Involuntary muscle contractions and tremors are poorly described in veterinary medicine and often their cause is unknown. Below is a brief overview.
Muscle
Myotonia:
Clinical sign of prolonged muscle contraction or delayed relaxation of muscle after voluntary movement or after mechanical or electrical stimulation. Not blocked after curare (meaning that the nerve or NMJ is not playing a role); strictly the muscle. A stiff gait, sudden onset of rigid limbs and generalized muscle hypertrophy are the most common symptoms.
- Inherited Congenital Myotonia- Chow Chow and Miniature Schnauzer
- Acquired Myotonia- secondary to hyperadrenocorticism (Cushings)
Nervous System
Tetanus
Clinical sign of sustained contraction of muscles (usually extensors) without relaxation
- Clostridium tetani toxin. Dog are very resistant to the toxin and cats are 10x more resistant than dogs. Clinical signs develop in usually 5- 10 days after infection. Symptoms consist of opisthotonus, inability to walk, rigid facial and masticatory muscles, risus sardonicus, and retraction of the eyes.Death can occur from respiratory failure. Excitement / stimulation can worsen signs. Treatment is largely supportive with antibiotics and possibly anti-toxin. The prognosis is guarded to often poor.
Tetany
Clinical sign of sustained contraction of muscles (usually extensors), that is variably intermittent and varies in severity.
- CKCS hypertonicity syndrome
- Scottie cramps
- Epileptoid cramping syndrome in Border Terriers
Myoclonus
Clinical sign of sudden contraction of a group of muscle cells, followed by immediate relaxation.
- Congenital action-related repetitive myoclonus
- Acquired Action-related repetitive myoclonus
- Toxins- can cause diffuse whole body action related tremor. Metaldehyde, pyrethrins, lead, hexachlorophene, chlorinated hydrocarbon, OP, mycotoxins
- Postural repetitive myoclonus (ex idiopathic head tremors, orthostatic tremors)
Veterinary Neurology 