What is writer's cramp (focal dystonia) and how is it managed?

Writer's Cramp: A Focal Dystonia and Its Management

Writer's cramp is a focal task-specific dystonia characterized by involuntary muscle contractions that cause abnormal postures or movements during writing, with botulinum toxin injections being the first-line treatment for symptom control.

Definition and Clinical Presentation

Writer's cramp is the most common form of focal task-specific dystonia that affects the hand and upper extremity specifically during writing or holding a writing utensil 1. It manifests as:

• Involuntary muscle contractions causing abnormal postures or movements
• Symptoms that typically develop in the setting of repetitive hand movements and increased writing demands
• Various dystonic patterns of the upper extremity specifically while writing
• Preserved consciousness during dystonic episodes

The condition can be classified into two types:

• Simple writer's cramp: Dystonia occurs only during writing
• Dystonic writer's cramp: Dystonia occurs during writing and may extend to other manual tasks

Pathophysiology

While the exact cause remains unclear, writer's cramp is believed to involve dysfunction in the pallido-thalamo-cortical circuit 2. Recent studies have demonstrated:

• Reduced activation of the primary motor cortex during writing
• Hyperactivity of frontal non-primary motor areas, particularly the premotor cortex
• Deficient cortical inhibition in the motor cortex
• Possible genetic factors in some cases, especially in dystonic writer's cramp 3

Diagnostic Approach

Diagnosis is primarily clinical and should include:

• Detailed clinical evaluation of the dystonic movements during writing tasks
• Assessment of whether symptoms occur only during writing or extend to other manual tasks
• Evaluation for possible secondary causes through appropriate laboratory tests:
  • Thyroid function tests
  • Calcium-phosphorus metabolism
  • Blood glucose test
  • Bilirubin levels
  • Serum ceruloplasmin levels 4
• Brain imaging (MRI/CT) may be necessary in some cases 4
• Genetic testing if there is a family history of dystonia 4

Treatment Options

First-Line Treatment

Botulinum toxin injections into affected muscles are the first-line treatment for writer's cramp, providing symptom control for 3-6 months before requiring repeat injection 4, 5. This approach:

• Has shown improvement in approximately 73% of patients 5
• Works by causing transient, nondestructive flaccid paralysis of muscles by inhibiting acetylcholine release 6
• Requires careful selection of target muscles, which remains an area of active research 5

Second-Line Treatments

If botulinum toxin is ineffective or contraindicated, consider:

1. Oral medications:

   • Anticholinergics (trihexyphenidyl, benztropine) - especially effective in younger patients 4
   • Benzodiazepines (clonazepam, diazepam) - particularly useful when dystonia is associated with anxiety or pain 4
   • Baclofen - most effective for dystonia with associated spasticity 4

2. Rehabilitation approaches 6:

   • Encouraging optimal postural alignment during writing
   • Graded activity to normalize movement patterns
   • Avoiding postures that promote prolonged positioning of joints at end range
   • Strategies to reduce muscle overactivity, pain, and fatigue

3. Advanced interventions for refractory cases:

   • Stereotactic ventrooralis thalamotomy - has shown immediate postoperative disappearance of dystonic symptoms in selected cases 2
   • Subthreshold low-frequency repetitive transcranial magnetic stimulation (rTMS) over the premotor cortex - has demonstrated improvement in handwriting and prolonged silent period in patients with writer's cramp 7

Treatment Algorithm

1. Initial management:

   • Botulinum toxin injections into affected muscles
   • Reassess every 3-6 months for repeat injections

2. If inadequate response to botulinum toxin:

   • Add oral anticholinergics (trihexyphenidyl or benztropine)
   • Consider benzodiazepines if anxiety or pain is a component
   • Implement rehabilitation strategies focusing on posture and normalized movement patterns

3. For refractory cases:

   • Consider neurosurgical interventions like stereotactic thalamotomy
   • Evaluate for rTMS over the premotor cortex
   • Deep brain stimulation may be considered for medication-refractory cases 4

Follow-up and Monitoring

• Regular follow-up every 3-6 months for patients on long-term therapy
• Monitor for side effects and treatment efficacy
• Reassess before each botulinum toxin injection cycle
• Gradual dose titration for oral medications 4

Cautions and Considerations

• Splinting may prevent restoration of normal movement and function and could potentially worsen symptoms 6
• Potential problems with splinting include:
  • Increased attention and focus to the affected area
  • Increased accessory muscle use
  • Use of compensatory movement strategies
  • Muscle deconditioning from immobilization
  • Learnt non-use
  • Increased pain 6

By following this structured approach to diagnosis and treatment, most patients with writer's cramp can achieve significant symptom improvement and maintain their writing ability and quality of life.