peripheral nerves. 
  • Polio (Poliovirus Infection): Polio can cause permanent damage to lower motor neurons, leading to muscle weakness and paralysis, including in the muscles used for speech.
  • Myasthenia Gravis: This autoimmune disorder affects neuromuscular transmission, where antibodies attack acetylcholine receptors at the neuromuscular junction. It results in fluctuating muscle weakness, including the muscles used for speech.
  • Motor Neuron Diseases (e.g., ALS): Amyotrophic lateral sclerosis (ALS) and other motor neuron diseases affect both upper and lower motor neurons, leading to progressive muscle weakness and eventual paralysis, including in the muscles involved in speech production.


  • Imprecise Articulation: Speech sounds unclear and may involve difficulty in forming sounds precisely, leading to slurred speech.
  • Breathiness: Voice quality often lacks the usual fullness and clarity resulting in a breathy or airy sound.
  • Hypernasality: Excessive nasal resonance occurs during speech.
  • Reduced Loudness: Speech volume is typically lower than normal due to weakened muscles Weakness and Atrophy: Muscles involved in speech production, such as those in the face, tongue, lips, and throat, may show signs of weakness.
  • Difficulty Controlling Pitch and Intonation: Patients may have trouble modulating their pitch (tone of voice) and intonation (rhythm and melody of speech), leading to a monotone or unnatural speech pattern.

Treatment Methods

  • Speech Therapy: Focuses on strengthening muscles for improved articulation and breath support.
  • Compensatory Techniques: Teaching strategies to enhance speech clarity and volume.
  • Exercises: Targeting facial, tongue, and throat muscles to improve coordination and strength.
  • Augmentative and Alternative Communication (AAC): Devices or techniques to supplement verbal communication if needed.
  • Medical Management: Addressing underlying conditions causing dysarthria, such as managing myasthenia gravis or optimizing neuromuscular function.
  • Multidisciplinary Approach: Involving neurologists, speech-language pathologists, and physiotherapists for comprehensive care.



What is Spastic Dysarthria?

Spastic dysarthria is a motor speech disorder that results from damage to the upper motor neurons in the central nervous system.. It's also known as upper motor neuron or pseudobulbar dysarthria.


  • Stroke
  • Traumatic Brain Injury (TBI)
  • Multiple Sclerosis (MS)
  • Cerebral Palsy
  • Brain Tumors or Lesions


  • Slow, Effortful Speech: Speech production is slow due to increased muscle tone and stiffness.
  • Strained-Strangled Voice Quality: Voice sounds tight and forced due to hyperadduction of the vocal folds.
  • Imprecise Articulation: Difficulty in clearly pronouncing sounds and words, leading to slurred speech.
  • Monotone Pitch: Limited pitch variation, resulting in flat speech.
  • Reduced Speech Rate: Slow speech rate with prolonged sounds and syllables.
  • Hypernasality: Excessive nasal resonance in speech due to velopharyngeal dysfunction.
  • Emotional Lability: Inappropriate laughing or crying due to pseudobulbar affect, a common feature in upper motor neuron disorders.
  • Spasticity in Facial Muscles: Increased muscle tone and stiffness in the facial muscles affecting expressions.


  • Speech Therapy: Techniques to improve articulation, resonance, and prosody.
  • Relaxation Exercises: Strategies to reduce muscle tension and spasticity in speech muscles.
  • Breathing Exercises: Enhancing breath support for better speech production.
  • Voice Therapy: Addressing strained-strangled voice quality and promoting a more natural vocal tone.
  • Medications: Antispasticity drugs to reduce muscle stiffness and improve speech.
  • Assistive Devices: AAC tools to supplement verbal communication if necessary.

Difference and similarity between spastic and Flaccid Dysarthria


  • Spastic Dysarthria: Characterized by slow, effortful speech, strained-strangled voice quality, and muscle spasticity.
  • Flaccid Dysarthria: Features breathy, hypernasal speech, reduced loudness, and muscle weakness.


  • Both involve impaired speech production due to neurological damage.
  • Both require speech therapy and multidisciplinary approaches for management.

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What is flaccid dysarthria?

Flaccid dysarthria is a motor speech disorder caused by damage to the lower motor neurons, leading to muscle weakness and atrophy in the speech production muscles.

What causes flaccid dysarthria?

Common causes include Guillain-Barré syndrome, polio, myasthenia gravis, motor neuron disease (e.g., ALS), and trauma or injury to the lower motor neurons.

What is spastic dysarthria?

Spastic dysarthria is a motor speech disorder caused by damage to the upper motor neurons, resulting in muscle spasticity and increased tone in the speech production muscles.

What causes spastic dysarthria?

Causes include stroke, traumatic brain injury, multiple sclerosis, cerebral palsy, brain tumors, and certain neurodegenerative diseases.

What are the treatment options for spastic dysarthria?

Treatment includes speech therapy focusing on relaxation techniques, breath support, voice modulation, medications for muscle spasticity, and AAC tools if needed.