Episode 173: Acute Osteomyelitis

Future Dr. Tran explains the pathophysiology of osteomyelitis and describes the presentation, diagnosis and management of acute osteomyelitis. Dr. Arreaza provides information about

Written by Di Tran, MSIII, Ross University School of Medicine. Editing and comments by Hector Arreaza, MD.

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What is osteomyelitis?

Osteomyelitis, in simple terms, is an infectious disease that affects both bone and bone marrow and is either acute or chronic. According to archaeological findings of animal fossils with a bone infection, osteomyelitis was more than likely to be known as a “disease for old individuals”.Our ancestors over the years have used various vocabulary terms to describe this disease until a French surgeon, Dr. Nelaton, came up with the term “Osteomyelitis” in 1844.

This is the beauty of medical terms, Latin sounds complicated for some people, but if you break up the term, it makes sense: Osteo = bone, myelo = marrow, itis = inflammation. So, inflammation of the bone marrow.

Traditionally, osteomyelitis develops from 3 different sources:

First category is the “hematOgenous” spread of the infection within the bloodstream, as in bacteremia. It is more frequent in children and long bones are usually affected. [Arreaza: it means that the infection started somewhere else but it got “planted” in the bones]
Second route is “direct inoculation” of bacteria from the contiguous site of infection “without vascular insufficiency”, or trauma, which may occur secondary to fractures or surgery in adults. In elderly patients, the infection may be related to decubitus ulcers and joint replacements.
And the third route is the “contiguous” infection “with vascular insufficiency”, most seen in a patient with a diabetic foot infection.

Patients with vascular insufficiency often have compromised blood supply to the lower extremities, and poor circulation impairs healing. In these situations, infection often occurs in small bones of the feet with minimal to no pain due to neuropathy.They can have ulcers, as well as paronychia, cellulitis, or puncture wounds.

Thus, the importance of treating onychomycosis in diabetes because the fungus does not cause a lot of problems by itself, but it can cause breaks in the nails that can be a port of entry for bacteria to cause severe infections. Neuropathy is an important risk factor because of the loss of protective sensation. Frequently, patients may step on a foreign object and not feel it until there is swelling, purulent discharge, and redness, and they come to you because it “does not look good.”

Acute osteomyelitis often takes place within 2 weeks of onset of the disease, and the main histopathological findings are microorganisms, congested blood vessels, and polymorphonuclear leukocytes, or neutrophilic infiltrates.

What are the bugs that cause osteomyelitis?

Pathogens in osteomyelitis are heavily depended on the patient’s age. Staph. aureus is the most common culprit of acute hematogenous osteomyelitis in children and adults. Then comes Group A Strep., Strep. pneumoniae, Pseudomonas, Kingella, and methicillin-resistant Staph. aureus. In newborns, we have Group B Streptococcal.

Less common pathogens are associated with certain clinical presentations, including Aspergillus, Mycobacterium tuberculosis, and Candida in the immunocompromised.Salmonella species can be found in patients with sickle cell disease, Bartonella species in patients with HIV infection, and Pasteurella or Eikenella species from human or animal bites.

It is important to gather a complete medical history of the patient, such as disorders that may put them at risk of osteomyelitis, such as diabetes, malnutrition, smoking, peripheral or coronary artery disease, immune deficiencies, IV drug use, prosthetic joints, cancer, and even sickle cell anemia. Those pieces of information can guide your assessment and plan.

What is the presentation of osteomyelitis?

Acute osteomyelitis may present symptoms over a few days from onset of infection but usually is within a 2-week window period. Adults will develop local symptoms of erythema, swelling, warmth, and dull pain at the site of infection with or without systemic symptoms of fever or chills.Children will also be present with lethargy or irritability in addition to the symptoms already mentioned.

