Hypertonia

More a description than a diagnosis (as hypotonia), it presents as a marked increase in muscle tension (or tone) with spasticity or rigidity.  If the latter, the muscles are unable to stretch through a full range of motion that is velocity dependent as is typical of people with Parkinson’s disease (who can also show lead pipe rigidity: sustained resistance to passive movement that is independent of velocity).  Spasticity is a form of rigidity, but is only evident at the start of a passive movement and moreover is velocity dependent.  This is referred to as spastic hypertonia in contrast to dystonic hypertonia as displayed by Parkinson patients.  Hypertonia can arise, for example, from a blow to the head, a stroke, brain tumor, toxins, multiple sclerosis and in other neurodegenerative diseases (e.g., Parkinson’s disease), and as a consequence of neurodevelopmental abnormalities such as cerebral palsy (e.g., due to anoxic white matter damage in preterm infants).  There are lesions to the so-called upper motor neurons in the frontal lobe (neurons in the motor area of the cerebral cortex or brain stem, the main ones being Betz cells in the primary motor cortex).  The classification and definition of disorders associated with hypertonia are a topic of debate in pediatrics.