Acute Osteomyelitis
For Pharmacy Examining Board of Canada (PEBC) MCQ and EE Preparation
Introduction
Acute osteomyelitis is a bacterial infection of the bone that requires immediate medical attention. This chapter outlines the etiology, diagnosis, treatment options, and management strategies. It is tailored for candidates preparing for the Pharmacy Examining Board of Canada (PEBC) exams and is applicable for both multiple-choice questions (MCQ) and Evaluating Examinations (EE).
Goals of Therapy
The goals of treatment in acute osteomyelitis include:
Curing the infection: Eradicating the bacterial pathogen.
Minimizing morbidity: Preventing complications such as loss of limb function.
Preventing recurrence: Reducing the risk of progression to chronic osteomyelitis.
1. History
Symptom Duration:
Acute symptoms (lasting < 2 weeks): Fever, localized pain, redness, swelling, and potential loss of limb function or movement.
Chronic symptoms (> 2 weeks): May warrant referral to an infectious disease specialist. Evaluate for other causes such as tuberculosis or brucellosis.
Risk factors:
Recent surgery, trauma, or presence of foreign material.
Immunocompromised states such as sickle cell disease or diabetes.
For diabetic patients, consider diabetic foot infections (see relevant section).
2. Physical Examination
Tenderness: Exquisite tenderness over the affected bone.
Range of Motion: Limited movement in the affected limb.
Suspect Septic Arthritis: Warmth, erythema overlying a joint, or pseudoparalysis may indicate a need for urgent surgical referral.
3. Laboratory Tests
CBC and Acute-Phase Reactants: Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).
Blood Cultures: Positive in approximately 25-30% of cases.
Aspiration/Biopsy:
Ideally, obtain a bone or periosteal aspirate.
Avoid superficial wound cultures as they are unreliable and prone to contamination.
4. Imaging Studies
X-rays: Not sensitive in early disease; may show changes only after 10 days of infection.
MRI: Highly sensitive for diagnosing osteomyelitis and defining infection extent.
CT Scan: Consider if MRI is not available.
Bone Scan: Useful but less specific; often used in cases where MRI is unavailable or insufficient.
Non-Pharmacologic Management
Surgical Drainage
Surgical decompression may be required in the following scenarios:
If the patient is clinically unstable or septic.
Presence of pus on aspiration or abscess formation.
Delay in presentation or diagnosis.
Pharmacologic Management
Antibacterial therapy should be initiated after obtaining cultures when possible. Empiric intravenous (IV) antibacterial therapy is started based on the likely infecting organism, with definitive treatment tailored once culture results are available.
Empiric IV Antibacterial Therapy
Below is a table that provides empiric options based on the source of infection.
Source | Likely Organisms | Empiric IV Antibacterials |
Hematogenous (most common) | Staphylococcus aureus, Streptococcus, Kingella | Cloxacillin, Cefazolin, or Vancomycin if MRSA is suspected |
Post-traumatic or Contiguous | Polymicrobial: Staphylococcus, Gram-negative, Anaerobes | Amoxicillin-Clavulanate, Ceftriaxone + Metronidazole |
Penetrating Trauma | Pseudomonas, Staphylococcus aureus | Ceftazidime + Piperacillin/Tazobactam or Ciprofloxacin |
Diabetic Foot | Polymicrobial (Staphylococcus, Gram-negative, Anaerobes) | Ceftriaxone, Amoxicillin-Clavulanate, or Piperacillin/Tazobactam |
Algorithm for the Management of Acute Osteomyelitis
The following table summarizes the treatment approach from diagnosis to the evaluation of clinical response.
Step | Action |
1. Clinical Diagnosis | Symptoms suggestive of acute osteomyelitis based on history and examination. |
2. Investigations | CBC, CRP, ESR, blood cultures, X-ray, MRI, CT, or biopsy if needed. |
3. Surgical Aspiration ± Exploration | Obtain aspirate for Gram stain, cultures, or biopsy. |
4. Empiric IV Antibacterials | Start based on suspected organisms. Tailor once culture results are available. |
5. Evaluate Clinical Response | Assess improvement within a few days after starting antibacterials. |
6. If Clinical Response is Good | Transition to oral or continued IV therapy for 4-6 weeks. |
7. If No Improvement | Review antibacterial regimen, consider further surgery. |
Step-Down Therapy (IV to Oral)
Patients with a good clinical response may transition from IV to oral therapy, provided they meet the following criteria:
Clinical Stability: Absence of fever, improvement in local signs.
Source Control: Adequate surgical management or no need for further procedures.
Good Oral Absorption: Absence of gastrointestinal disorders affecting medication uptake.
Oral therapy options include:
For MSSA: Cloxacillin or Cephalexin.
For MRSA: Clindamycin, Doxycycline, or Trimethoprim-Sulfamethoxazole (for community-acquired MRSA).
For Gram-Negative Bacilli: Ciprofloxacin or Amoxicillin-Clavulanate.
Duration of Antibacterial Therapy
Treatment duration depends on the severity of infection:
Uncomplicated Cases: Typically 4 weeks of treatment is sufficient.
Severe or Resistant Infections: May require up to 6 weeks.
Penetrating Injuries: Shorter courses of 10-14 days may be sufficient if adequate debridement has been performed.
Follow-Up and Monitoring
Clinical Monitoring: Success is judged by resolution of fever, local inflammation, and return of function.
Laboratory Monitoring: ESR and CRP can help assess response to treatment. These markers should normalize over time.
Avoid Routine Follow-Up Imaging: Imaging is not necessary if the patient has shown clinical improvement, as radiologic changes may lag behind clinical response.