Review Question - QID 217731

This patient presenting with dull right leg pain and tenderness, erythema, warmth, swelling, fever, chills, tachycardia, and restricted range of motion due to pain (refuses to plantarflex or evert his ankle, indicating peroneal muscle involvement) in the setting of a neutrophilic leukocytosis and elevated inflammatory markers (ESR, CRP) most likely has acute hematogenous osteomyelitis. The most common cause of acute hematogenous osteomyelitis is Staphylococcus aureus.

Acute hematogenous osteomyelitis occurs commonly in children, due to hematogenous seeding of metaphyseal bone. The long bones of the appendicular skeleton are commonly affected in the pediatric population. The microbiology of this condition varies according to predisposing factors, but the most common etiology is S. aureus. Streptococcus pyogenes and Kingella kingae are less common causes. Group B streptococcus is the most common cause in neonates whereas Salmonella is an important cause in patients with sickle cell hemoglobinopathies. The diagnostic workup consists of a careful history to elicit predisposing factors and blood cultures. Biopsy of the affected site can assist in making a microbiological diagnosis. Radiographs of the affected area can be obtained, which can show soft tissue edema and bony involvement (areas of lucency, cortical disruption, periosteal reaction). If radiographs are negative, this is followed by advanced imaging (e.g., magnetic resonance imaging), as radiography is not sensitive, especially in the early stages of the disease.

Conrad discusses the pathophysiology, diagnosis, and management of acute hematogenous osteomyelitis. The author notes that Staphylococcus aureus is the most common etiology in all age groups.

Incorrect Answers:
Answer 1: Polymicrobial organisms are common causes of acute and chronic osteomyelitis in patients with diabetic foot wounds due to poor vascularity and impaired immunity at the site. Common organisms include Staphylococci sp., Streptococci sp., enterococci, and anaerobic organisms. These patients are typically older adults who have a chronic history of poorly maintained diabetes mellitus. Empiric treatment is with broad-spectrum antibiotic coverage.

Answer 2: Pseudomonas aeruginosa can cause osteomyelitis in the setting of puncture wounds of the foot. Deep foot puncture wounds are treated with foreign body removal and surgical debridement, which can yield a microbiological diagnosis via culture. Antibiotic coverage should include anti-pseudomonal coverage (e.g., piperacillin-tazobactam, meropenem).

Answer 3: Salmonella spp. are an important cause of osteomyelitis in patients with sickle cell hemoglobinopathies. However, Staphylococcus aureus is still the most common cause of osteomyelitis even in these patients.

Answer 5: Streptococcus pyogenes is a less common cause of osteomyelitis than Staphylococcus aureus and therefore is less likely in this patient.

Bullet Summary:
Staphylococcus aureus is the most common cause of acute hematogenous osteomyelitis in all age groups.