Infections of the skin and soft tissue

Question 1

What are the 2 pathogeneses of skin infection?

Answer 1

1) Localised - inoculation, other route of infection (Eg. neuronal migration)
2) Systemic/ geenralised eg. chicken pox

Question 2

Which 2 herpes viruses can cause skin infection?

Answer 2

1) Herpes simplex virus

2) Varicella zoster virus

Question 3

In addition to the herpes viruses, give 4 other viruses which can cause skin or soft tissue infections?

Answer 3

1) Molluscum contagiosum
2) HPV
3) Orf
4) Cowpox

Question 4

What are the 4 steps in the pathogenesis of herpes simplex?

Answer 4

1) Vesicle formation followed by ulceration and release of vesicle fluid containing infective particles
2) Virus gains entry via sensory nerve endings and migrates along nerve to dorsal root ganglion
3) Latent infection DNA exists as epsiomes and no virus encoded proteins are produced to stimulate an immune response
4) In reactivation is it believed the virus particles migrate outwards to sensory nerve endings and cause clinical manifestations of infection

Question 5

What are the 2 possible histories of a herpes simplex patient?

Answer 5

1) Triggered - eg by infection or stress

2) Preceded by tingling

Question 6

Primary herpes simplex tends to be seen in infants, what would be found on examination?

Answer 6

Extensive, painful lesions

Inside mouth

Question 7

Lesions found in the mouth tend to be caused by which HSV?

Answer 7

HSV2 - mainly genital infections

Question 8

Secondary HSV infections are seen in all ages, what tends to be found on examination?

Answer 8

Peri-oral, weeping, vesicular

Question 9

How is a diagnosis of HSV infection made? 2

Answer 9

1) Clinical

2) PCR of vesicular fluid in difficult cases

Question 10

What is the treatment for cold sores caused by HSV?

Answer 10

Topical acyclovir

Question 11

What is the treatment for genital herpes caused by HSV and HSV in the immunosuppressed patient?

Answer 11

Oral acyclovir

Question 12

What are the 2 common histories for a patient with herpes zoster (shingles) infection?

Answer 12

1) Previous chickenpox - latent infection

2) Triggered by physical or emotional insult - preceded by tingling and/or pain

Question 13

What is found on examination of a patient with herpes zoster infection?

Answer 13

Weeping vesicular rash, with dermatomal distribution

Question 14

How is a diagnosis of herpes zoster infection made? 2

Answer 14

1) Clinical

2) PCR of vesicular fluid for difficult cases

Question 15

When should you seek specialist advice about the treatment of herpes zoster? 3

Answer 15

1) Severe widespread rash
2) Severe immunosuppression
3) Multiple dermatomes involved

Question 16

What are the 2 possible treatments for herpes zoster infection?

Answer 16

1) Oral acyclovir/valaciclovir

2) IV acyclovir

Question 17

What is the causative agent for molluscum contagiosum?

Answer 17

Molluscum contagiosum virus - poxvirus

Question 18

What do the lesions in molluscum contagisum look like?

Answer 18

Raised, pearly lesions up to 3mm, umbilicated

Question 19

How is a diagnosis of molluscum contagiosum made?

Answer 19

Clinical

Question 20

Why is no treatment often used in molluscum contagiosum?

Answer 20

Lesions usually disappear in 6-18 months

Question 21

Although the lesions are self limiting, what 2 treatments can be used in molluscum contagiosum?

Answer 21

Physical treatments

Various topical preparations

Question 22

What are the 2 main causative agents of bacterial infections of the skin and soft tissues?

Answer 22

1) Staph aureus

2) Group A beta haemolytic streptococci (S Pyogenes)

Question 23

In addition to staph aureus and strep pyogenes, give the 3 other bacteria which can cause skin and soft tissue infections?

Answer 23

1) H influenza
2) Pasteurella multocida
3) Enteric organisms

Question 24

Is staph aureus gram positive or negative?

Answer 24

Gram positive

Question 25

Staph aureus is part of what normal flora?

Answer 25

Nasal flora

Question 26

Is s pyogenes gram positive or negative?

Answer 26

Gram positive

Question 27

How do staph aureus and s pyogenes cause disease?

Answer 27

S aureus produces many virulence factors and exotoxins | S pyogenes produces many virulence factors

Question 28

What is impetigo?

Answer 28

Infection of epidermis

Question 29

What are the 2 causative agents in impetigo?

Answer 29

S aureus or s pyogenes or both

Question 30

Where does impetigo often occur?

Answer 30

At sights of skin damage

Question 31

What do the lesions look like in impetigo?

Answer 31

Plaque like lesions with a yellowish exudate - honey crusted lesions

Question 32

How is a diagnosis of impetigo made? 2

Answer 32

1) Clinical diagnosis | 2) Bacterial culture

Question 33

Complications or impetigo are caused by the production of what?

Answer 33

Epidermolytic toxin production (ETA and ETB)

Question 34

What is the one localised and one systemic manifestation of the complications of impetigo?

Answer 34

Localised: Bullous impetigo Systemic: Staphylococci scalded skin syndrome (SSSS)

Question 35

How do epidermolytic toxins ETA and ETB cause the complications of impetigo?

Answer 35

Inactivate a protein called desmosomal glycoprotein desmoglein 1 which is required fro cell-cell adhesion in the superficial epidermis

Question 36

What is erysipelas?

Answer 36

Infection of the dermis

Question 37

What is the causative agent of erysipelas?

