Rhythmic reflex monophasic contractions and relaxations of hypertonic muscles in response to an abruptly applied and sustained strecth stimulus
Clonus is a rhythmical series of contractions in response to the maintenance of tension in a muscle, associated with increased gamma efferent discharge. It is elicitable when tendon reflexes are brisk after a corticospinal lesion
The word Clonus comes from the Greek word meaning "violent, confused motion. Significance of clonus is that it is a sign of neurological conditions, epecially associated with upper motor neuron lesions involving descending motor pathways
Clonus is a condition that produce involuntary muscle spasms and most commonly it affects the muscles at the end of a limb. Clonus mainly affects the knees, ankles, upper and lower arm muscles, and the jaw.
The basic abnormality in clonus is
1. alternate involuntary muscular contraction and relaxation in rapid succession.
2. a continuous rhythmic reflex tremor that is initiated by the spinal cord below an area of spinal cord injury, when set in motion by reflex testing.
Mechanism of clonus
The exact mechanism of clonus remains unclear. Two different hypotheses have been asserted regarding the development of clonus.
What are the association of clonus?
Clonus is always associated with
Sites for clonus examination in clinical neurology :
Medical conditions that can cause clonus include:
Organic clonus Functional clonus
Sustained Non sustained
Bilateral equal Unequal
Exaggerated reflexes Absent
Plantar extensor Flexor
Pseudoclonus
Clonus is a rhythmical series of contractions in response to the maintenance of tension in a muscle, associated with increased gamma efferent discharge. It is elicitable when tendon reflexes are brisk after a corticospinal lesion
The word Clonus comes from the Greek word meaning "violent, confused motion. Significance of clonus is that it is a sign of neurological conditions, epecially associated with upper motor neuron lesions involving descending motor pathways
Clonus is a condition that produce involuntary muscle spasms and most commonly it affects the muscles at the end of a limb. Clonus mainly affects the knees, ankles, upper and lower arm muscles, and the jaw.
The basic abnormality in clonus is
1. alternate involuntary muscular contraction and relaxation in rapid succession.
2. a continuous rhythmic reflex tremor that is initiated by the spinal cord below an area of spinal cord injury, when set in motion by reflex testing.
Mechanism of clonus
The exact mechanism of clonus remains unclear. Two different hypotheses have been asserted regarding the development of clonus.
- The most widely accepted explanation is that hyperactive stretch reflexes in clonus are caused by self-excitation.
- Another alternative explanation for clonus is central generator activity that arises as a consequence of appropriate peripheral events and produces rhythmic stimulation of the lower motor neurons.
What are the association of clonus?
Clonus is always associated with
- Brisk tendon reflex.
- Spasticity and
- Bablnski's sign-It is a very reliable sign of pyramidal tract lesion.
- Sustained clonus (true clonus).
- Unsustained clonus (pseudoclonus).
Unsustained clonus (≤5 beats): may be physiological
Sustained clonus (>5 beats): regarded as abnormal
Sites for clonus examination in clinical neurology :
- Ankle clonus.
- Patellar clonus.
- Jaw clonus (elicit the Jaw jerk to see a scries of closure and opening of the mouth).
- Wrist clonus (elicited by sudden passive extension of the fingers).
Medical conditions that can cause clonus include:
- Multiple sclerosis
- Huntington disease
- Spinal cord or brain injuries
- Stroke
- Meningitis
- Cerebral palsy
Organic clonus Functional clonus
Sustained Non sustained
Bilateral equal Unequal
Exaggerated reflexes Absent
Plantar extensor Flexor
Pseudoclonus