How Do I Examine Rigidity and Spasticity?

Examination of tone (increased resistance to the passive movement of a joint) is a clinically useful and occasionally neglected part of the neurological examination. Rigidity and spasticity are two distinct types of hypertonia that arise from distinct anatomical pathways. The ability to differentiate between these two entities therefore gives important information regarding localization. Whereas spasticity arises as a result of damage to the corticoreticulospinal (pyramidal) tracts, rigidity is caused by dysfunction of extrapyramidal pathways, most commonly the basal ganglia, but also as a result of lesions of the mesencephalon and spinal cord. Spasticity is characterized by abnormally high muscle tone, which often asymmetrically affects antagonistic muscle groups. It is both amplitude and velocity dependent and is therefore best assessed using rapid movements of the relevant joint to effect abrupt stretching of the muscle group involved. When a threshold velocity, angle, or amplitude is reached, a sudden increase in tone can be detected as a characteristic "catch." Rigidity differs from spasticity in that the increased tone remains constant throughout the range of movement of the joint. It is independent of velocity and should even be detectable with very slow movements. It is present in flexors and extensor muscle groups equally, giving rise to a uniform quality in all directions often described as "lead pipe" rigidity. Given that rigidity frequently arises in diseases of the basal ganglia, a tremor can coexist, giving rise to an interrupted "cogwheeling" effect. We herein describe an approach to the examination of patients with rigidity and spasticity.