Dystonia

INDEX

Anatomically, the tongue is divided into two distinct sets of muscles:
- Extrinsic tongue muscles insert into the tongue from outside origins move the whole tongue in different directions,
- Intrinsic tongue muscles insert into the tongue from origins within it and allow the tongue to change its shape (such as curling the tongue in a loop or flattening it).

Abnormal lingual muscle contraction may be classified into four subtypes:

  1. Protrusion
  2. Retraction
  3. Curling: presents as upward curling contraction of the tongue, which may be task-specific.
  4. Laterotrusion: presents as lateral deviation of the tongue1

    Patients with the protrusion type of lingual dystonia may also have laterotrusion or curling.

TREATMENT

Treatment is with botulinum toxin; typically this is for tongue protrusion in which case the posterior fibres of genioglossus require injection.

The muscles of this region include those of the submental complex: geniohyoid, mylohyoid, and the anterior bellly of the digastric.

Figure 1. Submental complex

 

Injection begins by identifying the hyoid bone.  This forms the inferior margin of the submental triangle; the lateral border is made up of the anterior belly of the digastric muscle. The digastric muscle is activated by opening mouth slightly.

The insertion points are two sites 25–30 mm posterior from the midline of the body of the mandible and 15–20 mm apart from each other (Figure 2).

Alternative injection sites include:

  1. Directly to the top of the tongue by an introral approach2.
  2. Injecting deep from the lateral border of the tongue by an intraoral approach (patient sticks out their tongue, which is lightly held with gauze).

 

Figure 2. Injection sites

The needle is placed with EMG guidance through the digastric and mylohyoid muscles, and then into the genioglossus muscle at a depth of approximately 2cm 3.  The patient should close the mouth lightly and push the tongue against the back of the teeth, which will activate the muscle, which can be easily felt.

 

Figure 3. Needle passing through anterior body of the digastric muscle

 

From: Cultrara A, Chitkara A, Blitzer A. Botulinum toxin injections for the treatment of oromandibular dystonia. Oper Tech Otolaryngol - Head Neck Surg 2004; 15: 97–102

 

Figure 4. Muscles through which needle passes in order to reach genioglossus muscle

 

Dose for lingual injections

Use a low dose, high concentration of toxin; 10-12.5 per side.
The therapeutic window is narrow and therefore it is recommended to commence with a starting dose of 5 units in each genioglossus muscle.  This may be increased by 2.5 units in each successive treatment until the patients achieves a reasonable response.

 

 

 

 

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References

  1. Yoshida K. Botulinum neurotoxin therapy for lingual dystonia using an individualized injection method based on clinical features. Toxins (Basel) 2019; 11: 1–18.
  2. Kasravi N, Jog MS. Botulinum toxin in the treatment of lingual movement disorders. Mov Disord. 2009 Nov 15;24(15):2199-202. doi: 10.1002/mds.22549. PMID: 19795478.
  3. Odell K, Sinha U. Dystonia of the Oromandibular, Lingual and Laryngeal Areas. In: Rosale, ed. Dystonia - The Many Facets. 2012. DOI:10.5772/28356.