Dysarthria is a speech articulation impairment affecting intelligibility, particularly through consonant production. It can also disrupt phonation, resonation, and prosody, leading to slurred, effortful speech. Dysarthria is often associated with dysphagia, necessitating careful evaluation of airway protection.

Pathophysiology

• Neuromuscular Disorder: Dysarthria reflects a severe impairment of the neuromuscular control of speech.
• Neural Pathway Involvement:
  • Bilateral lesions of neural pathways (corticobulbar and spinal tracts).
  • Affected structures include:
    • White Matter: Corticobulbar tracts, corona radiata, central semiovale, internal capsule.
    • Gray Matter: Persylvian and perirolandic cortices, basal ganglia (putamen, caudate nucleus), thalamus, cerebellum.
  • Key Predictor: Involvement of the dorsal corticobulbar tract predicts poor outcomes.

Epidemiology

• Cerebral Palsy:
  • Affects ~33% of children with CP.
  • Spastic and hyperkinetic dysarthria types are most common.
  • A quarter of children with CP lack speech entirely, with functional communication correlated with motor functioning 
  • Communication in Cerebral Palsy:
    • The Communication Function Classification System (CFCS) aligns with WHO's ICF to describe functional communication performance.
    • Gross motor functioning predicts communication ability at school entry 
• Traumatic Brain Injury (TBI):
  • Affects ~20% of children surviving moderate to severe TBI.
  • Often accompanied by oromotor deficits, including cranial nerve dysfunction (e.g., facial, hypoglossal, vagus, and trigeminal nerves) 
  • Commonly accompanied by:
    • Oromotor Deficits:
      • Facial nerve: Buccal and labial movement.
      • Hypoglossal nerve: Tongue strength and coordination.
      • Trigeminal nerve: Jaw movements.
      • Vagus nerve: Velopharyngeal function.
    • Dysphagia: Reported in 10% of children with moderate-severe TBI
• Posterior Fossa Tumors:
  • Dysarthria occurs in ~33% of children post-resection 

Types of Dysarthria with Clinical Features and Aetiologies

Flaccid Dysarthria (Lower Motor Neuron Lesion)

• Clinical Features:
  • Lax open mouth
  • Atonia
  • Weakness
  • Wasting
  • Drooling
  • Feeding difficulties
  • Absent jaw, gag, and cough reflex
• Causes:
  • Dystrophia myotonica
  • Prader-Willi Syndrome
  • Myasthenia Gravis
  • Facio-scapulo-humeral dystrophy
  • Congenital dysplasia of the brainstem (e.g., Moebius syndrome)
  • Pontine gliomas
  • Progressive motor neuron disease (e.g., Fazio-Londe syndrome)
  • Vascular lesions of the brainstem
  • Posterior fossa tumor resection

Spastic Dysarthria (Upper Motor Neuron Lesion)

• Clinical Features:
  • Release of brainstem reflexes
  • Stiff jaw
  • Difficulty opening mouth
  • Brisk jaw jerk with clonus
  • Small, bunched tongue
  • Rapid tongue movements difficult
  • Gag and cough reflexes present, no wasting
• Causes:
  • Cerebral Palsy
  • Degenerative brain diseases (e.g., Battens disease, Metachromatic leukodystrophy)
  • Acquired traumatic brain injury

Extrapyramidal Dysarthria (Basal Ganglia Lesion)

• Clinical Features:
  • Many unwanted movements interfering with normal articulation
  • Retention of obligatory feeding reflexes
  • Gag and cough reflex retained
• Causes:
  • Kernicterus
  • Hypoxic-ischemic brain injury
  • Degenerative diseases of the basal ganglia

Ataxic Dysarthria (Cerebellar Lesion)

• Clinical Features:
  • Gag and cough reflex retained
  • Disrupted rhythm and volume control
  • Verbal dyspraxia features
  • Slow development of speech articulation
• Causes:
  • Congenital abnormalities of the cerebellum
  • Posterior fossa resections
  • Syndromic examples (e.g., Joubert syndrome)
  • Post-acquired cerebellar disorders

Infectious Causes

• Herpes Virus Brain Infections
  • Pathophysiology: Predilection for temporal lobes, but may involve opercular regions.
  • Clinical Presentation:
    • Encephalitis with fever, seizures, altered mental status.
    • Rarely presents as Opercular Syndrome:
      • Facial palsy.
      • Dysarthria and dysphasia.
    • May mimic other neurological disorders.
  • Management:
    • High-dose intravenous acyclovir immediately.
    • Recognize opercular syndrome as a potential herpes simplex virus (HSV) infection.

Metabolic Causes

• Association with Metabolic Disorders
  • Rare but reported associations with dysarthria.
  • Examples:
    • Leukodystrophies: White matter impairment.
    • Gangliosidoses: Involvement of cerebellum and basal ganglia.
    • Wilson’s Disease: Copper accumulation affecting basal ganglia.

Basal Ganglia Disorders

1. Juvenile Huntington's Chorea

   • Rare in pediatrics but a recognized cause of dysarthria.
   • Features: Progressive motor dysfunction, chorea, and cognitive decline.

2. Pantothenate Kinase-Associated Neurodegeneration (PKAN)

   • Neurodegeneration with iron accumulation in the brain.
   • Dysarthria due to basal ganglia involvement.
   • Associated with dystonia, rigidity, and gait abnormalities.

Rare Motor Neuron Diseases

1. Brown-Vialetto-Van-Laere Syndrome

   • Etiology: Riboflavin transporter deficiency.
   • Presentation:
     • Onset dysarthria.
     • Progressive sensorineural hearing loss.
     • Weakness in cranial and limb muscles.
   • Treatment: High-dose riboflavin supplementation to slow progression.

2. Fazio-Londe Syndrome

   • Etiology: Autosomal recessive disorder affecting motor neurons.
   • Presentation:
     • Dysarthria as an early symptom.
     • Rapid progression:
       • Stridor.
       • Respiratory distress.
       • Ptosis.
       • Facial and limb weakness.
     • Median progression period: 16–18 months.
   • Investigations:
     • Neurophysiology and electromyography (EMG): Confirms anterior horn cell involvement in cranial nerve nuclei and spinal cord.
   • Management: Riboflavin therapy and supportive care.

White Matter Disorders

1. Leukodystrophies

   • Dysarthria results from diffuse white matter involvement.
   • Examples:
     • Metachromatic leukodystrophy.
     • Adrenoleukodystrophy.

2. Gangliosidosis

   • Involves cerebellum and basal ganglia, contributing to dysarthria.

Key Investigations

1. Neuroimaging

   • MRI:
     • Temporal lobe changes in HSV encephalitis.
     • White matter abnormalities in leukodystrophies.
     • Basal ganglia iron deposition in PKAN.

2. Laboratory Tests

   • Serum and CSF: HSV PCR, metabolic workup (e.g., copper studies in Wilson’s disease).
   • Genetic Testing: For PKAN, leukodystrophies, or hereditary motor neuron diseases.

3. Neurophysiology

   • EMG and nerve conduction studies: To identify anterior horn cell involvement in Fazio-Londe syndrome.

Management Overview

• Infectious Causes: Immediate antiviral therapy (e.g., acyclovir for HSV).
• Metabolic Causes: Disease-specific treatments (e.g., chelation for Wilson’s disease).
• Motor Neuron Diseases: Riboflavin supplementation and multidisciplinary care.
• Symptomatic Management: Speech therapy, nutritional support, and addressing complications.