Dystonias are characterized by involuntary muscle contractions, twisting
movements, abnormal postures, and often
tremor in various body regions. However, in the last decade several studies have demonstrated that dystonias are also characterized by sensory abnormalities. While
botulinum toxin is the gold standard
therapy for
focal dystonia, exactly how it improves this disorder is not entirely understood. Neurophysiological studies in animals and humans have clearly demonstrated that
botulinum toxin improves dystonic motor manifestations by inducing
chemodenervation, therefore weakening the injected muscles. In addition, neurophysiological and neuroimaging evidence also suggests that
botulinum toxin modulates the activity of various neural structures in the CNS distant from the injected site, particularly cortical motor and sensory areas. Concordantly, recent studies have shown that in patients with
focal dystonias botulinum toxin ameliorates sensory disturbances, including reduced spatial discrimination acuity and
pain. Overall, these observations suggest that in these patients
botulinum toxin-induced effects encompass complex mechanisms beyond
chemodenervation of the injected muscles.