Osteomyelitis is either inflammation or infection of the bone. It is most commonly caused by a bacterial infection, although systemic fungal infection can also cause bone infections in cats.
The most common bacteria involved in osteomyelitis is Staphylcoccus sp, Streptococcus sp and Escherichia coli after trauma and/or surgery, and Proteus sp, Klebsiella sp, Pasteurella sp as well as anaerobes (bacteria that can live without oxygen) such as Actinomyces sp, Clostridium sp, and Bacteroides sp are common isolates from bite wounds.
Bone infection are more common cats than dogs due to cat bites during fighting. Entire male cats are at greater risk of developing puncture wounds from cat fights, and cats with compromised immune systems (such as FIV or FeLV) are more vulnerable to developing bacterial or fungal infections, however osteomyelitis can occur in cats of any age, sex and health status.
What are the causes of bone infections in cats?
Osteomyelitis has many possible causes, bones may become infected directly after surgery or trauma (where bacteria enters the site), or as a result of a systemic or local bacterial or fungal infection travelling to the bone through the blood stream. The most common causes of osteomyelitis are listed below:
- Puncture wounds, usually caused by another cat during a fight. The oral cavity has a high number of bacteria, when a puncture wound occurs, bacteria are injected into the skin and deeper layers
- Surgery such as treatment to repair fractured bones after a car accident which introduces bacteria to the site. Known as post-traumatic osteomyelitis.
- Prosthetic joint implants can cause osteomyelitis either by introducing bacteria during surgery (rare), or an inflammatory reaction to the implants (known as non-infectious osteomyelitis)
- Soft tissue infection which spreads to bones nearby
- Dental infection which can spread to the jawbone
- Systemic bacterial or fungal infection which spreads to the bone via the bloodstream
- Gunshot wounds
What are the symptoms of bone infection in cats?
Osteomyelitis can be acute (sudden onset) or chronic (waxing and waning over an extended period of time). The most common symptoms include lameness and pain. Other symptoms may include:
- Swelling around the affected area
- Draining tracts
- Pus may ooze from soft tissue surrounding the area
- Muscle atrophy (wasting)
- Swollen and painful joints close to the affected area
- Stiffness and reluctance to move
- Reluctance to put any weight on the affected leg
- Loss of appetite
If your cat has a systemic bacterial or fungal infection, additional symptoms may also be present.
How does the veterinarian diagnose a bone infection?
Your veterinarian will perform a physical examination of your cat and obtain a medical history from you including recent surgery, trauma or known infections as well as how long symptoms have been present. He will need to perform some diagnostic tests including:
- Complete blood count, biochemical profile and urinalysis which may reveal increased white blood cell count, which is indicative of an infection. Serum and urinalysis are usually unremarkable unless systemic infection or blood infection are present
- Bone x-rays can identify osteomyelitis but it may take some time for changes to appear in the bone
- MRI scans can be used to differentiate between soft tissue and bone infection
- Aerobic and anaerobic bacterial cultures may be taken to identify the organism. This enables your veterinarian to prescribe the most suitable antibiotic for that particular bacteria. Samples may be obtained from the infected site or bone biopsies collected
- If a fungal infection is suspected, specific blood tests to identify antibodies to certain fungal infection as well as additional x-rays and samples of any secretions or discharges (if present) which will be sent off for evaluation
- If systemic bacterial infection is suspected, a blood sample may be taken and cultured to identify the specific bacteria
How is bone infection treated in cats?
Antibiotic therapy is the treatment of choice for osteomyelitis. Preferably a culture will have been taken to determine the infectious agent involved and the appropriate antibiotic. Antibiotic administration is often prolonged as osteomyelitis can be difficult to treat. It should also be noted that recurrences can happen.
Surgical debridement to remove all necrotic tissue and thorough cleaning with sterile saline may be carried out.
If there is a fracture of the bone, your veterinarian will stablise it to ensure proper healing. In some cases an implant may be used. This will be removed once the bone has healed. Severe fractures may require amputation of the affected limb.
Regular follow up appointments will be required to closely monitor your cat's progress.
While your cat heals, he may be placed on cage rest to prevent accidental injury to the bone as it is healing.
Preventing bone infection in cats:
Often it is not possible to prevent this kind of infection, but some ways to reduce the chances of your cat developing a bone infection include:
- Thoroughly cleaning and applying a safe antiseptic to any bites, scratches or wounds
- Keep cats either indoors or in a cat enclosure to limit exposure to cars and other cats
- Prompt veterinary attention if your cat develops an abscess. Signs of an abscess include an area of swelling, pain and heat. Abscesses in location where there is underlying bone close to the site are particularly at risk
- Maintain good oral hygiene to limit his chances of developing a dental infection. Regularly check your cat's mouth for signs of inflammation or infection
- Always follow your veterinarian's instructions when giving antibiotics to your cat and ensure you give the entire course