Clonus means a deep tendon reflex is causing a muscle to involuntarily, repetitively and rhythmically contract and relax when stretched. This deep tendon reflex occurs because of some sort of neurological disorder or central nervous system problem. i.e. brain and spinal cord.
Clonus occurs because a deep tendon reflex is not properly inhibited, which causes spasticity and hypotonia of the targeted muscle. And it differs from myoclonus and fasciculations in that the muscle contractions are substantial and rhythmic rather than irregular or twitching.
Most with clonus won’t know they have it unless they are tested for it. Testing for clonus is done on the ankle, wrist or patella as a diagnostic tool for some sort of central nervous system health issue.
Some of the underlying health conditions that cause clonus deep tendon reflex are:
- ALS
- stroke
- meningitis
- brain tumor
- brain damage
- brain abscess
- cerebral palsy
- spinal stenosis
- spinal cord injury
- multiple sclerosis
- transverse myelitis
- spastic paraparesis
- serotonin syndrome
- Huntington’s disease
- traumatic brain injury
- hepatic encephalopathy
Because clonus often indicates a serious neurological problems, a simple, non invasive deep tendon reflex test is one of the ways to determine if further complex neurological testing is necessary.