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

Question 1

Learning Outcomes (for general perusal)

Answer 1

• 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.

Question 2

What this lecture covers

Answer 2

• Skin & soft tissue infections- anatomical classification
• Staphylococcal and streptococcal skin infections
• Leprosy
• Fungal infections of skin
• Infections of muscles, joints and bones

Question 3

What are the three lines of invasion/damage?

Answer 3

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

Question 4

Skin & soft tissue infections - anatomical classification

give examples of the following

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

Answer 4

1. Boils –hair follicles

Carbuncles- hair follicles

2. Impetigo- epidermis

Erysipelas- dermis

Cellulitis- sub cutaneous

3. Necrotizing fasciitis –fascia

Myonecrosis –muscle

Question 5

Where do the following originate/affect?

1. Boils
2. Carbuncles
3. Impetigo
4. Erysipelas
5. Cellulitis
6. Necrotizing fasciitis
7. Myonecrosis

Answer 5

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

Question 6

Skin and Soft Tissue Infections

What are the most common causes?

Answer 6

Staph. aureus → the more common pathogen

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

Question 7

Staph. Aureus

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

Answer 7

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

Question 8

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?

Answer 8

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

Question 9

Describe the pathogenesis of an Abscess

Answer 9

(Pain –redness – swelling)

↓

Infection in & around hair follicle

↓

Organism multiply

↓

Influx of neutrophils

↓

Fibrin is deposited (walled off)

Question 10

Give examples of Staphylococcal Skin Infections

Answer 10

Foliculitis

Scalded Skin Syndrome

Toxic Shock Syndrome

Question 11

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?

Answer 11

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

Question 12

Panton-Valentine leukocidin (PVL)

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

Answer 12

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.

Question 13

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?

Answer 13

1. clinical grounds
2. Culture and further investigation
3. pus / infected tissue / blood
4. Gram stain and culture

Question 14

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?

Answer 14

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)

Question 15

Staph aureus

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

Answer 15

For MSSA (sensitive) = Flucloxicillin

For MRSA (resistant) = Vancomicin

Question 16

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?

Answer 16

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

Question 17

Streptococcal skin infections

Outline the three main groups

How are these usually diagnosed and treated?

Answer 17

• 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

Question 18

Streptococcal skin infections

Describe the appearance of the following:

1. Impetigo
2. Erysipelas
3. Cellulitis

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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?

Answer 20

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

Question 21

Muscle infections

Necrotising fasciitis can involve muscle

Which organisms is Viral Myositis especially associated with?

Describe the course of this condition

Answer 21

Enteroviruses, Influenza

Largely self-limiting

Question 22

Leprosy

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?

Answer 22

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

Question 23

Fugal infections of skin-
clinical classification

Name the different types of mycoses and give examples

Answer 23

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

Question 24

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?

Answer 24

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

Question 25

**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

Answer 25

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 6. TINEA CORPORIS TINEA PEDIS (Athlete's Foot) TINEA UNGUIUM TINEA CAPITIS 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

Question 26

**Dermatophyte Infections** 1. Describe the diagnosis? 2. What is the treatment?

Answer 26

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

Question 27

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

Answer 27

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.

Question 28

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

Answer 28

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

Question 29

Who is at increased risk of **septic athritis**?

Answer 29

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

Question 30

What are the symptoms of **septic arthritis**?

Answer 30

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

Question 31

**Septic Arthritis** ## Footnote How does a microbiological lab diagnosis come about?

Answer 31

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

Question 32

What is the treatment for **septic arthritis**? How long for?

Answer 32

Typically **Flucloxicillin for MSSA** **4-6 weeks antibiotics**

Question 33

**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?

Answer 33

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

Question 34

**4 common skin and soft tissue infections** What are the following caused by? 1. Impetigo 2. Erysipelas 3. Cellulitis 4. Boils, styles, carbuncles

Answer 34

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

Question 35

**Case** 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?

Answer 35

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

Question 36

**Osteomyelitis** 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?

Answer 36

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