SPR L3 Infections of Skin, Soft Tissue, Muscle, Bone and Joints Flashcards Preview

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Flashcards in SPR L3 Infections of Skin, Soft Tissue, Muscle, Bone and Joints Deck (36):

Learning Outcomes (for general perusal)

•Describe the clinical features of skin & soft tissue infections

•Describe  the principal pathogens in skin & soft tissue infection

•Describe the appropriate specimens & lab diagnosis of skin & soft tissue infection

•Describe the management of skin & soft tissue infection

•Describe infections of muscles, joins and bones. 


What this lecture covers

•Skin & soft tissue infections- anatomical classification

•Staphylococcal and streptococcal skin infections


•Fungal infections of skin

•Infections of muscles, joints and bones


What are the three lines of invasion/damage?

  1. Breach of intact skin- infection of skin
  2. Skin manifestations of systemic infection
  3. Toxin-mediated skin damage 


Skin & soft tissue infections - anatomical classification

give examples of the following

  1. Abcess Formation
  2. Spreading Infections
  3. Necrotizing Infections

  1. Boils –hair follicles

    Carbuncles- hair follicles  

  2. Impetigo- epidermis

    Erysipelas- dermis

    Cellulitis- sub cutaneous 

  3. Necrotizing fasciitis –fascia

    Myonecrosis –muscle 


Where do the following originate/affect?

  1. Boils
  2. Carbuncles
  3. Impetigo

  4. Erysipelas

  5. Cellulitis

  6. Necrotizing fasciitis

  7. Myonecrosis 

  1. Hair follicles
  2. Hair follicles
  3. epidermis
  4. dermis
  5. subcutaneous
  6. fascia
  7. muscles


Skin and Soft Tissue Infections

What are the most common causes?

Staph. aureus   →   the more  common pathogen

Strept. pyogenes → the more rapidly progressive – spreading infection (AKA group A haemolytic streptococcus)


Staph. Aureus 

  1. Describe the appearance of this organism
  2. How is infection acquired?

  1. Gram +ve cocci in clusters, Catalase +ve , coagulase +ve
  2. by 'self-inoculation' from a carrier site or by contact with an exogenous source 


Staphylococcal skin infections
Staph. aureus

  1. Give examples of infection due to focal suppuration
  2. Give examples of infection that is toxin-mediated
  3. What else does it cause?

  1. •Minor skin infections boils, styes and carbuncles

    •More serious skin & soft tissue infections

    Post-operative wound infection

  2. Toxic shock syndrome TSST1 - Especially tampon associated

    Scalded skin syndrome exfoliatin –Especially newborn

  3. Also causes the spreading infections impetigo and cellulitis covered in streptococcal infections 


Describe the pathogenesis of an Abscess

(Pain –redness – swelling)

Infection in & around hair follicle

Organism multiply

Influx of neutrophils

Fibrin is deposited (walled off) 


Give examples of Staphylococcal Skin Infections


Scalded Skin Syndrome

Toxic Shock Syndrome


Methicillin-resistant Staphylococcus aureus (MRSA)

  1. What is it?
  2. What are the latest concerns?
  3. Outline the treatment?
  4. How can MRSA be prevented?

  1. Staph aureus resistant to penicilllinase  resistant penicillins.

  2. Concerns about emergence of CA-MRSA 

  3. Guided by sensitivity - Vancomycin & others

  4. Careful handwashing - Standard precautions for infection control practices 


Panton-Valentine leukocidin (PVL)

  1. What is PVL and what does it cause?
  2. Who does it affect?

  1. PVL is a cytotoxin that destroys white blood cells, causes extensive tissue necrosis and severe infection

  2. Usually associated with community-acquired infections - generally affect previously healthy young children and young adults.


•Still fairly uncommon in UK but increasing

•Both MSSA (most) and MRSA

•Specific national guidance on diagnosis and management.


Diagnosis of staphylococcal skin infections 

  1. What is diagnosis generally made on?
  2. What else is important in hospital infections?
  3. What specimens can be taken?
  4. What will laboratory analysis consist of?

  1. clinical grounds
  2. Culture and further investigation

  3. pus / infected tissue / blood

  4. Gram stain and culture


Treatment of staphylococcal skin infections
How are the following treated?

  1. Minor lesions
  2. severe infection and lesions
  3. recurrent/persistent infections


Why is drainage so important?

  1. drainage
  2. drainage and antibiotics
  3. decolonization (topical antistaphylococcal agent)



pH within abcesses is very low – antibiotics less are less helpful


(antibiotics are acidic)



Staph aureus


Name the key antibiotics involved in the treatment of staph aureus?

