Muscle stiffness (synonym: rigidity) is seen in neurological diseases and takes two different forms: 1) spasticity or 2) rigidity.
Spasticity
This describes muscle cramping associated with paralysis (e.g. arm or leg weakness). Depending on the severity, the affected parts of the body show excessive muscle tension as a result of faulty control by the nerves. Various, often very serious diseases involving structural damage to the central nervous system can be the cause of this stiffness (e.g. stroke, multiple sclerosis, tumours, paraplegia, spinal stenosis, craniocerebral injury, etc.) Stiffness can also occur at the onset of amyotrophic lateral sclerosis (ALS).
Rigidity
This rather waxy type of stiffness is characteristic of Parkinson’s disease. Muscle stiffening (“rigidity”) is usually associated with a general lack of movement and slowing of movements (“akinesia”) and with tremor at rest. Dystonic “cramps” See dystonia.
