Rigidity, which is often used as a synonym to Hypertonia by many authors, is a common muscle tone disorder in which there is resistance to passive movement irrespective of posture and velocity. It is one of the cardinal features of Parkinson's Disease and is usually present in extrapyramidal disorders. It affects the agonists and the antagonists equally.
It can be seen in -
- Parkinson's Syndrome
- Corticobasal Degeneration
- Huntington's Disease
- Multiple System Atrophy
- Stiff Man/limb Syndrome
- Niemann-Pick Disease - Type A
- Orthostatic Hypotonia Shy-Drager Disease
- Spinocerebellar Ataxia - type 43, 17, 2
Rigidity is a hypertonic state characterized by constant resistance throughout range of motion that is independent of the velocity of movement. It is the result of excessive supraspinal drive (upper motor neuron facilitation) acting on alpha motor neurons; spinal reflex mechanisms are typically normal. In parkinsonian rigidity, tendon jerks are usually normal
'Rigidity" is defined as hypertonia in which all of the following are true:
- The resistance to externally imposed joint movement is present at very low speeds of movement, does not depend on imposed speed, and does not exhibit a speed or angle threshold
- Simultaneous co-contraction of agonists and antagonists may occur, and this is reflected in an immediate resistance to a reversal of the direction of movement about a joint
- The limb does not tend to return toward a particular fixed posture or extreme joint angle
- Voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen.
AnatomyThe “basal ganglia” refers to a group of subcortical nuclei responsible primarily for motor control, as well as other roles such as motor learning, executive functions and behaviors, and emotions. The classical basal ganglia model shows how information flows through the basal ganglia back to the cortex through two pathways with opposing effects for the proper execution of movement.
Rigidity is the result of excessive supraspinal drive (upper motor neuron facilitation) acting on alpha motor neurons; spinal reflex mechanisms are typically normal. There is a disruption of normal reciprocal inhibition. When the balance of inhibition and excitation in the basal ganglia and motor cortex is upset, the symptoms and signs of rigidity and involuntary movements supervene along with abnormalities of posture and associated movement. However, our current understanding of basal ganglia pathophysiology does not provide an adequate explanation for the two other cardinal features of Parkinson’s disease, namely, rigidity and tremor.
Several factors may contribute to rigidity of which some include -
- inability of the patient to relax and completely eliminate activity in the muscles
- increased stiffness due to altered viscoelastic properties of the muscles
- abnormal co-activation of agonist-antagonist muscle groups
- increased stretch reflexes
- decreased dopamine levels
Types of Rigidity
The rigidity of Parkinson disease may be characterized as either “lead pipe” or “cogwheel.”
- Cogwheel Rigidity - Refers to a hypertonic state with superimposed ratchet-like jerkiness and is commonly seen in upper extremity movements (e.g., wrist or elbow flexion and extension). The cogwheel type of rigidity is a combination of lead-pipe rigidity with tremor.
- Lead Pipe Rigidity - Refers to hypertonic state throughout the range of motion i.e simultaneous co-contraction of agonists and antagonists and this is reflected in an immediate resistance to a reversal of the direction of movement about a joint.
Difference between Spasticity and Rigidity
Spasticity generally occurs only during muscle stretch (i.e., not at rest) and is usually accompanied by increased tendon reflexes and a Babinski’s response. There is usually a difference between resistance in one direction of movement as compared to the opposite direction and some patients may represent with Clasp-Knife phenomenon (sudden release at end range of motion)In rigidity, muscle tone is increased even at rest and is usually presents during passive range of motion in all directions across individual joints. The plantar reflex and tendon reflexes are usually normal. There is absence of synergy.
The examiner should hold the hand of the patent above the wrist with one hand and keep it fixed. With other hand he grasps the fingers and the palm and then slowly rotate along the long axis of the hand. If there is rigidity, the examiner will experience resistance during the movement. If the cogwheel phenomenon is positive, the examiner will experience interruption or repeated catch during the movement and if present throughout without any interruption or change with respect to velocity, it is lead-pipe rigidity. Generally in case of idiopathic Parkinson disease only unilateral rigidity is seen which can be compared during the examination with the contralateral side.
Treatment of Parkinson disease with levadopa (L-Dopa) in these various combinations is extremely helpful in reducing bradykinesia and rigidity.
For most patients, treatment proceeds better if rigidity is decreased early in the treatment session. Thus, movement therapy interventions appear to have more lasting effects when the treatment is performed during the “on” phase of a medication cycle.
Relaxation techniques appear to be effective in reducing rigidity, including gentle, slow rocking, rotation of the extremities and trunk, and the use of yoga. In patients with Parkinson disease, relaxation may be better achieved in the sitting or standing positions because rigidity may increase in the supine position. Since the proximal muscles are often more involved than the distal muscles, relaxation may be easier to achieve by following a distal-to-proximal progression
Rhythmic Exercises are shown to decrease rigidityEg. Clapping hands, making circles with hands or feet.
Rhythmic initiation and Rhythmic rotation (Proprioceptive Neuromuscular Facilitation)
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