Myoclonus
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- Myoclonus is sudden contraction of muscle followed by relaxation.
- There are several different types of myoclonus.
- Sporadic
- Repetitive
- Constant
- Action related
- Congenital
- Acquired
- Postural
- Episodic
- Resting
Sporadic Myoclonus
- Sporadic myoclonus occurs as a reflex response.
- A sudden response to an auditory stimulus.
Repetitive Myoclonus
- In repetitive myoclonus, contractions and relaxations are rhythmic.
- They occur one to two seconds apart.
- May occur when the animal is at rest or during movement.
- Repetitive myoclonus may be due to a functional disturbance of lower motor neurons.
- This may be caused, for example, by distemper or another encephalomyelitis.
Action-Related Myoclonus
- Tremors are induced by movement.
- Myoclonus disappears when the patient is relaxed or sleeping.
- May be caused by:
- Cerebellar conditions
- Myelin defects
- Toxic insult
- Problems with neurons
Congenital
- Results from:
- Hypo- or dys-myelination
- Storage diseases
- Samoyeds, springer spaniels and dalmations are predisposed.
Acquired
- Maltese terrtiers and West Highland white terriers are predisposed.
- Gives rise to the name "white shakers" for the sufferers.
- Caused by meningoencephalitis.
- Toxicosis is a common cause of meningoencephalitis, for example:
- Metaldehyde
- Pyrethrins
- Hexachlorophene
- Organophosphate
- Food born mycotoxins
- Macadamia nuts
- Toxicosis is a common cause of meningoencephalitis, for example:
- Takes the form of postural repetitive myoclonus.
- Postural muscles are affected while they are supporting weight.
- The young and old are differentially affected.
- Young animals
- The head and neck are affected.
- Gives head bobbing, which stops when the animal is distracted.
- Most common in Dobermans, English Bulldogs and Boxers.
- The head and neck are affected.
- Aged dogs
- Pelvic limbs are affected, although only when standing.
- Orthostatic tremors
- Whole muscles are affected.
- Most common in Great Danes.
- Pelvic limbs are affected, although only when standing.
- Young animals
- Aquired action-related myoclonus is responsive to steroid or immunosuppressive drugs.
Other Conditions Giving Myoclonus
- Scottie cramp
- Cavalier King Charles Spaniel hypertonicity
- Norwich terriers have a predisposition.