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Hypertonia is a term sometimes used synonymously with spasticity in the literature surrounding damage to the central nervous system, namely upper motor brain lesions.〔http://www.ninds.nih.gov/disorders/hypertonia/hmypertonia.htm〕 Impaired ability of damaged motor neurons to regulate descending pathways gives rise to disordered spinal reflexes, increased excitability of muscle spindles, and decreased synaptic inhibition. These consequences result in abnormally increased muscle tone of symptomatic muscles.〔Sheean, G. & McGuire, J. R. (2009). Spastic hypertonia and movement disorders; Pathophysiology, clinical presentation, and quantification. American Academy of Physical Medicine of Rehabilitation, 1, 827-833.〕 Some authors suggest that the current definition for spasticity, the velocity-dependent over-activity of the stretch reflex, is not sufficient as it fails to take into account patients exhibiting increased muscle tone in the absence of stretch reflex over-activity. They instead suggest that “reversible hypertonia” is more appropriate and represents a treatable condition that is responsive to various therapy modalities like drug and/or physical therapy.〔Bakeheit, A. M. O, Fheodoroff, K. & Molteni, F. (2011). Spasticity or reversible muscle hypertonia? Journal of Rehabilitation Medicine, 43, 556-557.〕 Symptoms associated with central nervous systems disorders are classified into positive and negative categories. Positive symptoms include those that increase muscle activity through hyper-excitability of the stretch reflex (i.e., rigidity and spasticity) where negative symptoms include those of insufficient muscle activity (i.e. weakness) and reduced motor function.〔Sanger, T. D., Chen, D., Delgado, M. R., Gaebler-Spira, D., Hallett, M., & Mink, J. W., (2006). Definition and classification of negative motor signs in childhood. Pediatrics, 118, 2159-2167〕 Often the two classifications are thought to be separate entities of a disorder; however, some authors propose that they may be closely related.〔Damiano DL, Dodd K, Taylor NF. Should we be testing and training muscle strength in cerebral palsy? Dev Med Child Neurol. 2002;44:68 –72〕 ==Pathophysiology== Hypertonia is caused by upper motor neuron lesions which may result from injury, disease, or conditions that involve damage to the central nervous system. Motor neuronal hyperactivity occurs due to loss of inhibition of cells of the anterior horn of the spinal cord resulting from reticulospinal tract damage. Different patterns of muscle weakness or hyperactivity can occur based on the location of the lesion, causing a multitude of neurological symptoms, including spasticity, rigidity, or dystonia.〔Geoffrey Sheean, MD, John R. McGuire, MD (2009) Spastic Hypertonia and Movement Disorders: Pathophysiology, Clinical Presentation, and Quantification〕 Spastic hypertonia involves uncontrollable muscle spasms, stiffening or straightening out of muscles, shock-like contractions of all or part of a group of muscles, and abnormal muscle tone. It is seen in disorders such as cerebral palsy, stroke, and spinal cord injury. Rigidity is a severe state of hypertonia where muscle resistance occurs throughout the entire range of motion of the affected joint independent of velocity. It is frequently associated with lesions of the basal ganglia. Individuals with rigidity present with stiffness, decreased range of motion and loss of motor control. Dystonic hypertonia refers to muscle resistance to passive stretching (in which a therapist gently stretches the inactive contracted muscle to a comfortable length at very low speeds of movement) and a tendency of a limb to return to a fixed involuntary (and sometimes abnormal) posture following movement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hypertonia」の詳細全文を読む スポンサード リンク
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