3/2/99

Pathology II

 

Pyogenic Osteomelitis

·        Organisms reach bone by:

1.  Hematogenous dissemination

2.  Direct extension from a focus of acute infection in the adjacent joint of soft tissue

3.traumatic implantation after compound fractures or orthopedic surgical procedures

·        Acute Osteomyelitis

Intense infection at site of invasion

·        Necrosis of bone w/in a few days

·        Increase pressure in marrow cavity-compresses vascular spaces

·        High [] of enzymes, toxins from acute inflammatory response

·        Infection spreads through bone to periosteum

·        Subperiosteal abscesses

·        Periosteal detachment may disrupt blood supply and further necrosis

·        Soft tissue extension produces draining sinuses

·        Joints are less affected in adults due to tighter attachment of periosteum

·        Can cross over the joint to fuse a joint

·        A tumor tends to stay in the same bone that it started in

·        Fig 21-02b.  Brodie's abscess

 

Chronic Osteomyelitis

·        Persistence of viable organisms in bone-may have draining sinuses open to the skin

·        Sequestrum-residual necrotic bone is surrounded by a rim of new bone-Involucrum

·        Brodie's abscess-well defined rim of sclerotic bone surrounding a residual abscess

·        Osteopenia—loss of bone density

 

Clinical Features

·        Initial stages-systemic manifestations of infection—fever, malaise, leukocytosis

·        Local signs include:  pain, swelling, redness

·        Bone destruction first noted on radioncuclide scans

·        Vigorous, prolonged antimicrobial therapy

·        Surgical debridement

·        Development of chronic Osteomyelitis may occur if diagnosis is delayed or if Tx is not sufficiently aggressive

·        Complications

·        Pathological fractures

·        Bacteremia

·        Endocarditis

·        Reactive systemic amyloidosis

·        Only in some can they id the bacteria causing the infection—difficult to pick a antibiotic to fight the infection

·        Sqamous cell carcinoma

 

TB Osteomyelitis

·        Bone infection seen in 1-3% of pulmonary TB

·        Hematogenous spread is most common

·        Long bones and vertebrae-favored sites

·        Synoivum is initial site-due to higher o2 pressure (tubercle bacillus requires high [O2]

·        Epiphyseal spread-causes granulomatous reaction w/caseous necrosis and extensive bone destruction

·        Pott's disease-TB of vertebral bodies

·        Vertebral collapse and neurological deficits

·        "cold abscess"—extension into soft tissues—psoas muscle is common site

·        Salmonella and sickle cell anemia patients

 

Page's Disease (Osteitis Deformans)

·        Localized, frenzied osteoclastic activity and bone resorption, followed by exuberant bone formation

·        Produces skeletal deformity from excessive amounts of architecturally abnormal unstable bone

·        Three phases

1. primary phase—initial osteoclastic activity, hypervascularity in marrow and bone loss
2. mixed phase—osteoclastic and osteoblastic proliferation (acid &/or alkaline phosphatase)
3. osteosclerotic phase—dense mineralized bone

·        uncommon before age 40 (3-4% of population)

·        mostly in men

·        predisposing factor for Osteogenic Sarcoma

Pathogenesis

·        may be infectious-slow viral infection

·        paramyxovirus

·        virus induces synthesis of IL-6 ® activates osteoclasts causing bone resorption

·        osteoblastic activity may be reaction to osteolysis

Morphology

·        monostatic (solitary lesion in 10% of cases) or polyostatic (multifocal)

·        spine, skull, pelvic bones-esp common

·        primary phase-extensive resorption of bone

·        mixed phase-combination of bone resorption and new bone formation

·        osteosclerotic phase-new bone lacks lamellar architecture – woven bone-substantial thickening of both cortical an trabecular bone

·        erratic pattern looks like jigsaw puzzle-Mosaic pattern

·        Mosaic pattern of bone deposition is virtually pathognomonic of Paget's disease

·        Abnormally dense, but weaker than usual bone - prone to deformity and fracture

·        Fig 21-3—corn flake appearance

 

Clinical

·        Usually asymptomatic-discovered incidentally on x-ray, or w/ elevation of alkaline phosphatase (osteoblastic activity)

·        Skull enlargement-headache, visual disturbances, deafness

·        Back pain is common-vertebral fractures and spinal root compression

·        Long bones of leg-deformities from weight bearing

·        Transverse fractures of brittle long bones-chalkstick fractures

·        1% develop osteogenic sarcoma

 

Bone tumors

·        1° bone tumors less common than metastatic lesions

·        bone metastasis sites-in order:

·        prostate, breast lung, kidney, GI tract, thyroid

·        metastatic lesions may be osteolytic or osteoblastic or both

·        fig 21-4ii

·        tumors of bone (table 21-2)

·        bone forming-benign

·        osteoma

·        osteoid osteoma

·        osteoblastoma