What is the recommended dose and muscle injection sites of Botulinum toxin (Botox, onabotulinumtoxinA) for a patient with cervical anterocollis due to dystonia?

Botulinum Toxin Injection for Cervical Anterocollis

For cervical anterocollis due to dystonia, inject botulinum toxin into the deep cervical flexors (longus colli and longus capiti), sternocleidomastoid (SCM), and suprahyoid muscles, with typical starting doses of 75-100 units per muscle group, guided by EMG and/or ultrasound or fluoroscopy. 1, 2

Target Muscles for Anterocollis

The muscle selection depends on the specific anterocollis phenotype:

Primary Target: Deep Cervical Flexors

• Longus colli is the critical deep cervical flexor that must be injected for anterocollis, as superficial muscle injections alone frequently fail 3, 2
• Longus capiti should be targeted when the primary posture involves head flexion rather than pure neck flexion 1
• These deep muscles require image guidance (ultrasound, fluoroscopy, or CT) combined with EMG for safe access 3, 2

Secondary Targets

• Sternocleidomastoid (SCM): Inject the lower portion bilaterally rather than upper portion, as this approach provides better symptom control with fewer dysphagia complications 4
• Suprahyoid muscles: Required in most anterocollis cases, particularly when Meige syndrome or more widespread dystonia is present 1
• Anterior scalene muscles: Consider as adjunctive targets, though often show minimal EMG activity in pure anterocollis 2

Dosing Recommendations

Starting Doses

• Longus colli: 75 units per side bilaterally (total 150 units) 2, 5
• SCM (lower portion): 50-75 units per side bilaterally 4, 5
• Suprahyoid muscles: Dose varies based on involvement, typically 20-40 units total 1

Dose Adjustments

• Posterior neck muscles may require higher doses than anterior muscles for equivalent effect 5
• Increase doses cautiously if initial response is inadequate, as dysphagia risk increases with higher total doses 2, 4
• Treatment intervals typically range from 3-6 months 6

Injection Technique

Guidance Methods

• Combined ultrasound and EMG guidance is the preferred approach for longus colli injection, providing excellent visualization with minimal complications 3
• Fluoroscopic guidance with EMG is an alternative validated technique 2
• Nasal endoscopic approach can be used for longus capiti injection in specialized Neuro-ENT clinics 1

EMG Guidance Principles

• Target muscles showing >100 turns/second at rest on quantitative EMG analysis 5
• EMG confirms proper needle placement and identifies hyperactive muscles objectively 5
• Successful treatment correlates with reduced turns/second and mean amplitude at rest post-injection 5

Clinical Considerations

Common Pitfalls

• Incomplete muscle selection is the primary cause of treatment failure in anterocollis—do not limit injections to SCM and scalenes alone 2
• Upper SCM injection is less effective than lower SCM injection and causes more dysphagia 4
• Inadequate deep flexor targeting leads to the disproportionate treatment failure rate seen in anterocollis compared to other cervical dystonia patterns 2

Side Effects

• Dysphagia is the most common complication, occurring more frequently with dose escalation 2, 4
• Dysphagia is typically mild and transient when proper technique and dosing are used 3, 2
• No serious complications have been reported with ultrasound-guided longus colli injection 3

Expected Outcomes

• Clinical success rates of 89% are achievable with comprehensive muscle targeting 5
• 50% of properly treated patients achieve ≥90% satisfaction 1
• Dramatic improvement occurs when all dystonic muscles (deep cervical flexors, SCM, and suprahyoid) are addressed in the same session 1

Formulation Selection

Use abobotulinumtoxinA (Dysport) or rimabotulinumtoxinB (Myobloc) as first-line agents, as these have the strongest evidence for cervical dystonia efficacy. 7, 8

• OnabotulinumtoxinA (Botox) and incobotulinumtoxinA (Xeomin) are acceptable alternatives with similar efficacy 7, 8
• All FDA-approved formulations demonstrate safety even with decades of repeated use 8

Adjunctive Management

• Refer to rehabilitation specialists for comprehensive neuromusculoskeletal management 6, 7, 8
• Prescribe nerve-stabilizing agents (pregabalin, gabapentin, or duloxetine) for pain management and spasm control, which may also facilitate physical therapy 6, 7, 8