Musculoskeltal System: Lec.5 - Bacterial Musculoskeletal Infections I

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Musculoskeltal System Lecture 5 Bacterial Musculoskeletal Infections I

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Musculoskeltal System Lecture 5 Bacterial Musculoskeletal Infections I

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5Q:

How do you differentiate necrotizing fasciitis from simple cellulitis?

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-Pain out of proportion to the clinical appearance of the skin affected

-Identify those at increased risk: diabetics, others with abnormal peripheral circulation, immunocompromised (HIV, cancer), traumatic wounds, or surgical incisions

-High fever (104 or higher)

-Toxic appearance (person looks ill)

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5Q:

Pathological features of necrotizing fasciitis

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-Extensive tissue destruction

-Thrombosis of blood vessels

-Abundant bacteria spreading through fascial planes

-In early stages relatively few acute inflammatory cells

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5Q:

Type I NF, who gets it.

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diabetes mellitus, abdominal surgery, perineal infection
Mixed infection: anerobes, anaerobic streptococci, facultative organisms (synergistic nonclostridial myonecrosis)

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5Q:

Type II NF, who gets it.

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Type 2 – Grp A streptococcus (flesh eating strain)
Other etiologies: Aeromonas hydrophilia and Vibrio vulnificus (both are salt water organisms)

likes to get into skin, and has a high concentration of lipase enzyme to invade the tissues.

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5Q:

Presentation of Type I NF

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-Clinically resembles gas gangrene
-Significant gas formation
-Copious seropurulent exudate occurs 3-4 days after injury
-Unpleasant sour odor
-If muscles involved, react to stimulation (differentiate from clostridial myonecrosis)

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5Q:

What does the Gram stain of NF look like?

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Gram stain - numerous streptococci, pleomorphic gram negative rods with many poly’s

Culture usually mixed
Anaerobic streptococci
Group A strep or S. aureus
Often enteric bacteria and Bacteroides

**big mix!

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5Q:

What is a left shift leukocytosis?

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you're seeing more poly morpho nucleocytes and more immature white blood cells. this is a diagnostic aid for NF.

other aids are:
Elevated sedimentation rate
Elevated creatinine phosphokinase
Hypocalcemia
Hypoalbuminemia
*losing protein from the inflamm response.

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5Q:

What causes Type II NF? What other condition has a similar presentation?

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Caused by Grp A streptococcus
Flesh eating strain: due to high amount of lipase enzyme;Secrete superantigens

-Resembles clostridial gas gangrene but no gas formation

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5Q:

Is there gas with Strep Pyogenes NF?

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No, sir, there is not. So check for gas with x-ray or MRI to made that diagnosis.

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5Q:

Few keys points about Aeromonas Hydrophilia Myonecrosis

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Motil gram neg. rod, found in fresh water. it's oxidase positive.

rapid progression from penetrating trauma in freshwater (think fish)

looks like clostridial gas gangrene, and bacteremia is present often.

tx: surgical debridement and antimicrobial therapy.

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5Q:

What type of clostridium is the usual cause for gas gangrene (clostridial myonecrosis)?

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Clostridium perfringens. Gas gangrene is a rapidly progressive, life-threatening, toxemic infection of subcutaneous tissue and skeletal muscle. It's usually due to traumatic injury.

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5Q:

Pathophysiology of Tissue Necrosis

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Break in skin--> Wound contamination with bacteria--> edema and tissue hypoxia --> germination and exotoxin release of bacteria --> necrosis of muscle, fat, subq tissue --> decrease blood flow causes more hypoxia --> liquifaction necrosis of tissue due to enzymes produced by anaerobic bacteria--> back to tissue necrosis step

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5Q:

What does gas gangrene look like?

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foul odor, gas bubbles (crepitus), swollen yellow or white skin around wound, Blebs containing sero-sanguineous fluid develop in overlying skin and areas of green-black cutaneous necrosis appear, muscles doesnt contract b/c of rapid degeneration, sudden onset (2-4 hrs)

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5Q:

What etiology is spontaneous, non-traumatic gas gangrene almost always associated with?

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Clostridium Septicum, and is associated with colon cancer!

presents with bacteremia, pain, and fever. tx like gas gangrene (debride, penicillin G and clindamyacin, hyperbaric oxygen)

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5Q:

Myalgias are prominent features of what?

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Prominant features of a variety of viral infections (influenza, dengue, etc.) and intracellular bacterial infection (Rocky Mountain Spotted Fever)
-likely due to immunologic response.

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5Q:

What is the immune process relating to muscle degradation due to infection?

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Macrophages → IL-1 + TNF → prostaglandin E2
→ muscle protease


Central role played by IL-1 and TNF which leads to increased synthesis in muscle cell lysosomes