Gunner is an 5 year old male German Shorthaired Pointer dog with a chronic history of lumbar pain without neurologic deficits that has been transiently responsive to aspirin therapy. Screening radiographs of the lumbar spine were initially normal. After several weeks of symptomatic therapy a lumbar MRI revealed a marked proliferative response involving the 3rd lumbar vertebra. The response was primarily periosteal and endosteal and the spinal canal was not involved. An increased fluid signal in the vertebral body with the appearance of a draining tract ventrally encased in a "spondylitic reaction" was noted. The lesion's appearance and location were considered classic for vertebral osteomyelitis from an inhaled foreign body that lodges at the attachment of the diaphragm.
Actinomyces spp. are commensal bacteria commonly found in the oral cavity of most mammals. Infection is thought to occur in an opportunistic fashion when the organism is directly implanted in devitalized tissue. The most common clinical forms of actinomycosis in dogs involve the cervicofacial region, thorax, abdomen, vertebral bodies and limbs. Infections involving the vertebrae usually occur retroperitoneally along the ventral aspects of the bodies of T(13)-L(3). In some cases grass awns have been found in these lesions. Theoretically contaminated grass awns could migrate to this location through the lung and the dorsal attachment of the diaphragm or through the intestines and the attachment of the root of the mesentery. Hunting breeds of dog appear to have the highest prevalence of disease, which may be attributable to an increased exposure to grass awns.