Answer 37

S pyogenes

Question 38

Where does erysipelas normally occur and what is is preceded by?

Answer 38

At the sight of skin damage Predominantly the face or shin Preceded by pain and tenderness

Question 39

What 3 things would be found on examination in erysipelas?

Answer 39

1) Fever and malaise 2) Well demarcated inflamed lesion - red, swollen, painful, hot 3) Lymph node enlargement

Question 40

How is a diagnosis of erysipelas made? 2

Answer 40

1) Clinical | 2) Culture rarely helpful

Question 41

What is cellulitis?

Answer 41

Infection of the skin and subcut tissue

Question 42

What are the 4 possible causative agents of cellulitis?

Answer 42

1) S aureus 2) S pyogenes 3) Pasteurella multocida (animal bites) 4) H Influenza

Question 43

Where does cellulitis normally occur?

Answer 43

At a site of skin penetration - can be any part of the body although a portal may not be apparent

Question 44

What 2 things are found on examination in cellulitis?

Answer 44

1) Fever and malaise | 2) Diffuse inflamed lesion (erythema, swelling, tenderness, heat)

Question 45

As there are a range of differential diagnoses for the symptoms of cellulitis, microbiology is often involved in diagnosis, what 3 kinds of samples can be used?

Answer 45

1) Lesions swabs 2) Lesion aspirates and skin biopsy 3) Blood cultures

Question 46

Anthrax is caused by which bacteria?

Answer 46

Bacillus anthracis

Question 47

Bacillus anthracis is acquired from where?

Answer 47

Imported wool, hair and animal hides

Question 48

How does bacillus anthracis enter the body?

Answer 48

Innoculation through breaks in the skin

Question 49

What are the 2 contemporary risk factors for anthrax?

Answer 49

1) Exposure to imported west African drum skins | 2) Injecting drug use

Question 50

What are the patterns of disease of anthrax, what is the prognosis in each?

Answer 50

1) Cutaneous anthrax - readily treated | 2) Inhalational/ septicaemic anthrax - high mortality

Question 51

What is necrotising fasciitis?

Answer 51

Infection of skin and subcutaneous tissue

Question 52

What are the causative agents for type 1 necrotising fasciitis?

Answer 52

Polymicrobial - enteric gram negative bacilli, anaerobes

Question 53

What is the causative agent for type 2 necrotising fasciitis?

Answer 53

S pyogenes

Question 54

Perineal necrotising fasciitis is sometimes referred to as what?

Answer 54

Fournier's or synergistic gangrene

Question 55

Necrotising fasciitis commonly occurs where?

Answer 55

Can be any sight of the body, can be spontaneous or at sight of skin penetration

Question 56

What 2 things are found on examination in NF?

Answer 56

1) Fever and malaise | 2) Dark, rapidly spreading, necrotic lesion

Question 57

How is a diagnosis of NF made?

Answer 57

Microscopy and culture of debrided material or blood

Question 58

What are the 2 treatments for NF?

Answer 58

1) IV Abx | 2) Surgical debridement

Question 59

Why are anaerobic infections of the skin uncommon?

Answer 59

Ready availability of O2

Question 60

What one soft tissue infection is caused by anaerobic bacteria and what is the causative agent?

Answer 60

Gas gangrene | Clostridium perfringens

Question 61

How does gas gangrene appear?

Answer 61

Similar to NF with palpable subcut gas

Question 62

When does gas gangrene more commonly occurs?

Answer 62

Usually a post operative surgical infection

Question 63

What are the 2 treatments for gas gangrene?

Answer 63

1) IV Abx | 2) Surgical debridement

Question 64

As most infections are caused by s aureus or s pyogenes, what is the first line empiric therapy?

Answer 64

Flucoxacillin

Question 65

What 2 Abx are the empiric therapy for NF?

Answer 65

Meropenem and clindamycin

Question 66

If a patient is high risk for MRSA infection (ie. had it previously) what 2 Abx should be used?

Answer 66

Vancomycin, linezolid

Question 67

Which empiric therapy is used in anaerobic infections?

Answer 67

Metronidazole

Question 68

What are the 2 causative organisms of dermatophyte infections?

Answer 68

Dermatophyte fungi: 1) Tricophyton spp. 2) Microsporum spp.

Question 69

Give 3 dermatophyte infections of the skin?

Answer 69

1) Tinea corporis 2) Tinea pedis 3) Tinea cruris

Question 70

Give a dermatophyte infection of the nails?

Answer 70

Onychomycosis

Question 71

Give a dermatophyte infection of the scalp?

Answer 71

Tinea capitis

Question 72

Dermatophyte infections are usually restricted to what part of the skin?

Answer 72

Stratum corneum - rarely penetrate the living cells of the epidermis

Question 73

What do dermatophytes use as nutritional substrate?

Answer 73

Keratin

Question 74

How is a diagnosis of dermatophyte infection made?

Answer 74

Skin scrapings - microscopy and culture (to exclude other conditions such as psoriasis)

Question 75

What is the treatment for dermatophyte infections?

Answer 75

Topical or systemic antifungal agents - depending on sight and extent of infection

Question 76

Which 2 antifungal agents are used in topical therapy in skin infections?

Answer 76

Clotrimazole | Terbinafine

Question 77

What 3 antifungal agents are used as systemic therapy in scalp and nail infections?

Answer 77

Terbinafine Itraconazole Griseofulvin