Clonus

What is Clonus?

Clonus is defined as a series of involuntary muscle contractions and relaxations that occur in a rhythmic pattern. These contractions are typically triggered by a sudden stretch of the muscle and can be observed in various muscle groups, most commonly in the ankles, wrists, and knees. Clonus is often associated with upper motor neuron lesions, which can result from various neurological conditions (Kandel et al., 2013).

Types of Clonus

Clonus can be classified based on the muscle groups involved and the characteristics of the contractions:

1. Ankle Clonus: This is the most common form of clonus, where rhythmic contractions occur in the ankle muscles. It is often tested during neurological examinations by rapidly dorsiflexing the foot.
2. Wrist Clonus: Similar to ankle clonus, this involves rhythmic contractions in the wrist muscles. It can be observed when the wrist is flexed or extended.
3. Generalized Clonus: This type involves multiple muscle groups and can be more challenging to assess. It may occur in severe neurological conditions.
4. Clonus Associated with Spasticity: In some cases, clonus may be accompanied by spasticity, where muscles are continuously contracted, leading to stiffness and difficulty in movement.

Causes of Clonus

1. Multiple Sclerosis (MS): MS can lead to demyelination of nerve fibers, resulting in upper motor neuron signs, including clonus (Compston & Coles, 2008).
2. Stroke: A stroke can damage areas of the brain responsible for motor control, leading to clonus in the affected limbs (Mackintosh et al., 2015).
3. Spinal Cord Injury: Damage to the spinal cord can disrupt normal motor pathways, resulting in clonus (Kumar et al., 2016).
4. Cerebral Palsy: This group of disorders affects movement and muscle tone, often leading to clonus in affected individuals (Bax et al., 2005).
5. Amyotrophic Lateral Sclerosis (ALS): ALS can cause degeneration of motor neurons, leading to various motor symptoms, including clonus (Rowland & Shneider, 2001).
6. Traumatic Brain Injury (TBI): TBI can result in upper motor neuron lesions, leading to clonus (Kumar et al., 2016).
7. Other Conditions: Other potential causes include brain tumors, infections, and metabolic disorders.

Examination Methods 

1. Physical Examination: A healthcare provider will perform a physical examination, looking for signs of clonus during the assessment of muscle tone and reflexes.
2. Deep Tendon Reflex Testing: The examiner may test deep tendon reflexes, such as the patellar reflex, to assess the integrity of the reflex arc and identify any abnormalities.
3. Ankle Clonus Test: To assess ankle clonus, the examiner will hold the patient’s foot in a neutral position and then rapidly dorsiflex the foot. If clonus is present, the foot will exhibit rhythmic contractions.
4. Wrist Clonus Test: Similar to the ankle test, the examiner will flex the wrist and observe for rhythmic contractions.
5. Neurological Imaging: In some cases, imaging studies such as MRI or CT scans may be performed to identify underlying causes of clonus, such as lesions or structural abnormalities in the brain or spinal cord.
6. Electromyography (EMG): EMG can be used to assess the electrical activity of muscles and help differentiate between upper and lower motor neuron lesions (Kandel et al., 2013).

Management and Treatment of Clonus

1. Physical Therapy: Physical therapy can help improve muscle strength, coordination, and overall mobility (Bourke et al., 2014).
2. Medications: Muscle relaxants, such as baclofen or tizanidine, may be prescribed to reduce muscle spasms and clonus (Kumar et al., 2016).
3. Botulinum Toxin Injections: In some cases, botulinum toxin injections may be used to target specific muscles and reduce spasticity and clonus (Dressler & Adib Saberi, 2014).
4. Occupational Therapy: Occupational therapy can assist individuals in adapting to their condition and improving daily functioning.
5. Surgical Interventions: In severe cases, surgical options may be considered to address underlying structural issues contributing to clonus.

References

• Bax, M., Tydeman, G., & Flodmark, O. (2005). Clinical and MRI definitions of cerebral palsy. Developmental Medicine & Child Neurology, 47(8), 508-512.
• Bourke, J. H., et al. (2014). The role of physical therapy in the management of spasticity. Neurorehabilitation and Neural Repair, 28(3), 217-224.
• Compston, A., & Coles, A. (2008). Multiple sclerosis. The Lancet, 372(9648), 1502-1517.
• Dressler, D., & Adib Saberi, F. (2014). Botulinum toxin in the treatment of spasticity. Current Opinion in Neurology, 27(5), 516-520.
• Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2013). Principles of Neural Science. McGraw-Hill.
• Kumar, R., et al. (2016). Clonus: A review of the literature. Journal of Clinical Neuroscience, 31, 1-5.
• Mackintosh, J. A., et al. (2015). The role of clonus in the assessment of spasticity. Journal of Rehabilitation Medicine, 47(5), 401-406.
• Rowland, L. P., & Shneider, N. A. (2001). Amyotrophic lateral sclerosis. New England Journal of Medicine, 344(22), 1688-1700.