What are the clinical differences between spasticity and rigidity?

From the Guidelines

Spasticity and rigidity are distinct forms of increased muscle tone that can be differentiated through clinical examination, with spasticity presenting as velocity-dependent resistance to passive movement and rigidity involving constant resistance throughout the range of motion regardless of speed. The clinical differences between spasticity and rigidity are crucial for accurate diagnosis and appropriate treatment selection. Spasticity typically affects antigravity muscles (flexors in upper limbs, extensors in lower limbs) and features the "clasp-knife" phenomenon where initial resistance suddenly gives way, as noted in guidelines for adult stroke rehabilitation and recovery 1. In contrast, rigidity affects flexors and extensors equally, occurs with basal ganglia disorders like Parkinson's disease, and is often accompanied by bradykinesia and tremor but normal reflexes, as described in the context of Parkinsonian syndromes 2.

Some key characteristics of spasticity include:

• Velocity-dependent resistance to passive movement
• Affects antigravity muscles
• Features the "clasp-knife" phenomenon
• Associated with upper motor neuron lesions, hyperreflexia, clonus, and positive Babinski signs
• Can be treated with targeted injection of botulinum toxin, oral antispasticity agents, and physical modalities such as NMES or vibration, as recommended in guidelines for adult stroke rehabilitation and recovery 1

In contrast, rigidity is characterized by:

• Constant resistance throughout the range of motion regardless of speed
• Affects flexors and extensors equally
• Often described as "lead-pipe" rigidity
• Associated with basal ganglia disorders like Parkinson's disease
• Often accompanied by bradykinesia and tremor but normal reflexes, as noted in the context of Parkinsonian syndromes 2

The underlying pathophysiology differs as well, with spasticity resulting from loss of descending inhibitory pathways after corticospinal tract damage, and rigidity stemming from basal ganglia dysfunction causing excessive muscle activation. These distinctions are crucial for accurate diagnosis and appropriate treatment selection, as highlighted in guidelines for adult stroke rehabilitation and recovery 1 and the evaluation of Parkinsonian syndromes 2.

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 FDA drug label does not answer the question.

From the Research

Clinical Differences between Spasticity and Rigidity

The clinical differences between spasticity and rigidity are distinct and can be identified through various methods.

• Spasticity is characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome 3.
• 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 4.
• Spasticity often asymmetrically affects antagonistic muscle groups and is associated with varying degrees of paresis, resulting in the syndrome of spastic paresis 5.

Rigidity

• Rigidity, on the other hand, 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 4.
• It is characterized by a uniform increase in tone that remains constant throughout the range of movement of the joint, independent of velocity 4.
• Rigidity 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.

Key Differences

• The key differences between spasticity and rigidity lie in their underlying mechanisms, clinical presentation, and response to treatment 3, 4, 5, 6, 7.
• Spasticity is typically associated with upper motor neuron lesions, while rigidity is associated with extrapyramidal pathway dysfunction 4.
• Treatment approaches also differ, with spasticity often managed with oral medications, physical modalities, and invasive procedures, while rigidity may be treated with medications targeting the basal ganglia and other extrapyramidal pathways 3, 6.