Osteomyelitis in Dogs and Cats

Osteomyelitis is inflammation and infection of the medullary cavity, cortex, and periosteum of bone, most frequently associated with bacteria, fungi, or viruses.

This condition can arise from various sources, including hematogenous spread, direct trauma, and iatrogenic causes, such as after surgery.

The most common bacteria associated with osteomyelitis in cats and dogs are listed below, with Staphylococcus spp accounting for 50% of cases:

• Staphylococcus spp

• Streptococcus spp

• Escherichia coli

• Proteus spp

• Pasteurella spp

• Pseudomonas spp

• Brucella canis

Anaerobic bacteria are less frequently isolated and may be part of a polymicrobial infection.

Fungal diseases are based on geographic distributions and include the following:

• Coccidioides immitis (southwestern US)

• Blastomyces dermatitidis (southeastern US)

• Histoplasma capsulatum (central US)

• Cryptococcus neoformans

• Aspergillus spp (worldwide)

Factors contributing to infection include ischemia, trauma, focal inflammation, bone necrosis, and hematogenous spread.

Clinical signs can be acute or chronic. Animals may have lameness, pain, edema, or purulent discharge; systemic clinical signs are possible and may include fever, anorexia, and depression.

Radiography can reveal bone lysis, sequestration, and irregular periosteal reaction (see Osteomyelitis, radiograph, dog); loosening of implants is common, and fistulous tracts may be observed. Deep fine-needle aspiration, cytological evaluation, and urine and blood cultures may also help identify the causative agent and determine antimicrobial susceptibility.

Osteomyelitis, radiograph, dog

Image

Courtesy of Dr. Ronald Green.

Treatment includes both medical and surgical therapies. Empirical antimicrobial therapy is necessary for acute cases with systemic clinical signs while waiting for the culture and susceptibility report. The antimicrobials of choice are broad-spectrum bactericidal agents that are beta-lactamase resistant. Clavulanic acid/amoxicillin (15 mg/kg, PO, every 12 hours until clinical resolution), cephalexin (22–30 mg/kg, PO, every 8–12 hours until clinical resolution), and clindamycin (11–33 mg/kg, PO, every 12 hours for 28 days) are used in both dogs and cats (1, 2, 3, 4). Enrofloxacin (10 mg/kg, PO, every 12 hours until clinical resolution) is used only in mature dogs to avoid damage to developing cartilage (5).

For chronic osteomyelitis without systemic clinical signs, culture and susceptibility–based antimicrobial therapy is ideal to prevent development of resistant bacteria. Close monitoring of response to treatment is necessary to ensure effective treatment. Wound debridement, lavage, and removal of nidus (such as loose implants) are recommended. Open or closed wound drainage and delayed autogenous, cancellous bone grafting can also be performed. In chronic, refractory cases, limb amputation may be warranted.

The prognosis is variable and based on the severity and chronicity of the infection. Appropriate antimicrobial therapy based on bacterial culture and antimicrobial susceptibility testing is mandatory for successful results.