Which individual is most at risk to develop osteomyelitis caused by Staphylococcus aureus?

Summary

Despite important medical and surgical advances in management of patients, osteomyelitis remains extremely difficult to treat. The relapse rate can be as high as 20%. The optimal management of osteomyelitis requires a multidisciplinary team of physicians, including an orthopedic surgeon, neurosurgeon, oral surgeon, plastic surgeon, vascular surgeon, invasive radiologist, and infectious disease specialist. The usual goal of therapy is the eradication of the infection and restoration of function. Treatment of chronic osteomyelitis usually requires aggressive surgical débridement and prolonged antimicrobial therapy.

Treatment

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Surgical debridement in biopsy-positive cases will guide direction for antibiotic therapy. This will vary with type of osteomyelitis. Duration of therapy is usually 4 to 6 wk for acute osteomyelitis; chronic osteomyelitis may need a longer course of medication

Orthopedic hardware should be removed if possible

S. aureus (MSSA): Cefazolin IV, nafcillin IV, vancomycin IV (in patient allergic to penicillin)

S. aureus (MRSA): Vancomycin IV, linezolid IV or PO, daptomycin IV

Streptococcus spp: Ceftriaxone, IV penicillin G in sensitive species

P. aeruginosa: Cefepime, imipenem/cilastatin, or meropenem

Enterobacteriaceae: Ceftriaxone or ertapenem

Anaerobes: Clindamycin, piperacillin-tazobactam, cefotetan, or metronidazole

Table 2 summarizes antimicrobial therapy for selected microorganisms in osteomyelitis. A retrospective analysis1 revealed that in diabetic foot osteomyelitis adjunctive rifampin is associated with improved amputation-free survival

Hyperbaric oxygen therapy: May be useful in chronic osteomyelitis

Wound-assisted vacuum device may help closure of wound

Surgical debridement of all devitalized bone and tissue

Immobilization of affected bone (plaster, traction) if bone is unstable

FUNGI

Osteomyelitis may be caused by numerous endemic and opportunistic fungal agents, including C. immitis, cryptococci, Candida spp., Blastomyces spp., and Aspergillus spp. Coccidioidomycosis may be characterized by cough, chest pain, night sweats, and anorexia, and it often is associated with erythema nodosum or erythema multiforme. This disease commonly is found in the southwestern United States. Extrapulmonary involvement is suggested by persistent high temperature and toxicity. C. immitis occurs primarily in cancellous bone (e.g., vertebral bodies, distal tubular bones, and the skull).167 These lesions are not radiographically distinct from the lesions seen in osteomyelitis from other causes.183 Débridement of bone lesions often is needed initially, and years of therapy are required. Oral triazole agents generally are recommended.74

Blastomycosis may mimic coccidioidomycosis, but the pulmonary involvement is much more varied, and fusion of the vertebral bodies rarely occurs. A propensity for the development of verrucous, reddened, weeping skin lesions has been noted, and prostate involvement may be seen. Bone involvement occurs frequently, with the skull and vertebral bodies being infected most often. Distinguishing it from other forms of osteomyelitis is impossible by radiographic examination.

Aspergillus osteomyelitis is being recognized with increasing frequency.35 Most commonly, it is a disease of immunosuppressed patients, with Aspergillus pneumonia seen initially followed by disseminated disease. Bone disease occurring by hematogenous spread has developed, however, in normal individuals and after injectable drug use.43,172 Aspergillus osteomyelitis developing after trauma also has been reported.

Other fungi are causes of osteomyelitis. The medical literature contains dozens of reports of osteomyelitis caused by C. neoformans, generally in immunocompromised patients and in the setting of disseminated or pulmonary infection. The few reports in pediatric patients generally have involved immunocompromised adolescents. In adolescents and adults, usually only one bone is involved. The lesions generally are slowly destructive, very discrete lesions occurring primarily in the long tubular bones without marginal sclerosis. This radiologic reaction is confused most commonly with tumor and, occasionally, with tuberculosis. Infection of the ribs and skull also has been reported. Although experience with this disease is limited, débridement of the lesions and medical therapy seem to be highly effective.14,30,37,84,131,132 Cases of Rhizopus osteomyelitis have been reported intermittently and apparently are hematogenous in origin.57

Differential Diagnosis

Distinguishing osteomyelitis from cellulitis or trauma (accidental or abuse) is the most common clinical circumstance. Myositis or pyomyositis can also appear similar to osteomyelitis with fever, warm and swollen extremities, and limping; tenderness to palpation of the affected soft tissue area is generally more diffuse than noted in acute osteomyelitis. Nevertheless, distinguishing myositis and pyomyositis from osteomyelitis clinically may be difficult. Myositis and pyomyositis may be isolated but are often found adjacent to an osteomyelitis on MRI. Pyomyositis is most often caused byS. aureus, followed by group A streptococcus. The pelvic muscles are a common site of pyomyositis and can mimic a pelvic osteomyelitis. MRI is the definitive study to identify and localize pelvic pyomyositis (Fig. 704.5). An iliopsoas abscess can manifest with thigh pain, limp, and fever and must be considered in the differential diagnosis of osteomyelitis. The iliopsoas abscess may be primary (hematogenous:S. aureus) or secondary to infection in adjacent bone(S. aureus), kidney(E. coli) or intestine (E. coli,Bacteroides spp.).Mycobacterium tuberculosis has been reported in patients with HIV infection. Any child with negative x-ray imaging and a negative hip aspiration, who presents with fever, limp, and elevated inflammatory marks should be evaluated for pyomyositis.

