Epidural steatitis and vertebral osteomyelitis in a dog
History: A 1 year old spayed female bulldog mix canine became acutely non-ambulatory, and both rear limbs were hyporeflexive.
There was a 7 cm x 3 cm x 3 cm abscess in the epaxial musculature of the lumbar spine containing red-brown purulent fluid. The muscles surrounding the abscess including the epaxial and hypaxial musculature was pale, and there was a focal area of lysis of the ventral cortex of vertebral bodies L2 and L3.
The dura of the spinal cord from vertebral bodies L2-L5 was covered with a thick layer of organized fibrin and suppurative material causing compression of the spinal cord. There were no gross lesions in the intervertebral discs and spinal cord.
There were multifocal 3-5 mm round red nodules diffusely throughout the lung.
Epidural adipose: The epidural fat is infiltrated by large numbers of neutrophils, macrophages, lymphocytes and plasma cells with large amounts of fibrin and fibrous tissue. There are multiple bacterial colonies.
Vertebrae: The cortical bone is infiltrated and lysed by a large amount of neutrophils, macrophages and fibroblsats. There are large numbers of neutrophils surrounding bacterial colonies in the bone marrow of several vertebrae.
Bacterial colonies are composed of mixed gram positive rods and gram negative bacteria with the gram positive rods predominating. Similar bacterial colonies are present in the lungs and valvular thrombus.
Aerobic culture: A swab from the exudate covering the spinal cord grew Corynebacterium spp and an unidentified bacteria.
1. Spinal Cord: Fibrinosuppurative epidural steatitis, chronic, focally extensive with compression of spinal cord
2. Vertebral body: Suppurative osteomyelitis with bacterial colonies
3. Lung: Multifocal suppurative pneumonia
4. Heart, right AV valve: Focal valvular endocarditis (not pictured)
Microscopically the spinal column lesions are more chronic as evidenced by increased numbers of macrophages, lymphocytes, and fibroblast proliferation. Epidural steatitis can occur through direct extension of bacteria into the epaxial musculature or through hematogenous bacterial emboli. The infection spread into the vertebrae and epidural adipose tissue causing spinal cord compression and the neurologic signs noted in the history. Secondary bacteremia caused valvular endocarditis and embolic pneumonia.