Craniofacial Muscles

16 Spastic Facial Muscle Disorders
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or 300 units of Dysport ® per session; an interval of less than 3 months between
two injections; using the “Booster” technique where another dose is injected
2–3 weeks after the fi rst injection; and use of a BoNT drug with a low intrinsic
activity. Cumulative dose, treatment time, and patient age have been excluded
as risk factors. Antibody-induced therapy failure usually develops within the
fi rst 2–3 years of BoNT therapy (Dressler 2002 ).
The intrinsic activity of BoNT drugs is de fi ned as the number of toxin units
per amount (nanograms) of clostridial proteins (i.e., toxin complex). At each
injection of toxin, the administered protein mass will be greater when using a
toxin with a low intrinsic activity. The toxin’s antigenic potential is probably
related to the total protein concentration injected (protein load). This may be a
much more relevant parameter in the development of resistance than the number
of units injected (Borodic et al. 1996 ). In patients with cervical dystonia, the
original formulation of Botox ® (100 units/25 ng protein) was six times more
likely to elicit the production of neutralizing antibodies than the newer formulation
of Botox ® (100 units/5 ng protein). The authors conclude that the low risk
of antibody formation after newer Botox ® treatment is related to lower protein
load (Jankovic et al. 2003 ).
The newly FDA approved BoNT/A drug Xeomin ® may reduce antibodyinduced
therapy failure, since it contains only the pure neurotoxin (150 kDa)
produced by a manufacturing process that separates it from complexing proteins
such as hemagglutinins and other proteins in the neurotoxin complex
(Frevert 2009 ; Park et al. 2011 ). Long-term comparative trials in naïve patients
between Xeomin ® and conventional BoNT/A drugs are required to con fi rm the
lower immunogenicity of Xeomin ® (Park et al. 2011 ).
(f) Systemic Toxic Effects : The LD in humans is approximately 390,000 unit/kg,
50
and single injection of more than 500 units may cause acute systemic toxicity.
Systemic toxic effects have not been reported in the treatment of cranial dystonia
because the amount for each treatment is relatively small.
(g) Excessive Facial Weakness : In the patients with Meige’s syndrome or hemifacial
spasm, injections in the mid- and lower facial muscles may induce excessive
facial weakness. Careful toxin injection of appropriate drug levels can
reduce this side effect.
16.8.2 Psychotherapy
Psychotherapy such as behavior modi fi cation and biofeedback has been used to
decrease the frequency and amplitude of spasm. The principle is based on teaching
patients to control their muscle contractions using an electromyographic recording.