Clonus - The maximum hyperexcitability!
“rhythmic involuntary muscular contractions induced by the sudden passive stretching of a muscle or tendon”
2) Electrodiagnostic “ankle clonus soleus rectified EMG and position of the ankle are displayed superimpose. Soleus muscle activity can be seen after ankle dorsiflexion”
3) Frequency
4) Pseudoclonus
- psychogenic disorders
- poorly sustained and irregular in rate, rhythm and excursion
- ankle clonus; true clonus can usually be stopped by sharp passive plantar flexion of the foot or great toe while the false clonus remains unaltered.
5) Pathophysiology
UMN lesions cause an ⬆️ in gamma motor neuron activity and a decrease in inhibitory interneuron (renshaw cell) activity, resulting in a state of hyperexcitability of alpha motor neurons.
New Zealand neurologist Derek Ernest Denny-Brown (1901–1981)
6) Ankle clonus
7) Ankle clonus
8) Patellar clonus
9) Patellar clonus
10) Elbow clonus
11) Wrist clonus
12) Wrist clonus
13) Wrist clonus
14) Jaw clonus
15) Jaw clonus
16) Jaw clonus
17) Where would the upper motor neuron lesion need to be to get this response?
- strongly suggests a lesion of the pyramidal tract
"all types of clonus lesions are in CST, except the jaw clonus, which is related to the corticopontine tract"