What are the causes of tics?

Causes of Tics

Tics are primarily caused by neurobiological factors including genetic predisposition, neurotransmitter dysregulation, and alterations in cortical-basal ganglia-thalamocortical circuits, with environmental triggers often exacerbating symptoms. 1, 2, 3

Primary Causes

Neurobiological Factors

• Genetic factors: Tourette syndrome and other tic disorders have a strong genetic background, likely involving multiple genes with both low and high-effect variants 3
• Neurotransmitter dysregulation: Dopaminergic system dysfunction is implicated in tic disorders, as evidenced by the effectiveness of dopamine receptor-blocking medications 1, 2
• Brain circuitry abnormalities: Involvement of the cortical-basal ganglia-thalamocortical circuits, with structural and functional neuroimaging showing basal ganglia involvement 3, 4
• Neuroanatomical changes: Evidence shows amygdala overactivity, hippocampus underactivity, and altered prefrontal cortex function 1

Types of Tic Disorders

1. Transient tic disorder:

   • Common pediatric condition (4-24% of elementary school children)
   • Usually self-limited and lasts less than 1 year 1

2. Chronic motor or vocal tic disorder:

   • Lasts more than 1 year
   • Involves either motor or vocal tics, but not both 1

3. Tourette syndrome:

   • Biological, genetic disorder with prevalence of 5-30 per 10,000 children
   • More common in males (1:1,000) than females (1:10,000)
   • Characterized by multiple motor and at least one vocal tic
   • Often presents with neurobehavioral manifestations 1, 2

Secondary Causes

Medical Conditions

• Neurological disorders (9% of cases):

  • Head trauma (2.5%)
  • Stroke (1.2%)
  • Encephalitis (1.9%)
  • Seizure disorders (1.9%)
  • Static encephalopathy (1.2%) 5

• Genetic and chromosomal disorders (10.3% of cases):

  • Down's syndrome (3.2%)
  • Neuroacanthocytosis (1.2%)
  • Huntington's disease (0.6%) 5

• Developmental disorders (13.5% of cases):

  • Asperger's syndrome (8.3%)
  • Mental retardation (2.5%)
  • Autism (1.9%)
  • Savant's syndrome (0.6%) 5

Medication-Induced Tics

• Antipsychotics: Can cause tardive syndromes including tardive tics after chronic exposure 6
• Psychostimulants: Methylphenidate has been associated with tics, though recent evidence suggests it may not exacerbate and may even improve tics in some patients 6
• Antiepileptic drugs: Carbamazepine and lamotrigine have been reported to induce tics 6

Environmental Factors

• Psychological stress: Can trigger or worsen tics 1, 4
• Fatigue: Common exacerbating factor 1
• High altitude: Associated with increased cough tics 1
• Trauma exposure: Can contribute to neurobiological changes that may manifest as tics 1

Common Comorbidities

Tic disorders frequently present with comorbid conditions that can sometimes be more problematic than the tics themselves:

• Attention deficit hyperactivity disorder (ADHD): Present in 50-75% of patients with Tourette syndrome 1, 2
• Obsessive-compulsive disorder (OCD): Present in 30-60% of patients 1, 2
• Anxiety disorders
• Mood disorders
• Sleep disorders 3, 7

Differential Diagnosis

Several conditions may present with movements that resemble tics:

• Psychogenic movement disorders: Distinguished by distractibility, variability, suggestibility, and atypical response to medications 1
• Hyperekplexia: Characterized by excessive startle response to unexpected stimuli, present from birth 1
• Sandifer syndrome: Secondary to gastroesophageal reflux, presenting as paroxysms of head tilt after eating 1
• Benign paroxysmal torticollis: Recurrent episodes of abnormal head postures in infants 1
• Transient dystonia of infancy: Paroxysmal episodes of abnormal upper limb posture 1

Clinical Pearls

• Tics are sudden, brief, intermittent, involuntary or semi-voluntary movements (motor tics) or sounds (phonic/vocal tics) 1
• Phonic tics can include coughing, throat clearing, sniffing, grunting, and other vocalizations 1
• The ability to temporarily suppress tics helps differentiate them from other movement disorders like chorea and dystonia 1
• Tics typically begin in childhood but can occasionally present for the first time in adulthood 1, 5
• The waxing and waning nature of tics is characteristic and should be considered when evaluating treatment response 2, 3

Understanding the multifactorial etiology of tics is essential for proper diagnosis and management, particularly given the high prevalence of comorbid conditions that may require separate treatment approaches.