Touching the chin can briefly switch off some dystonia spasms
Dystonia makes muscles contract on their own, twisting the body into repetitive movements or fixed, abnormal postures. One of its oddest features is the sensory trick: a simple gesture, such as touching the chin, can temporarily interrupt the spasms. Even where the disorder starts in the brain is under debate.
The involuntary contractions can resemble a tremor, tend to worsen with physical activity and may spread to neighbouring muscles. Many people live with constant pain, cramping and spasms. Causes include inherited genes, birth injury or other trauma, infections such as meningitis and encephalitis, lead poisoning, stress and reactions to medicines, especially neuroleptics. Genes linked to it include GNAL, PRRT2 and THAP1.
A 2013 consensus update sorts dystonia chiefly as isolated, when it is the only neurological sign, or combined, when it appears alongside features like parkinsonism. It is also classed by age of onset, the body parts affected and cause. Eyelid spasms paired with jaw and mouth involvement are called Meige's syndrome. Service-based counts come out lower, but careful population studies put adult-onset focal dystonia as high as 732 per 100,000 people.
Diagnosis is tricky, and patients may first be labelled with Parkinson's disease, essential tremor, carpal tunnel syndrome or Tourette's. One man in a recent case report carried a cerebral palsy diagnosis for 40 years before genetic sequencing tied his generalised dystonia to a new variant. The basal ganglia were traditionally blamed, but newer evidence implicates the cerebellum too, and faults in the sodium-potassium pump that sets the activity of cerebellar Purkinje neurons may matter in some forms.
Treatment has to be tailored and usually carries side effects: oral drugs, botulinum toxin injections, physical therapy and sometimes surgery that cuts selected nerves. Some hereditary myoclonic cases have responded well to alcohol. Researchers such as Nancy Byl and Joaquin Farias have explored sensorimotor retraining to encourage the brain to rewire, but physiotherapy studies remain small and poorly controlled, and no gold-standard rehabilitation exists.
Source: Dystonia
