From the Guidelines
Spasticity and rigidity are distinct types of muscle tone abnormalities with different causes and characteristics, and understanding this distinction is crucial for proper diagnosis and management. Spasticity is velocity-dependent resistance to passive movement, meaning the faster a limb is moved, the more resistance is felt, often with a "catch" followed by relaxation (clasp-knife phenomenon) 1. It results from upper motor neuron damage in conditions like stroke, multiple sclerosis, or cerebral palsy, and primarily affects antigravity muscles. Rigidity, by contrast, is constant resistance throughout the range of motion regardless of speed, often described as "lead-pipe" rigidity or, when tremor is present, "cogwheel" rigidity. It stems from basal ganglia dysfunction in conditions like Parkinson's disease or neuroleptic malignant syndrome. Some key points to consider when differentiating between spasticity and rigidity include:
- The velocity-dependent nature of spasticity, which is not present in rigidity 1
- The presence of a "catch" or clasp-knife phenomenon in spasticity, which is not typically seen in rigidity 1
- The primary involvement of antigravity muscles in spasticity, whereas rigidity can affect a wider range of muscle groups 1 Treatment approaches differ: spasticity may respond to baclofen, tizanidine, or botulinum toxin injections, while rigidity typically requires dopaminergic medications like levodopa 1. In terms of management, the most recent guidelines recommend a stepwise approach, beginning with the least-invasive modalities and progressing to more invasive, with a focus on addressing the underlying causes of spasticity or rigidity and improving functional outcomes 1. Overall, a thorough understanding of the differences between spasticity and rigidity is essential for providing effective care and improving patient outcomes.
From the FDA Drug Label
Indications and Usage Baclofen tablets are useful for the alleviation of signs and symptoms of spasticity resulting from multiple sclerosis, particularly for the relief of flexor spasms and concomitant pain, clonus, and muscular rigidity. The difference between spasticity and rigidity is not explicitly defined in the provided drug label.
- Spasticity is mentioned as a condition that baclofen tablets are useful for alleviating.
- Rigidity is mentioned as a symptom that baclofen tablets can provide relief for, in addition to spasticity. Since the FDA label does not directly address the question of what the difference is between spasticity and rigidity, no conclusion can be drawn 2.
From the Research
Definition and Characteristics
- Spasticity is a velocity-dependent increase in muscle tone and uncontrolled, repetitive, involuntary contractions of skeletal muscles 3.
- It is characterized by abnormally high muscle tone, which often asymmetrically affects antagonistic muscle groups, and is both amplitude and velocity dependent 4.
- Spasticity is typically assessed using rapid movements of the relevant joint to effect abrupt stretching of the muscle group involved, and a sudden increase in tone can be detected as a characteristic "catch" 4.
Comparison with Rigidity
- Rigidity is a distinct type of hypertonia that arises from dysfunction of extrapyramidal pathways, most commonly the basal ganglia, and is characterized by a constant increase in tone throughout the range of movement of the joint 4.
- Unlike spasticity, rigidity is independent of velocity and is present in flexors and extensor muscle groups equally, giving rise to a uniform quality in all directions often described as "lead pipe" rigidity 4.
- Rigidity frequently coexists with tremor, giving rise to an interrupted "cogwheeling" effect, whereas spasticity is not typically associated with tremor 4.
Clinical Implications
- The ability to differentiate between spasticity and rigidity is important for localization and diagnosis, as spasticity arises from damage to the corticoreticulospinal (pyramidal) tracts, while rigidity is caused by dysfunction of extrapyramidal pathways 4.
- Accurate diagnosis and differentiation between spasticity and rigidity can inform treatment decisions, as different treatments may be effective for each condition 3, 5, 6, 7.