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Year 2 Clinical Pathology > Infections of the skin and soft tissue > Flashcards

Infections of the skin and soft tissue Flashcards

1
Q

What are the 2 pathogeneses of skin infection?

A

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

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2
Q

Which 2 herpes viruses can cause skin infection?

A

1) Herpes simplex virus

2) Varicella zoster virus

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

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

A

1) Triggered - eg by infection or stress

2) Preceded by tingling

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6
Q

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

A

Extensive, painful lesions

Inside mouth

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7
Q

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

A

HSV2 - mainly genital infections

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8
Q

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

A

Peri-oral, weeping, vesicular

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9
Q

How is a diagnosis of HSV infection made? 2

A

1) Clinical

2) PCR of vesicular fluid in difficult cases

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10
Q

What is the treatment for cold sores caused by HSV?

A

Topical acyclovir

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11
Q

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

A

Oral acyclovir

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12
Q

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

A

1) Previous chickenpox - latent infection

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

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13
Q

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

A

Weeping vesicular rash, with dermatomal distribution

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14
Q

How is a diagnosis of herpes zoster infection made? 2

A

1) Clinical

2) PCR of vesicular fluid for difficult cases

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15
Q

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

A

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

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16
Q

What are the 2 possible treatments for herpes zoster infection?

A

1) Oral acyclovir/valaciclovir

2) IV acyclovir

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17
Q

What is the causative agent for molluscum contagiosum?

A

Molluscum contagiosum virus - poxvirus

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18
Q

What do the lesions in molluscum contagisum look like?

A

Raised, pearly lesions up to 3mm, umbilicated

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19
Q

How is a diagnosis of molluscum contagiosum made?

A

Clinical

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20
Q

Why is no treatment often used in molluscum contagiosum?

A

Lesions usually disappear in 6-18 months

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21
Q

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

A

Physical treatments

Various topical preparations

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22
Q

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

A

1) Staph aureus

2) Group A beta haemolytic streptococci (S Pyogenes)

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23
Q

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

A

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

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24
Q

Is staph aureus gram positive or negative?

A

Gram positive

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25
Q

Staph aureus is part of what normal flora?

A

Nasal flora

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26
Q

Is s pyogenes gram positive or negative?

A

Gram positive

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27
Q

How do staph aureus and s pyogenes cause disease?

A

S aureus produces many virulence factors and exotoxins

S pyogenes produces many virulence factors

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28
Q

What is impetigo?

A

Infection of epidermis

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29
Q

What are the 2 causative agents in impetigo?

A

S aureus or s pyogenes or both

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30
Q

Where does impetigo often occur?

A

At sights of skin damage

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31
Q

What do the lesions look like in impetigo?

A

Plaque like lesions with a yellowish exudate - honey crusted lesions

32
Q

How is a diagnosis of impetigo made? 2

A

1) Clinical diagnosis

2) Bacterial culture

33
Q

Complications or impetigo are caused by the production of what?

A

Epidermolytic toxin production (ETA and ETB)

34
Q

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

A

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

35
Q

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

A

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

36
Q

What is erysipelas?

A

Infection of the dermis

37
Q

What is the causative agent of erysipelas?

A

S pyogenes

38
Q

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

A

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

39
Q

What 3 things would be found on examination in erysipelas?

A

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

40
Q

How is a diagnosis of erysipelas made? 2

A

1) Clinical

2) Culture rarely helpful

41
Q

What is cellulitis?

A

Infection of the skin and subcut tissue

42
Q

What are the 4 possible causative agents of cellulitis?

A

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

43
Q

Where does cellulitis normally occur?

A

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

44
Q

What 2 things are found on examination in cellulitis?

A

1) Fever and malaise

2) Diffuse inflamed lesion (erythema, swelling, tenderness, heat)

45
Q

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?

A

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

46
Q

Anthrax is caused by which bacteria?

A

Bacillus anthracis

47
Q

Bacillus anthracis is acquired from where?

A

Imported wool, hair and animal hides

48
Q

How does bacillus anthracis enter the body?

A

Innoculation through breaks in the skin

49
Q

What are the 2 contemporary risk factors for anthrax?

A

1) Exposure to imported west African drum skins

2) Injecting drug use

50
Q

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

A

1) Cutaneous anthrax - readily treated

2) Inhalational/ septicaemic anthrax - high mortality

51
Q

What is necrotising fasciitis?

A

Infection of skin and subcutaneous tissue

52
Q

What are the causative agents for type 1 necrotising fasciitis?

A

Polymicrobial - enteric gram negative bacilli, anaerobes

53
Q

What is the causative agent for type 2 necrotising fasciitis?

A

S pyogenes

54
Q

Perineal necrotising fasciitis is sometimes referred to as what?

A

Fournier’s or synergistic gangrene

55
Q

Necrotising fasciitis commonly occurs where?

A

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

56
Q

What 2 things are found on examination in NF?

A

1) Fever and malaise

2) Dark, rapidly spreading, necrotic lesion

57
Q

How is a diagnosis of NF made?

A

Microscopy and culture of debrided material or blood

58
Q

What are the 2 treatments for NF?

A

1) IV Abx

2) Surgical debridement

59
Q

Why are anaerobic infections of the skin uncommon?

A

Ready availability of O2

60
Q

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

A

Gas gangrene

Clostridium perfringens

61
Q

How does gas gangrene appear?

A

Similar to NF with palpable subcut gas

62
Q

When does gas gangrene more commonly occurs?

A

Usually a post operative surgical infection

63
Q

What are the 2 treatments for gas gangrene?

A

1) IV Abx

2) Surgical debridement

64
Q

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

A

Flucoxacillin

65
Q

What 2 Abx are the empiric therapy for NF?

A

Meropenem and clindamycin

66
Q

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

A

Vancomycin, linezolid

67
Q

Which empiric therapy is used in anaerobic infections?

A

Metronidazole

68
Q

What are the 2 causative organisms of dermatophyte infections?

A

Dermatophyte fungi:

1) Tricophyton spp.
2) