What is muscle tension?

Muscle tone refers to the force generated by the mutual traction between muscle cells. In daily life, our muscle tone can be coordinated and controlled by the brain. However, if there is a structural abnormality in the brain or abnormalities caused by other reasons, this control power will often decrease, leading to excessive muscle tone. This situation often occurs in some infants and young children, such as patients with cerebral palsy, Down syndrome, etc.

Causes and mechanisms

Decreased muscle tone may occur in various myopathies, myasthenia gravis, peripheral neuropathy, radiculitis or cerebellar damage. Blockage of the nerve fibers that transmit proprioception in the spinal cord can also cause a decrease in muscle tone. In children with acute hemiplegia, they may have low muscle tone in the early stages of paralysis, and then increased muscle tone and enhanced tendon reflexes may occur after a few days or weeks.

Paroxysmal or intermittent hypotonia may occur in familial periodic paralysis, stenoses, and atonic seizures of epilepsy. Pyramidal system diseases cause increased muscle tone. The muscle tone of extrapyramidal system and basal ganglia lesions may be reduced or increased, sometimes manifesting as increased gear-like muscle tone. In decerebrate rigidity, muscle tone increases significantly, the limbs are rigid, the lower limbs are extended, the upper limbs are flexed, and the head is tilted back.

Definition of Dystonia

In 1984, the Advisory Committee of the International Dystonia Medical Research Foundation (DMRF) proposed a definition of dystonia: dystonia is a syndrome of twisting, repetitive movements or abnormal postures caused by involuntary, sustained muscle contractions. This definition is still widely used as the classic description of dystonia.

However, this definition focuses mainly on "sustained muscle contractions" and excludes muscle contractions of shorter duration; the specific characteristics of dystonia, such as the patterning and stereotypy of movements, movement induction and generalization phenomena, are not clearly described.

Therefore, in 2013, Albanese et al. proposed a new definition of dystonia: dystonia is a movement disorder characterized by abnormal (mostly repetitive) movements and/or postures caused by sustained or intermittent muscle contractions, which can be induced or aggravated by voluntary movements [related to overflow], and the abnormal movements are mainly manifested as patterned, torsional and tremorous movements. This new definition combines abnormal movements with abnormal postures and retains the characteristic phenotype of abnormal movements, helping to differentiate them from pseudodystonia.