hypertonia

Hypertonia is an abnormally increased resistance to passive movement of a muscle or muscle group. It is typically the result of abnormalities in the central nervous system that alter the control of muscle activity, though non-neurological factors such as joint stiffness can contribute. Hypertonia is a broad term that encompasses several distinct patterns of increased muscle tone.

The most commonly recognized forms are spastic hypertonia, dystonic hypertonia, and rigidity. Spastic hypertonia, or spasticity, is a velocity-dependent increase in tone with exaggerated stretch reflexes, typically arising from upper motor neuron lesions (for example, after stroke, brain injury, or cerebral palsy). Dystonic hypertonia involves sustained or intermittent involuntary muscle contractions that produce abnormal postures or twisting movements, often worsened by voluntary actions or particular tasks. Rigidity denotes a uniform increase in tone throughout the range of motion, not dependent on movement speed, and is usually associated with extrapyramidal disorders such as Parkinson disease. Paratonia and other complex presentations can occur in various neurological conditions as well.

Assessment relies on clinical examination and, when appropriate, standardized scales such as the Modified Ashworth Scale or the Tardieu scale to estimate tone and differentiate patterns. Hypertonia may coexist with contractures and requires consideration of neural and non-neural contributions.

Management is multidisciplinary and aims to reduce distress, improve function, and prevent contractures. Interventions include physical therapy, stretching, positioning, and orthotics; pharmacologic options such as oral antispastic agents (baclofen, tizanidine, dantrolene, benzodiazepines) and botulinum toxin injections for focal spasticity; intrathecal baclofen for severe generalized spasticity; and, in select cases, surgical or neuromodulation approaches.