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