SYDNEY—A new guideline defines dystonia as a movement disorder and classifies it along the twin axes of clinical characteristics and etiology. According to the new guideline from the Movement Disorder Society, dystonia is “characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both.
“Dystonic movements are typically patterned and twisting and may be tremulous. Dystonia is often initiated or worsened by voluntary action and associated with overflow muscle activation,” the guideline states.
The guideline, presented at the 17th International Congress of Parkinson’s Disease and Movement Disorders, also describes a new approach to classifying dystonias according to their phenomenologic appearance and etiology.
Mark Hallett, MD, a member of the guideline review committee, said that this change resulted because of the difficulties in trying to classify individual patients according to a system that assumed a one-to-one match between a particular phenotype and a specific disease entity or cause.
“The problem is that we have patients who have certain characteristics, and there can be many possible causes,” said Dr. Hallett, Chief of the Human Motor Control Section of NINDS in Bethesda, Maryland. “On the other hand, we have individual causes such as individual genetic abnormalities that can have many different phenotypes, many different clinical syndromes associated with them.
“We now have a two-axis approach to the classification of different disorders,” Dr. Hallett explained. “One axis is the phenomenologic appearance, and the other is the etiology, so any individual case would be described as one phenotype and one or more etiologies.”
The first axis of clinical characteristics incorporates information such as age at onset, body distribution, and temporal pattern, while the second axis of etiology examines nervous system pathology and whether the dystonia is inherited, acquired, or idiopathic. The guideline also moves away from phenotypic classifications of “primary” and “secondary” dystonia toward the terminology of “isolated” and “combined” dystonia.
In isolated dystonia, dystonia is the only motor feature. Combined dystonia refers to dystonia combined with other movement disorders such as myoclonus or Parkinsonism.
—Bianca Nogrady
IMNG Medical News