Mandibular Osteomyelitis

Lesion caused by Actinomyces Bovis(Courtesy of Alun Williams (RVC))

• "Lumpy jaw"

Clinical

• Seen mainly in cattle and exotics caused by Actinomyces bovis producing osteomyelitis of mandible.
• Mostly young animals.
• Will not heal without treatment and jaw enlarges until animal cannot eat.

Pathogenesis

• Starts as alveolar periostitis of lower cheek teeth, due to ingestion of poor coarse roughage e.g. straw or hay with lots of thistles.
• Slowly enlarging mandible (occasionally maxilla) due to granulomatous inflammation producing much fibrous tissue.
• No real pus formation but "sulphur granules" in middle of lesion.
• Organism causes "pyogenic granuloma."

• Can grow to enormous size (e.g. size of grapefruit) and whole of mandible is blown apart by multiple foci of infection.

Also see:Actinobacillosis - "Wooden Tongue" (Courtesy of Alun Williams (RVC))

Pathology

3 major features:

1. Inflammatory removal of bone. As cortex of bone is pushed out by central inflammation produces thinning of bone cortex with proliferation of new periosteal bone. The centre of the mandible is eroded forming a honeycomb-like bone. Eventually will erode through bone producing granulomatous lesion on bottom of mandible and eventually eroding through skin.
2. Granuloma with micro abscess's in centre with greenish / yellow granules in middle of pus. These granules known as "sulphur bodies". Sulphur body is a colony of tangled mass of Actinomyces filaments. This is surrounded by neutrophils and macrophages forming a pyogenic granuloma.
3. Masses of fibrous tissue surround the granuloma and fill the spaces where bone has been destroyed.

• May extend to muscles, especially masseters, from osteomyelitis
• Histologically:
  • Caseous or suppurative centres of lesions
  • Epithelioid and giant cells at periphery
  • 'Sulfa granules' at centre - gram-positive branching rods