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Tremors and Movement Disorders (Nervous System) - Pathology (view source)

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==Tetanus==
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* In a pathological context, '''"tetanus" is an infectious disease caused by the bacterium [[Clostridium species#Clostridium tetani|''Clostridium tetani'']]'''.
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** Physiologically, the term "tetanus" refers to continuous sustained muscle contraction.
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*** The disease caused by [[Clostridium species#Clostridium tetani|''Clostridium tetani'']] is characterised by this feature.
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===Pathogenesis===
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* [[Clostridium species#Clostridium tetani|''Clostridium tetani'']] generally cause infection via wound contamination.
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** Cuts or deep puncture wounds are most commonly infected.
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* [[Clostridium species#Clostridium tetani|''Clostridium tetani'']] produces tetanospasmin, a neurotoxin.
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** Tetanospasmin inhibits the release of the neurotransmitters GABA and glycine from interneurons in the spinal cord and brain.
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* Without the usual inhibitory influence of glycine and GABA, there is increased excitation of the brainstem and motor neurons.
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** This leads to unopposed muscle contraction.
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*** The frequency of action potentials at the neuromuscular junctions increases above a threshold.
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*** Above this threshold, muscle fibres enter a state of tetanus.
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**** Muscle spasm is initially present in the muscles of the jaw.
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**** This is followed by a difficulty in [[Deglutition|swallowing]].
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**** General muscle stiffness and spasms then develop in other parts of the body.
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** Other effects may include:
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*** Seizures
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*** Effects on the autonomic nervous system
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===Diagnosis===
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* Diagnosis is made by taking into account the animal's:
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**  History
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** Clinical signs
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* Very rarely a wound where the bacteria may have entered may be seen.
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===Treatment===
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* Wound debridement
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** Surgical removal of dead and infected tissue from the wound.
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* Antibiotic treatment.
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** Metronidazole
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*** Treatment with metronidazole decreases the number of bacteria but has no effect on the bacterial toxin.
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*** Metronidazole is particularly active against anaerobic bacteria, and so is a good choice for use against [[Clostridium species#Clostridium tetani|''C. tetani'']]
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** Penicillin
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*** Penicillin is becoming a less favoured treatment for tetanus, since there is a theoretical risk of increased spasms.
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* Muscle relaxants
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** Diazepam
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** Midazolam
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* Supportive therapy, for example:
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** Administering fluids
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** Providing appropriate nutrition
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** Maintaining a quiet environment with dimmed light.
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* Remission take several weeks to months
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==Tetany==
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* Tetany is variable intermittent muscle contraction.
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===Causes===
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* Stricnine poisoning.
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* Hypocalcemia
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** For example, due to:
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*** Parturition
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*** Hypothyroidism
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* Glycine disorders, in:
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** Humans
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*** Knowns as startle  disease or hyperexplexia.
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*** Causes sudden contraction of primarily antigravity muscles
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** Arabian horses
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==Myoclonus==
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* Myoclonus is sudden contraction of muscle followed by relaxation.
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* There are several different types of myoclonus.
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** Sporadic
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** Repetitive
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** Constant
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** Action related
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*** Congenital
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*** Acquired
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** Postural
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** Episodic
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** Resting
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===Sporadic Myoclonus===
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* Sporadic myoclonus occurs as a reflex response.
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** A sudden response to an auditory stimulus.
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===Repetitive Myoclonus===
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* In repetitive myoclonus, contractions and relaxations are rhythmic.
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** They occur one to two seconds apart.
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** May occur when the animal is at rest or during movement.
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* Repetitive myoclonus may be due to a functional disturbance of lower motor neurons.
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** This may be caused, for example, by distemper or another encephalomyelitis.
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===Action-Related Myoclonus===
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* Tremors are induced by movement.
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** Myoclonus disappears when the patient is relaxed or sleeping.
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* May be caused by:
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** Cerebellar conditions
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** Myelin defects
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** Toxic insult
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** Problems with neurons
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====Congenital====
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* Results from:
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** Hypo- or dys-myelination
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** Storage diseases
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* Samoyeds, springer spaniels and dalmations are predisposed.
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====Acquired====
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* Maltese terrtiers and West Highland white terriers are predisposed.
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** Gives rise to the name "white shakers" for the sufferers.
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* Caused by meningoencephalitis.
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** Toxicosis is a common cause of meningoencephalitis, for example:
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*** Metaldehyde
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*** Pyrethrins
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*** Hexachlorophene
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*** Organophosphate
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*** Food born mycotoxins
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*** Macadamia nuts
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* Takes the form of postural repetitive myoclonus.
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** Postural muscles are affected while they are supporting weight.
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* The young and old are differentially affected.
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** Young animals
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*** The head and neck are affected.
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**** Gives head bobbing, which stops when the animal is distracted.
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*** Most common in Dobermans, English Bulldogs and Boxers.
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** Aged dogs
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*** Pelvic limbs are affected, although only when standing.
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**** Orthostatic tremors
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*** Whole muscles are affected.
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*** Most common in Great Danes.
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* Aquired action-related myoclonus is responsive to steroid or immunosuppressive drugs.
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===Other Conditions Giving Myoclonus===
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* Scottie cramp
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* Cavalier King Charles Spaniel hypertonicity
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* Norwich terriers have a predisposition.
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