In a patient with right‑sided cervical dystonia (torticollis), which neck muscles should be injected with onabotulinum toxin A (Botox) and what dose should be given to each muscle?

Botulinum Toxin Injection for Right-Sided Cervical Dystonia

For right-sided torticollis, inject the right sternocleidomastoid (SCM) and right splenius capitis muscles as primary targets, using 40-60 units of onabotulinumtoxinA (Botox) per muscle, with total doses typically ranging 150-200 units distributed across involved muscles based on the specific dystonic pattern. 1

Understanding the Dystonic Pattern

Right-sided torticollis typically involves rotation of the head to the left (chin pointing left) with the right side muscles being hyperactive. The specific muscles to target depend on the exact head posture:

• For pure rotational torticollis (head turned left): The right SCM and right splenius capitis are the primary targets, as these muscles rotate the head to the opposite side when contracted 2
• If lateral tilt is present (right ear toward right shoulder): Add the right scalene muscles and right levator scapulae 2
• If shoulder elevation occurs: Include the right trapezius muscle 2

Recommended Injection Protocol

Primary Muscle Targets and Doses (OnabotulinumtoxinA/Botox):

• Right Sternocleidomastoid (SCM): 40-60 units

  • This muscle is consistently involved in rotational torticollis 3, 4
  • Doses between 200-400 mouse units (approximately 40-80 units of commercial Botox) per muscle are optimal 4

• Right Splenius Capitis: 50-80 units

  • Mean effective doses reported as 61.3 ± 5.16 units of Botox 3
  • This posterior neck muscle is a key rotator and commonly dystonic 3

Secondary Muscle Targets (if clinically indicated):

• Right Levator Scapulae: 30-50 units if shoulder elevation present 2
• Right Trapezius (upper fibers): 30-50 units if shoulder elevation present 2
• Right Scalene muscles: 20-40 units if lateral tilt component exists 2

Total Dosing Considerations

• Total dose per session: Typically 150-200 units of onabotulinumtoxinA, though can range up to 300 units depending on severity and muscle involvement 5, 6
• Treatment interval: Every 12-16 weeks, with effect onset at approximately 9-10 days and duration of 15-16 weeks 3, 5

Critical Technical Points

Muscle identification is crucial for treatment success. While clinical evaluation alone can guide injection, polymyographic electromyography (EMG) guidance may improve outcomes by revealing different patterns of muscle involvement than clinical examination alone 7. EMG guidance ensures accurate needle placement in the target muscles 7.

Common pitfalls to avoid:

• Dysphagia risk: Occurs in approximately 10-22% of treatments, particularly with SCM injections 4, 5. Use lower SCM doses (40-50 units) initially to minimize this risk
• Neck weakness: Reported in 10% of sessions, usually transient 4. Avoid over-dosing posterior neck muscles
• Underdosing: Doses below 200 mouse units per muscle are often suboptimal 4

Evidence Quality

The American Academy of Neurology guidelines establish that onabotulinumtoxinA should be considered for cervical dystonia treatment with demonstrated efficacy 1. Long-term safety data spanning 25 years confirms sustained efficacy with mean global clinical improvement scores of 4±1 and side effects in only 9% of treatments 5. The specific dosing recommendations derive from multiple prospective studies showing 70-86% improvement rates with these dose ranges 3, 2.

The pattern-based approach to muscle selection (identifying rotation, tilt, and shoulder elevation components) improves treatment outcomes compared to empiric injection 2. Consider using the COL-CAP phenomenological classification system to systematically identify all dystonic muscles 8.