YR3 15 M HO2

Question 1

Bacterial Myositis

Answer 1

Difficult for bacteria to colonize healthy muscles even when bacteremia occurs how ever Clostridial bacteria are good at colonizing hypoxic muscle

Question 2

Blackleg; pathogenesis

Answer 2

Clostridium chauvoei spores eaten and
remain dormant in oxygenated muscle > Traumatic muscle injury results in muscle hypoxia > Spores germinate and bacteria proliferate > Toxins cause vasoconstriction resulting in more muscle hypoxia and inhibiting inflammation > Animals die rapidly due to toxaemia

Question 3

Blackleg; gross, histo

Answer 3

Gross - Emphysematous necrosis - dark muscle w/ numerous gas bubbles. Rancid butter smell present.
Histo - Acute muscle necrosis, fibrin and proliferating clostridial bacteria

Question 4

Gas gangrene; pathogenesis

Answer 4

Environmental clostridia (most notably C.
septicum) invade deep penetrating
wounds > Wounds have local hypoxia allowing
proliferation > Toxin production causes further necrosis and inhibits inflammation > Death often rapid due to toxaemia

Question 5

Gas gangrene; gross

Answer 5

Oedema, emphysema and haemorrhage. Offensive Odour

Question 6

Big Head

Answer 6

Specific type of gas gangrene usually caused by C. novyi > Tissue damage occurs due to head-butting in sheep

Question 7

Big Head; gross

Answer 7

Swelling and emphysema around head

Question 8

Wooden tongue

Answer 8

Usually involves CT of the
tongue, but can extend to a glossal
myositis > Caused by infection of cuts by
Actinobacillus lignieresii

Question 9

Parasitic Myositis

Answer 9

1)Trichinella
2)Cysticercosis - Sheep measles caused by Cysticercus ovis
3)Sarcocystosis - Usually incidental, but can develop a ‘hypersensitivity reaction’ resulting in marked
eosinophilic myositis
4)Neospora - More commonly neuritis although protozoa can be visible in muscle, calf/lamb foetus

Question 10

Immune-mediated myositis - Polymyositis

Answer 10

Mostly in dogs; results initially in muscle
inflammation, pain, and swelling > followed by fibrosis and atrophy.
Multifocal multiphasic necrosis

Question 11

Immune-mediated myositis - Masticatory Myositis

Answer 11

Autoimmunity against type II masticatory

myosin - protein restricted to masticatory muscles > Eosinophilic myositis followed by > Fibrosis

Question 12

Immune-mediated myositis - Extraocular Myositis

Answer 12

Exophthalmus (bulging of the eye) caused by muscle swelling

Question 13

Metabolic myopathy - VitE/Selenium deficiency; aka, animal, agent

Answer 13

White Muscle disease/Nutritional myopathy, usually affect neonatal or young animals.
Lack of free radical savaging > oxidative muscle necrosis - more active the muscle = more free radicals = more severe lesions

Question 14

Metabolic myopathy - VitE/Selenium deficiency; gross, outcome

Answer 14

1)Gross - Muscle Pallor Visible
> Young Animals - tongue, diaphragm, heart
> Older Animals - thigh, shoulder, costal muscles
2)Histo - Multifocal multiphasic necrosis w/ calcification, myocyte necrosis, macrophage infiltration & fibrosis
3)Outcome - death due to heart failure or respiratory failure caused by costal muscle damage. Rigor mortis does not occur in severely affect animals

Question 15

Metabolic myopathy - Iron myopathy in piglets

Answer 15

Iron is a pro-oxidant > xs. Iron predisposes to muscle necrosis (appearance & pathogenesis similar to white muscle disease)

Question 16

Metabolic myopathy - Monensin toxicity; species, use, toxicity

Answer 16

1) Horses > Dogs & Pigs > Cattle & Chicken
2) Used as a feed efficiency promoter
3) Toxicity > Horses are fed cattle ration / accidental mixing of rations / dogs scavenge monensin boluses

Question 17

Metabolic myopathy - Monensin toxicity; pathogenesis

Answer 17

Monensin prevents muscle producing ATP > ATP essential for maintaining cell integrity > Diarrhoea, colic & death after 24hrs
Gross - incomplete rigor mortis w/ pale & swollen muscles
Histo - Multifocal monophasic necrosis
Sublethal dose > death by congestive heart failure due to cardiac necrosis and subsequent fibrosis”

Question 18

Skeletal Muscle Neoplasia - Benign tumours

Answer 18

1) Laryngeal rhabdomyoma – dogs

2) Cardiac rhabdomyoma – pigs, cattle, sheep

Question 19

Skeletal Muscle Neoplasia - Malignant tumours

Answer 19

1)Rhabdomyosarcomas uncommon aggressive
tumours in all species
2)Botryoid rhabdomyosarcomas involve the bladder in young dogs (bunches of grapes)