What is the function of the nasalis muscle and how do neuromodulators like Botox (Botulinum Toxin) affect it?

Function and Effect of Botulinum Toxin on the Nasalis Muscle

Botulinum toxin injections into the nasalis muscle effectively reduce muscle activity by blocking acetylcholine release at neuromuscular junctions, resulting in temporary paralysis that can improve both functional nasal breathing and aesthetic appearance.

Anatomy and Function of the Nasalis Muscle

The nasalis muscle consists of two parts that work together to regulate nasal airway patency:

1. Transverse part (compressor naris): Compresses the nasal aperture
2. Alar part (dilator naris): Widens the nostrils during inspiration

The nasalis muscle plays several important roles:

• Maintains structural tension in the nasal airway at rest 1
• Actively dilates the nostrils during increased respiratory demand 2
• Prevents collapse of the nasal valve during inspiration 2
• Contributes to facial expressions 2

Mechanism of Botulinum Toxin Action

When injected into the nasalis muscle, botulinum toxin:

1. Binds to acceptor sites on motor nerve terminals
2. Enters the nerve terminals
3. Cleaves SNAP-25 protein, inhibiting acetylcholine release
4. Produces localized chemical denervation of the muscle
5. Reduces muscle activity and may cause temporary muscle atrophy 3

The effects are temporary, with reinnervation of the muscle occurring over time as new nerve terminals sprout 3.

Clinical Applications of Botulinum Toxin in the Nasalis Muscle

1. Functional Applications

• Treatment of nasal obstruction: Targeted injections into the supra-alar nasalis and depressor septi muscles can significantly improve nasal obstruction symptoms in patients with facial synkinesis 4
• Improvement in NOSE scores: Studies show significant reduction in Nasal Obstruction Symptom Evaluation scores following botulinum toxin treatment 4

2. Aesthetic Applications

• Reduction in nasal tip drooping: Botulinum toxin can improve the appearance of the nasal tip 5
• Softening of nasal flare: Reduces excessive nostril flaring during facial expressions 5
• Improvement in overall facial expression: When treated as part of a global facial approach 5

Injection Technique

For optimal results when injecting the nasalis muscle:

• Dosage: Typically 2-2.5 units per side 4
• Target locations:
  • Supra-alar nasalis
  • Depressor septi muscles
• Approach: Injections should be precise to avoid affecting adjacent muscles

Potential Side Effects and Considerations

• Temporary muscle weakness: Expected effect that resolves as the toxin wears off
• Risk of nasal valve collapse: Excessive paralysis could potentially compromise the nasal airway in some patients
• Contraindications: Allergy to botulinum toxin, infection at injection site, neuromuscular junction disorders like myasthenia gravis 6

Clinical Outcomes

• Approximately 74% of patients with synkinesis-related nasal obstruction experience symptom relief following botulinum toxin treatment 4
• Effects typically last 3-4 months, requiring repeat injections for sustained benefit
• Patient satisfaction is generally high when appropriate dosing and technique are used

Conclusion

Botulinum toxin injections provide an effective, minimally invasive approach for addressing both functional and aesthetic concerns related to the nasalis muscle. The treatment works by temporarily paralyzing the muscle through inhibition of acetylcholine release, with effects lasting several months before gradual recovery occurs through nerve terminal sprouting.