Myositis Flashcards
What is myositis
• how common are infections of the muscle?
Inflammation in the muscles
• Infections of the muscel are rare
What are 2 ways that bacteria are able to inflitrate the muscle?
- Contiguous sites of infection (skin/subcutaneous abscesses, penetrating wounds, decubitus ulcers, osteomyelitis)
- Hematogenous spread from a different focus
Pyomyositis
• what is it?
• What is the most common cause/
Pyomyositis:
• Bacterial infection of the muscle most commonly caused by Staph aureus and causes pus fomation in the muscle
What clinical characterisitics would you expect someone with pyomyositis to present with?
• how does this differ from someone with osteomyelitis or septic arthritis?
These people present with fever, localized muscle pain, Stiffness, swelling and tenderness.
***While osteomyelitis and septic arthritis may be characterized by fever in some cases (TB in osteomyelitis, etc.) it is not a defining clinical feature***
What is a predisposing factor for bacteremic spread to skeletal muscle?
• Living in the tropics
What infections is pyomyositis typically secondary to?
Typically is secondary to Skin or Bone infection
What areas are typically involved with pyomyositis?
Pyomyositis typically manifests in large muscles of the lower extremity, shoulders, and thorax.
Pyomyositis:
• Pathogenesis
• What are some clinical features of pyomyositis?
• What happens if you miss the diagnosis?
Pathogenesis:
• Previous bacteremia, commonly asymptomatic and transient along with (likely) some minor muscle trauma or injury
Clinically:
• Muscle is very tender with swelling and warmth in the overlying skin. You can aspirate pus.
• If you miss the diagnosis sepsis can develop with striking erythema, exquisite tenderness and fluctuance.
What are the two most common causes of pyomyositis?
- Staph aureus (60-70% of cases)
- Group A strep (1-5%)
How do you diagnose Pyomyositis?
• 3 options
- *Prompt Imaging** is essential:
- *• X-rays** may show presence of swelling or gas in soft tissues
- *• Ultrasound** may show focal abscess formation
- *• MRI is best** - it identifies focal muscle edema and localizes the presence of focal abscesses
How do you treat pyomyositis?
- *1. Drain the abscesses**
- *2. Intiate antibiotic therapy with VANCOMYCIN** - b/c you’re infection is almoster certainly gram + (SA or GAS)
What is the cause of gas gangrene?
• Clostridium perfringes - remember this can also cause food poisoning
Clostridium perfringens
• where does it live?
• What does it look like in culture on blood agar? Reason?
• Gram Stain
Where:
• Lives in the soil in spores
• Vegetative cells are normal flora in the colon and vagina
Blood Agar:
• DOUBLE zone of hemolysis - this is seen as a result of the alpha toxin that damages cell membranes and causes RBC hemolysis
Gram Stain:
• Gram Positive Rods (box car cells)
Clostridium perfringens:
• how does it present?
• Key clinical features?
• Chances of this killing you?
Pain, edema, cellulitis, and gangrene (necrosis) are presence often with Crepitus present due to the formation of gas by this bug (because its an obligate anaerobe). HEMOLYSIS is common (as a result of alpha toxin).
• SHOCK AND DEATH are highly associated with this bug (HIGH MORTALITY)
Clostridium perfringens
• how do you make the diagnosis official?
• Explain in detail.
You must:
- Gram stain => Gram Positive Rods (spores not typically seen)
- Culture organisms anaerobically then identify them by sugar fermentation rxns and Lactic acid production
- DOUBLE zone of hemolysis will be seen on blood agar.
