What is the difference between spasticity and rigidity?

From the Guidelines

Spasticity and rigidity are two distinct types of muscle tone abnormalities with different causes, characteristics, and treatment approaches, and it is crucial to differentiate between them to provide appropriate management and improve patient outcomes. The key difference between spasticity and rigidity lies in their definitions and clinical presentations. Spasticity is defined as velocity-dependent hyperactivity of tonic stretch reflexes, characterized by increased resistance to passive movement that varies with the speed of movement, often accompanied by a "clasp-knife" phenomenon 1. On the other hand, rigidity is constant resistance throughout the range of motion, regardless of speed, and is often described as "lead-pipe" rigidity or, when combined with tremor, "cogwheel" rigidity.

Causes and Characteristics

• Spasticity typically affects specific muscle groups, particularly flexors in the upper limbs and extensors in the lower limbs, and is caused by damage to the corticospinal tract in conditions like stroke, multiple sclerosis, or spinal cord injury 1.
• Rigidity, however, affects agonist and antagonist muscles equally and stems from basal ganglia dysfunction in conditions like Parkinson's disease.

Treatment Approaches

• The treatment of spasticity often involves a stepwise approach, starting with the least invasive modalities such as positioning, passive stretching, and range of motion exercises, and progressing to more invasive treatments like oral medications (e.g., baclofen, tizanidine) or botulinum toxin injections 1.
• Targeted injection of botulinum toxin into localized upper or lower limb muscles is recommended to reduce spasticity and improve range of motion or gait function, with a Class I, Level A evidence recommendation 1.
• Rigidity, on the other hand, typically responds to dopaminergic medications like levodopa.

Clinical Implications

Understanding the differences between spasticity and rigidity is essential for proper diagnosis and treatment selection, as the underlying pathophysiology involves different neural pathways—upper motor neuron damage for spasticity versus basal ganglia dysfunction for rigidity. This distinction can significantly impact patient outcomes in terms of morbidity, mortality, and quality of life, highlighting the need for accurate diagnosis and tailored treatment approaches.

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 main difference between spasticity and rigidity is not explicitly stated in the provided drug labels. However, based on the context, it can be inferred that:

• Spasticity refers to a condition characterized by increased muscle tone, flexor spasms, and pain.
• Rigidity is mentioned as a symptom that can be alleviated by baclofen, but its distinct characteristics are not clearly defined in the provided text. Since the FDA label does not explicitly and directly address the question, no conclusion can be drawn about the specific differences between spasticity and rigidity 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.
• Rigidity, on the other hand, is a type of hypertonia that is independent of velocity and remains constant throughout the range of movement of the joint 4.

Causes and Pathophysiology

• Spasticity arises as a result of damage to the corticoreticulospinal (pyramidal) tracts, while rigidity is caused by dysfunction of extrapyramidal pathways, most commonly the basal ganglia 4.
• Spasticity is part of the upper motor neurone syndrome, manifesting as increased tone, clonus, spasms, spastic dystonia, and co-contractions 5.
• Rigidity in Parkinson's disease is associated with velocity-dependent abnormal neuronal activity and correlates with clinical score of rigidity 6.

Clinical Features and Examination

• Spasticity presents as upper motor neuron symptoms in patients with central nervous system pathology, such as stroke, spinal cord injury, brain injury, or multiple sclerosis 3.
• Rigidity is often described as "lead pipe" rigidity, with a uniform quality in all directions, and can be accompanied by a tremor, giving rise to an interrupted "cogwheeling" effect 4.
• Examination of tone is a clinically useful part of the neurological examination, and the ability to differentiate between spasticity and rigidity gives important information regarding localization 4.

Management and Treatment

• Management of spasticity involves identification and elimination of triggers, neurophysiotherapy, oral medications, focal injection of botulinum toxin, and surgical resection of selected dorsal roots of the spinal cord 5.
• Treatment options for spasticity also include oral medications, such as baclofen, tizanidine, and dantrolene, as well as interventional procedures, such as intrathecal baclofen pump and selective dorsal rhizotomy 3.