Dystonia

INDEX

 

Blepharospasm is a dystonia of the facial musculature that ranges in severity from an increased blink rate to disabling contractions with pain and visual dysfunction. Blepharospasm is characterized by excessive contraction of the orbicularis oculi muscles, and patients often may attempt eyebrow elevation to overcome the problem.

Diagnosis is based on clinical recognition.
Exacerbating and alleviating factors, the presence of sensory tricks, and dystonia elsewhere should be evaluated.
Brain imaging is rarely needed; blood tests are unrevealing.

Differential diagnosis:

Figure 1. Basic terms of the components of orbicularis oculi

Anatomy

The orbicularis oculi muscle lies in a plane just deep to the subcutaneous tissue; the skin of the eyelids is the thinnest skin in the body and contains very little subcutaneous fat. Thus, the orbicularis oculi muscle may lie just 1 mm below the surface of the skin. The muscle is divided into orbital and palpebral parts:

- Orbital portion forms a wide circle around the orbital rims and interdigitates with other facial muscles. It is under voluntary control and is responsible for tight closure of the eyelids.
- Palpebral part involuntarily and gently closes the eye during blinking and sleep and is further divided into:

Figure 2. Potential preseptal and pretarsal injection sites

From: Truong D, Dressler D, Hallett M, Zachary C, editors. Manual of Botulinum Toxin Therapy [Internet]. Cambridge University Press; 2014

Treatment

Artificial tears are recommended for eye dryness, but do not improve spasm.
Surgical myotomy or myectomy produces relief in over 80% of patients, but symptoms may recur. Surgery may also incur complications including bruising, numbness, eyebrow/eyelash loss, and skin loss requiring grafting and disfiguration; therefore, it is largely reserved for patients with severe symptoms that are not controlled with toxin injections.

It is recommended to avoid injection of botulinum toxin in the following sites:

Commonly a combination of the pretarsal and preseptal injections is useful;  pretarsal injections may have a longer duration of benefit and fewer side effects, such as ptosis. However, preseptal and/or orbital injections can be included if those areas appear especially active.

Dose: typically 2-2.5 units Botulinum: total of 5 injections per eye (12. 5 u); total 25 units for both eyes.
A survey of oculoplastic surgeons found a mean starting dose of 22.5   9.5 U onaBoNT-A per eye.35 The mean maximal dose to induce a stable response among their patients was 50 U per eye

Common side effects include ptosis, entropion, bruising, tearing, dry eyes, lagophthalmos, keratitis, and diplopia. All are rarely severe and are reversible. Longitudinal studies have shown no worsening or other adverse effects with repeated use over more than 20 years.

Figure 3. Commonly used approach, combining pretarsal and preseptal sites.

 

 

 

 

 

References