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****Hyperplasia of spindle cells
 
****Hyperplasia of spindle cells
 
****Osteoid is produced
 
****Osteoid is produced
*[[More Hepatozoon|More detail on ''Hepatozoon americanum'']]
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*Myositis
 
*Myositis
 
**Develop cysts in skeletal muscle of dogs and cats
 
**Develop cysts in skeletal muscle of dogs and cats
 
**May be accompanied by pyogranulomatous myositis - macrophages and [[Neutrophils|neutrophils]] mainly with occasional other cells
 
**May be accompanied by pyogranulomatous myositis - macrophages and [[Neutrophils|neutrophils]] mainly with occasional other cells
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'''[Skeletal lesions of canine hepatozoonosis caused by Hepatozoon americanum. Panciera Rj et al. Vet Path (2000) 37 225-230]'''
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*[[Coccidia|'''''Hepatozoon americanum''''']]
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**SE USA
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**Clinical signs:
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***Fever
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***Weakness
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***Myalgia
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***Bone pain
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***Mature neutrophilic leukocytosis
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***Wasting
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***Poor response to treatment
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***Periosteal new bone formation
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**Much more aggressive and higher mortality rate than the disease in the Old World
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**Gross skeletal lesions:
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***Markedly thickened and edematous periskeletal soft tissue and periosteum of the lower legs ***+/- petechiation
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***Eccentrically or circumferentially arranged plaques of new bone formation deposited on the original cortex
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***Boney plaques look ‘porous’ to compact, often in layers with the spongey areas covered by more compact bone
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***No evidence of endosteal bone formation
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***Periosteoproliferative lesions most prominent in proximal long bones of the limbs (esp. femur and humerus)
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***Metaphyses usually spared
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***Caudal and lateral surfaces of the proximal tibia and fibular and radius and ulnar diaphyses affected
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***Distal diaphyses and metaphyses less severely affected/free from lesions
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***Metacarpals/tarsals mildly affected
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***Lateral surface of scapula affected
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***Axial skeleton less severely affected
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***Often bones of the skull prominently affected – orbits, rostrolateral maxilla and mandible, lateral aspect of zygomatic arch
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***Lateral aspects of vertebral arches and spinous processes sometimes affected
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***Ribs normal
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***Multifocal [[Muscles Inflammatory - Pathology#Parasitic myositis|parasitic myositis]]
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**Histologically:
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***Earliest change in periosteum -> swelling and hypertrophy of osteoprogenitor cells in the deeper layers of the periosteum
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***Spindle cells become stellate and plumper
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****Become aligned in single or multiple layers
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****Undergo hyperplasia creating a thick and densely cellular zone on the cortical surface
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***Osteoid is produced and osteoblasts become entrapped forming spiccules of trabecular new bone
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***New spicules arranged perpendicular to the cortical surface
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***With time, considerable osteoclastic activity, remodeling occurs firstly adjacent to the older cortex and then extends outwards
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***As the remodeling continues, the spicules become longitudinally arranged
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***Pseudocortices form that can contain bone marrow parenchyma
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***Endothelial hypertrophy prominent in vessels adjacent and within the periosteum
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***Severe edema present in adjacent soft tissue
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***Muscle atrophy and fibrosis often accompanied the edema
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***No evidence of inflammation
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***No parasites in adjacent muscle/soft tissue
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**Lesions develop in young dogs, within 5wks of experimental infection and progress rapidly, looking just like hypertrophic osteopathy
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**No obvious link between site of infection and generalized boney lesions
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*Differentials for periosteal new bone formation:
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**[[Bones Hyperplastic and Neoplastic - Pathology#Hypertrophic osteopathy|Hypertrophic osteopathy]]
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**[[Bones Hyperplastic and Neoplastic - Pathology#Craniomandibular osteopathy|Craniomandibular osteopathy]]
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**[[Panosteitis|Canine panosteitis]]
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**[[Bones Hyperplastic and Neoplastic - Pathology#Hypertrophic osteodystrophy|Hypertrophic osteodystrophy]]
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*Hypertrophic osteoarthropathy
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**V difficult to distinguish from this syndrome
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**Again no inflammation, histologically look identical, but these cases don’t have an abdominal/thoracic mass, and HO usually starts on the metacarpals/tarsals
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*?Pathogenesis
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**Thought to occur secondary to increased blood flow and fluid retention within the limbs, leading to vascular and then periosteal proliferation
       
[[Category:Miscellaneous Protozoa]][[Category:To_Do_-_Parasites]]
 
[[Category:Miscellaneous Protozoa]][[Category:To_Do_-_Parasites]]
 
[[Category:Bones - Pathology]]
 
[[Category:Bones - Pathology]]
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