For MSSA (sensitive) =  Flucloxicillin

For MRSA (resistant) = Vancomicin


Strept. Pyogenes 

  1. Which cause skin infections?
  2. Describe their appearance
  3. What does the organism produce?
  4. Which types have a predilection for skin?

  1.  Group A - beta hemolytic streptococci (GAS)
  2. Gram-positive cocci in chains
  3. Organism elaborates a number of toxic products & enzymes. Hyaluronidase – tissue spread
  4. Particular M types


Streptococcal skin infections  

Outline the three main groups




How are these usually diagnosed and treated?

  • Pyogenic local infections
    • impetigo
    • AGN may complicate skin infections
  • Invasive diseases
    • Erysipelas - dermis
    • Soft tissue sepsis/cellulitis - subcut
    • Necrotizing  fasciitis
  • Toxigenic
    • Scarlet fever
    • TSS 


Diagnosed clinically and treated with penicillin



Streptococcal skin infections

Describe the appearance of the following:

  1. Impetigo 
  2. Erysipelas
  3. Cellulitis

  1. yellow, crusted lesions- may be mixed with Staph aureus

  2. involving the dermal lymphatics-clearly demarcated area of erythema & induration

  3. acute spreading infection of the skin that involves subcutaneous tissues


4 common skin and soft tissue infections

Name the antibiotic used to treat each of the following:

  1. Impetigo

  2. Erysipelas

  3. Cellulitis

  4. Boils, styles, carbuncles

  1. Oral Fluclixicillin
    1. Add phenoxymethylenicillin if strep suspected (severe) (7 days, clarythromycin if penicillin allergic)
  2. Penicillin
  3. Flucloxicillin* +/- penicillin 
    1. But if MRSA suspected, cover for this
  4. Flucloxicillin


Necrotising Soft-tissue Infection

  1. What is necrotising fasciitis?
    1. How does it spread? Causing what?
    2. What causes it?
  2. What is GAS Gangrene?
    1. What causes it?
    2. What is it associated with?
    3. What treatment is vital?

  1. Infection below the dermis.
    1. Spreads along the fascial planes → disruption of blood supply. "Flesh eating". 

      Severe and rapidly progressive. Death in hours without immediate treatment

    2. Mixed organisms including Strep pyogenes & Anaerobes
  2. Organisms  invade into muscle, cause necrosis and produce  gas bubbles
    1. Cl. perfringens
    2. Follows infection associated with necrosis- trauma/ischaemia
    3. Immediate surgical debridement


Muscle infections

Necrotising fasciitis can involve muscle

Which organisms is Viral Myositis especially associated with?

Describe the course of this condition

Enteroviruses, Influenza

Largely self-limiting



  1. What is it caused by?
  2. How does it spread?
  3. What are the clinical features?
  4. How is it diagnosed?
  5. How is it treated?
  6. Name two types and the difference between them?

  1. Mycobacterium leprae
  2. Requires close & prolonged contact
  3. IP –years- gradual onset. According to CMI response: TL or LL or intermediate. People can’t feel pain in areas. Traumatic damage to deinnervated skin. 
  4. Cannot be grown in-vitro. M. leprae acid-fast rods in nasal scrapings and lesion biopsies
  5. Treated with dapsone  given as part of a multidrug regimen to avoid resistance 
  6. Lepromatous Leprosy and Tuberculoid Leprosy 
    1. Tuberculoid L involves a localised lesion that remains the same for a long time


Fugal infections of skin-
clinical classification 

Name the different types of mycoses and give examples

  • Superficial mycoses eg. Malassezia
  • Cutaneous mycoses eg. dermatophytes & cutaneous candidiasis
  • Subcutaneous mycoses
  • Skin manifestations of systemic mycosis include blastomycosis, cryptococcosis


Pityriasis- tinea versicolor

  1. What is this? What is it caused by?
  2. Where is the infection confined to?
  3. What does it look like?
  4. How is a diagnosis made?
  5. What is the treatment?

