Bone - Bacterial osteomyelitis (acute)

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Osteomyelitis

Bacterial osteomyelitis (acute)

Reviewers: Dariusz Borys, M.D. (see Reviewers page)
Revised: 7 June 2012, last major update June 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Rare due to use of antibiotics
● Usually pyogenic
● Designated as acute, subacute or chronic, based on clinical duration of disease
● Chronic osteomyelitis: develops in 15-30% due to delayed treatment, inadequate antibiotics, incomplete surgical debridement of necrotic bone, weakened host defenses
● May develop sinus tract lined by squamous epithelium that forms large epidermal inclusion cyst within bone; rarely transforms to well differentiated squamous cell carcinoma with excellent prognosis

Sclerosing osteomyelitis of Garré:
● In jaw, associated with extensive new bone formation that obscures underlying osseous structure
● Also called periostitis ossificans (J Craniofac Surg 2002;13:765)

Brodie abscess:
● Small intraosseous abscess in cortex, walled off by reactive bone with no periosteal reaction
● Cavity may contain infectious organisms or be sterile
● May have late recrudescence
● Therapy: total surgical excision (Tunis Med 2007;85:857)

Pathophysiology
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● Bacteria proliferate in bone, cause inflammation and necrosis
● Spread along haversian system or medullary cavity within shaft and to periosteum
● Subperiosteal abscesses impair blood supply, which causes more necrosis and often draining sinuses

Sequestrum
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● Dead piece of bone
● Gradually separated from living bone by granulation tissue
● May pass through sinus tract
● Avascular and dense on Xray
● Involucrum: sleeve of living tissue created by periosteum which is deposited around sequestrum

Hematogenous spread
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● Most common cause
● Usually metaphyseal in children and adults
● Usually long tubular bones of children; involvement of flat bones is more common in adults

Direct extension
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● Less common
● May be associated with trauma or rarely iatrogenic implantation of infectious material
● In elderly, may affect vertebral column
● May be associated with systemic urinary tract infection, diabetes (affects small bones in feet)
● In younger adults, associated with immunodeficiency or intravenous drug abuse

Type of bacteria
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● 50% of cases are due to unknown bacteria
● 80% of cases with known organisms are due to Staphylococcus aureus, which produces receptors to bone matrix components
● Sickle cell patients may have infections by Salmonella choleraesuis, S. paratyphi B and S. typhimurium
● Neonates are prone to Treponema (periostitis), gram negative rods, Group B Streptococci, Hemophilus influenzae and Listeria species
● Intravenous drug addicts (affecting clavicle, sternoclavicular joint, spine or pelvis): Staphylococcus aureus and coagulase-negative Staphylococcus (Clin Orthop Relat Res 2010;468:2107)
● Post-traumatic cases: Pseudomonas and mixed bacteria
● Other known organisms are E. coli, Pseudomonas and Klebsiella
● Rarely associated with malakoplakia

Sites
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● In children, at areas of rapid growth or increased risk of trauma (distal and proximal femur, proximal tibia and humerus, distal radius)

Radiology description
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● May be negative early
● Three phase bone scans (with Gallium or Indium scanning), MRI or other studies may be necessary
● Late images show prominent periosteal reaction resembling neoplasm

Sclerosing osteomyelitis of Garré:
● Lytic bone destruction surrounded by sclerosis
● Chronic disease may resemble malignant bone tumor due to destructive and regenerative bone changes

Treatment
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● Surgery to remove dead bone (sequestrum)
● Antibiotics; levels in bone may be lower than serum; often Cloxacillin, Nafcillin, third generation cephalosporins; guided by culture and sensitivity reports and drug minimum inhibitory concentration

Case reports
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● 17 month old immunocompetent black girl with disseminated Mycobacterium avium disease (Hum Pathol 1980;11:476)

Gross description
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Varies with patient age:
● Infants under age 1 year often have permanent joint and epiphyseal damage sparing metaphysis and diaphysis
● Children 1 year and older have opposite changes (sparing of joint, damage to metaphysis)
● Adults have joint infection and extensive bone involvement
● Acute disease has pus tracking through bone, periosteal elevation and shell of reactive periosteal bone around necrotic center
● Neonates may have considerable subperiosteal spread
● Chronic disease is accompanied by prominent periosteal bone formation

Micro description
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● Neutrophils (may persist for weeks), lymphocytes and plasma cells with bone necrosis and reactive new bone formation
● Capillary proliferation and fibrosis
● Subtypes include plasma cell osteomyelitis and xanthogranulomatous osteomyelitis (abundant foamy macrophages)
● Bone marrow space replaced by inflammatory tissue
● Salmonella infection may produce tuberculoid granules with variable central necrosis (Am J Surg Pathol 1985;9:531)

Micro images
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Lactobacillus sepsis and osteomyelitis




Osteomyelitis secondary to direct extension of soft tissue infection

Virtual Slides
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Osteomyelitis

End of Bone > Osteomyelitis > Bacterial osteomyelitis (acute)

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