It may be challenging to diagnose osteomyelitis at the early stages of infection, but you must have a high level of suspicion in patients with high risks. A thorough physical examination sometimes will show other significant findings of soft tissue infection, bony tenderness, joint effusion, decreased ROM, and even exposed bone.

Diagnosis.

As a rule of thumb, the gold standard for the diagnosis of osteomyelitis is bone biopsy with histopathology findings and tissue culture. There is leukocytosis, but then WBC counts can be normal even in the setting of acute osteomyelitis.Inflammatory markers (CRP, ESR) are often elevated although both have very low specificity.

Blood cultures should always be obtained whenever osteomyelitis is suspected. A bone biopsy should also be performed for definitive diagnosis, and specimens should undergo both aerobic and anaerobic cultures. In cases of osteomyelitis from diabetic foot infection, do the “probe to bone” test. What we do is we use a sterile steel probe to detect bone which is helpful for osteomyelitis confirmation.

Something that we can’t miss out on is radiographic imaging, which is quite important for the evaluation of osteomyelitis. Several modalities are useful and can be used for the work-up plan; plain radiographs often are the very first step in the assessment due to their feasibility, low cost, and safety. Others are bone scintigraphy, CT-scan, and MRI. In fact, the MRI is widely used and provides better information for early detection of osteomyelitis than other imaging modalities. It can detect necrotic bone, sinus tracts, and even abscesses. We look for soft tissue swelling, cortical bone loss, active bone resorption and remodeling, and periosteal reaction. Oftentimes, plain radiography and MRI are used in combination.

Treatment:

Treatment of osteomyelitis actually is a teamwork effort among various medical professionals, including the primary care provider, the radiologist, the vascular, the pharmacist, the podiatrist, an infectious disease specialist, orthopedic surgeons, and the wound care team.

Something to take into consideration, if the patient is hemodynamically stable it is highly recommended to delay empirical antibiotic treatment 48-72 hours until a bone biopsy is obtained. The reason is that with percutaneous biopsy ideally done before the initiation of antibiotic treatment, “the microbiological yield will be higher”.We’ll have a better idea of what particular bugs are causing the problem and guide the treatment appropriately.

The choice of antibiotic therapy is strongly determined by susceptibilities results. The antibiotic given will be narrowed down only for the targeted susceptible organisms. In the absence of such information, or when a hospitalized patient presents with an increased risk for MRSA infection, empiric antibiotic coverage is then administered while awaiting culture results.

It should be broad-spectrum antibiotics and include coverage for MRSA, broad gram-negative and anaerobic bacteria. For example, vancomycin plus piperacillin-tazobactam, or with broad-spectrum cephalosporin plus clindamycin. Treatment will typically be given for 4 to 6 weeks.

The duration between 4-6 weeks is important for complete healing, but a small study with a small sample showed that an even shorter duration of 3 weeks may be effective, but more research is needed.

In certain situations, surgery is necessary to preserve viable tissue and prevent recurrent infection, especially when there are deep abscesses, necrosis, or gangrene, amputation or debridement is deemed appropriate.

If the infected bone is completely removed, patients may need a shorter course of antibiotics, even a few days only. Amputation can be very distressing, especially when we need to remove large pieces of infected bone, for example, a below-the-knee amputation. We need to be sensitive to the patient’s feelings and make a shared decision about the best treatment for them.

In patients with diabetes, additional care must be taken seriously, patient education about the need for compliance with treatment recommendations, with careful wound care, and good glycemic control are all beneficial for the healing and recovery process.

Because this is a very common problem in the clinic and at the hospital, we must keep our eyes wide open and carefully assess patients with suspected osteomyelitis to detect it promptly and start appropriate treatment. Adequate and timely treatment is linked to fewer complications and better outcomes.

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Conclusion: Now we conclude episode number 173, “Acute Osteomyelitis.” Future Dr. Tran explained the pathophysiology, diagnosis, and management of osteomyelitis. A bone biopsy is the ideal method of diagnosis. Delaying an...