Tremors and Movement Disorders (Nervous System) - Pathology

Tetanus

In a pathological context, "tetanus" is an infectious disease caused by the bacterium Clostridium tetani.
- Physiologically, the term "tetanus" refers to continuous sustained muscle contraction.
  - The disease caused by Clostridium tetani is characterised by this feature.

Clostridium tetani generally cause infection via wound contamination.
- Cuts or deep puncture wounds are most commonly infected.
Clostridium tetani produces tetanospasmin, a neurotoxin.
- Tetanospasmin inhibits the release of the neurotransmitters GABA and glycine from interneurons in the spinal cord and brain.
Without the usual inhibitory influence of glycine and GABA, there is increased excitation of the brainstem and motor neurons.
- This leads to unopposed muscle contraction.
  - The frequency of action potentials at the neuromuscular junctions increases above a threshold.
  - Above this threshold, muscle fibres enter a state of tetanus.
    - Muscle spasm is initially present in the muscles of the jaw.
    - This is followed by a difficulty in swallowing.
    - General muscle stiffness and spasms then develop in other parts of the body.
- Other effects may include:
  - Seizures
  - Effects on the autonomic nervous system

Diagnosis is made by taking into account the animal's:
- History
- Clinical signs
Very rarely a wound where the bacteria may have entered may be seen.

Wound debridement
- Surgical removal of dead and infected tissue from the wound.
Antibiotic treatment.
- Metronidazole
  - Treatment with metronidazole decreases the number of bacteria but has no effect on the bacterial toxin.
  - Metronidazole is particularly active against anaerobic bacteria, and so is a good choice for use against C. tetani
- Penicillin
  - Penicillin is becoming a less favoured treatment for tetanus, since there is a theoretical risk of increased spasms.
Muscle relaxants
- Diazepam
- Midazolam
Supportive therapy, for example:
- Administering fluids
- Providing appropriate nutrition
- Maintaining a quiet environment with dimmed light.
Remission take several weeks to months

Stricnine poisoning.
Hypocalcemia
- For example, due to:
  - Parturition
  - Hypothyroidism
Glycine disorders, in:
- Humans
  - Knowns as startle disease or hyperexplexia.
  - Causes sudden contraction of primarily antigravity muscles
- Arabian horses

Sporadic myoclonus occurs as a reflex response.
- A sudden response to an auditory stimulus.

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.

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

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
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.
- Aged dogs
  - Pelvic limbs are affected, although only when standing.
    - Orthostatic tremors
  - Whole muscles are affected.
  - Most common in Great Danes.
Aquired action-related myoclonus is responsive to steroid or immunosuppressive drugs.