Osteomyelitis

Pathogenesis and epidemiology: Osteomyelitis cases can be classified by pathogenesis, duration of infection, location of infection, and whether prosthetic material is present. Osteomyelitis is typically caused by hematogenous spread, spread from a contiguous site following surgery, and/or secondary infection in the setting of vascular insufficiency or concomitant neuropathy (e.g., in diabetes). The most common primary foci of infection are the urinary tract, skin and soft tissues, intravascular catheterization sites, and the endocardium. Hematogenous osteomyelitis in adults most commonly results in vertebral infection, with 6.5 cases/100,000 at ages >70 years.
Microbiology: Irrespective of the anatomic location involved, S. aureus is the most common cause, accounting for ~40-50% of cases.
- - Gram-negative bacilli account for 10-20% of cases.
Clinical manifestations: Pts generally have a febrile illness, with localized pain and tenderness. A history of surgery or trauma in the affected region—even in the remote past—should raise suspicion.
Diagnosis: Radiographic studies and occasionally invasive sampling of lesions are needed to confirm the diagnosis.
- - Blood cultures are positive in 30-78% of cases, with lower rates if the pt has previously received antibiotics.
- - CT and especially MRI scans offer increased sensitivity in detecting osteomyelitis.
Treatment:Table 84-2 lists antibiotics for the treatment of osteomyelitis in the absence of implants.
- - The optimal route and duration of therapy remain controversial, but a 6-week course of IV therapy is usually recommended for acute osteomyelitis. If evidence indicates clinical efficacy of an oral antibiotic to which the organism is susceptible and if the pt has normal intestinal function (without vomiting), a transition from IV to PO therapy can be considered.
- - Serial measurements of inflammatory markers (ESR, C-reactive protein) can serve as surrogates for response to treatment in some infections (particularly those due to S. aureus).
- - Surgical intervention is usually required in chronic osteomyelitis and cases involving prosthetic implants.

For a more detailed discussion, see Stevens DL: Infections of the Skin, Muscles, and Soft Tissues, Chap. 156, p. 827; Madoff LC: Infectious Arthritis, Chap. 157, p. 833; and Zimmerli W: Osteomyelitis, Chap. 158, p. 838, in HPIM-19.

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