  1. Common skin disease caused by overgrowth of  yeast Malassezia

  2. confined to trunk, proximal parts

  3. Hypo or hyper-pigmented macules- not itchy

  4. Diagnosis: direct microscopy of scrapings:

  5. Treatment:

    –Topical azole or

    –Selenium sulphide lotion


Dermatophyte Infections

  1. How does infection come about?
  2. What is the common term?
  3. What are the infectious agents?
  4. What is the method of transmission?
  5. How is diagnosis made?
  6. What different diagnoses can be made?
  7. Describe the macroscopic infection

  1. Filamentous fungi invading keratinized structures : skin, hair & nails 
  2. Ringworm
  3. Epidermophyton, Microsporum &  Trichophyton
  4. Anthropophilic, zoophilic or geophilic
  5. clinically according to site of infection

         TINEA PEDIS (Athlete's Foot)



          TINEA CRURIS (Jock Itch)

          TINEA BARBAE (Barber's Itch)

7. Lesion that has an advancing margin, that tends to be where the maximum inflammation is, within clearing/resolution in the middle


Dermatophyte Infections

  1. Describe the diagnosis?
  2. What is the treatment?

  1. microbiological - direct microscopic examination of scales dissolved in KOH, by culture of scrapings of lesions
  2. Topical & oral antifungal agents


Reactive arthritis

  1. Where does infection occur?
  2. What type of infection is it?
  3. What does it affect?

  1. infection at a distant site
  2. Mainly viral : Erythrovirus B19, Rubella or after some enteric bacteria or Chlamydia infection
    1. Immunologically-mediated
  3. Several joints at once. 


Septic Arthritis

  1. What causes bacteria to localize to joints?
  2. Where does it occur?
  3. What is the commonest causative organism?

  1. after trauma, Haematogenous spread, can occur in prosthetic joints post surgery (Coagulase negative Staph)
  2. Often occurs in one joint
  3. Staph. aureus.


Who is at increased risk of septic athritis?

  • Prosthetic  joints
  • Bacterial infection elsewhere
  • Intravenous (IV) drug use
  • Immunosupression
  • Recent joint injury/surgery


What are the symptoms of septic arthritis?


  • Inability to move the limb with the infected joint (pseudoparalysis)
  • Intense joint pain
  • Joint swelling
  • Joint redness
  • Low fever


Septic Arthritis

How does a microbiological lab diagnosis come about?


  • Aspiration of joint fluid for cell count, gram stain, and culture
  • Blood culture


What is the treatment for septic arthritis?

How long for?

Typically Flucloxicillin for MSSA

4-6 weeks antibiotics



Bone infections- osteomyelitis

  1. What is osteomyelitis?
  2. What is the most common pathogen?
  3. What is the route for spread of infection?
  4. Where does it typically involve?
  5. What are symptoms?
  6. How is a diagnosis made?

  1. Acute or chronic infection of the bone
  2. Staph. aureus
  3. adjacent infection or hematogenous
  4. the growing end of a long bone
  5. Painful tender bone lesion + general febrile illness.
  6. Blood culture, Bone biopsy (in open lesions), Radiologically

Remember, if febrile = BLOOD CULTURE


4 common skin and soft tissue infections

What are the following caused by?

  1. Impetigo
  2. Erysipelas
  3. Cellulitis
  4. Boils, styles, carbuncles


  1. Staph Aureus (or strep pyogenes)
  2. Strep Pygogenes
  3. Strep Pyogenes (or staph aureus)
  4. Staph Aureus



4-year-old boy with a history of a painful arm

  • fell while on a climbing frame 5 days ago
  • lacerated right forearm
  • area around wound was red and  swollen.
  • he has become more unwell in the last 24 hours with fever, and vomiting-
  • On examination, he is miserable, dehydrated and feverish. His right forearm  is tender over the area of the wound
  1. What is the likely diagnosis?
  2. What investigations would you perform?

The results of investigations are hemoglobin 15g/dl and white cell count 24x 109/l with 90% neutrophils, and blood culture grow Staph aureus sensitive to methicillin.

A radiograph of the forearm shows soft tissue swelling over the affected are of the forearm.

  1. How would you treat this condition?

  1. Wound infection – is there an area of cellulitis around the wound?
  2. Swab, get material (ideally pus) from the wound. Is this staph aureus, is it group A strep? Do blood cultures. 


  1. White cell count is raised – bacterial infection. Almost all neutrophils

    Can use flucloxicillin

    Would have him on this antibiotic before the results came 






  1. How is treated?
  2. Give examples
    1. What if the patient is penicillin allergic?
    2. What if the infection is caused by MRSA?
  3. How long for?

  1. Treated with antibiotics and sometimes surgery
  2. Typically Flucloxicillin (+/- fusidic acid or rifampicin) for MSSA
    1. Clindamicin if penicillin allergic
    2. Vancomycin for MRSA
  3. 6 weeks