Clonus: definition, mechanism, treatment.

Area of Science:

• Neurology
• Neurophysiology
• Muscle Physiology

Background:

• Clonus is characterized by involuntary, rhythmic muscle contractions resulting from permanent damage to descending motor neurons.
• It can affect various muscles, including the ankle, patella, and wrist, typically at a frequency of 5-8 Hz.

Purpose of the Study:

• To explore the underlying mechanisms of clonus, including hyperactive stretch reflexes and central generator activity.
• To compare clonus burst durations with Soleus medium-latency reflex (MLR) to understand afferent involvement.

Main Methods:

• Analysis of clonus characteristics, including oscillation period and phase durations (plantar flexion and dorsiflexion).
• Comparison of clonus burst durations with Soleus medium-latency reflex (MLR) durations.
• Review of proposed hypotheses for clonus development: self-excitation via hyperactive stretch reflexes versus central generator activity.

Main Results:

• Ankle clonus oscillations have an average period of 160-200 ms, with plantar flexion comprising 45% and dorsiflexion 55%.
• The first clonus beat is longer, with subsequent beats shortening and stabilizing by the 4th or 5th cycle.
• Clonus burst durations exceed those of the Soleus MLR, suggesting involvement of various afferent pathways and spinal mechanisms beyond Ia afferents.

Conclusions:

• The precise mechanism of clonus remains incompletely understood, with ongoing debate between self-excitation and central generator theories.
• Clonus shares similarities with the Soleus MLR, but differences in stretch speed and cause indicate distinct pathways and potential involvement of group II afferents.
• Treatment options for clonus include pharmacological agents like baclofen, physical interventions such as cold application, and injections like botox or phenol.