Appendicitis, urinary tract infection, and gynecologic disease are among the conditions in the differential diagnosis of pelvic osteomyelitis. Children with leukemia commonly have bone pain or joint pain as an early symptom. Neuroblastoma with bone involvement may be mistaken for osteomyelitis. Primary bone tumors need to be considered, but fever and other signs of illness are generally absent except in Ewing sarcoma. In patients with sickle cell disease, distinguishing bone infection from infarction may be challenging.

Chronic recurrent multifocal osteomyelitis (CRMO) is a nonpyrogenic, sterile inflammatory bone disease that is considered an autoinflammatory disorder (seeChapter 188). It is also associated with a family history of autoimmune disease; the affected patient may also have other inflammatory diseases such as Crohn disease, Sweet syndrome, psoriasis, and palmar plantar pustulosis. CRMO in children has many similarities with synovitis, acne, pustulosis, hyperostosis, and osteitis syndrome (SAPHO), seen in adults. In addition, CRMO has similarities to Majeed syndrome, an autosomal recessive disorder with a microcytic dyserythropoietic anemia and with a deficiency of interleukin-1 receptor antagonist, an autosomal recessive autoinflammatory disease.

In contrast to infectious osteomyelitis, CRMO is multifocal and recurrent and may involve bones not typical of osteomyelitis (spine, pelvis, clavicle, mandible, calcaneus). Plain radiographs reveal osteolytic lesions or sclerosis; whole body short tau inversion recovery MRI imaging is the diagnostic study of choice (Fig. 704.6).

DISCUSSION

Osteomyelitis is an inflammatory condition involving the medullary cavity of bone that begins as a bacterial infection and can cause significant bony destruction. The microorganisms cause host tissue injury from direct cellular attack and through enzymatic degradation. The host responds by recruiting neutrophils to the area to digest the pathogens via release of enzymes and phagocytosis. When purulence (composed of necrotic tissue, dead bacteria, and WBCs) accumulates, it causes an increase in the intramedullary pressure, causing collapse of the vessels, venous stasis, and congestion. Vessels within the haversian system and Volkmann's canals of the cortical bone may undergo thrombosis or experience stasis and congestion, resulting in the surrounding bone becoming ischemic and thereby permitting the extension of osteomyelitis. If purulence continues to accumulate, the periosteum is penetrated and mucosal or cutaneous fistulas develop.

The establishment of an infection within bone is related to the compromise in the bone's vascular supply, but other factors, such as the virulence of the organism and the integrity of the host defenses, are also important. Host factors include systemic diseases with a microvascular component (e.g., diabetes), blood dyscrasias (e.g., sickle cell disease), immunosuppression (e.g., HIV infection), and collagen vascular disorders or bone dysplasias (e.g., osteopetrosis).

Initially, Staphylococcus aureus and Staphylococcus epidermidis accounted for 80% to 90% of osteomyelitis of the jaws. However, the frequency of S. aureus involvement in osteomyelitis has decreased due to the improved culture methods used to identify organisms, especially anaerobes. Anaerobes are frequently associated with aerobic organisms in osteomyelitis. Currently, osteomyelitis is recognized as a disease commonly caused by streptococci (α-hemolytic) and oral anaerobes such as Peptostreptococcus, Fusobacterium, and Prevotella.

SPECIAL CLINICAL SITUATIONS

Chronic Recurrent Multifocal Osteomyelitis

Chronic recurrent multifocal osteomyelitis (CRMO) is generally considered to be noninfectious, occurs more commonly in girls younger than 10 years old, and is associated with palmoplantar pustulosis, psoriasis vulgaris, and Sweet's syndrome (acute febrile neutrophilic dermatosis). CRMO is characterized by recurrent episodes of fever, swelling, and pain, usually at more than one site. Plain radiographs often demonstrate multiple areas of osteolysis and sclerosis, especially in the long bones and clavicles. Diagnosis may be difficult, but long-term prognosis is generally good. Treatment includes nonsteroidal anti-inflammatory agents and possibly steroids; in most cases antibiotics are not helpful.

DIAGNOSTIC CHECKLIST

Definition and Classification

Osteomyelitis is an intraosseous infection with bacteria or, rarely, fungi. It is classified as acute, subacute, or chronic. Acute osteomyelitis is of recent onset and short duration. It is most often hematogenous in origin but may result from trauma such as a compound fracture or puncture wound. It can be metaphyseal, epiphyseal, or diaphyseal in location. Subacute osteomyelitis is of longer duration and is usually caused by less virulent organisms. Chronic osteomyelitis results from ineffective treatment of acute osteomyelitis and is characterized by necrosis and sequestration of bone.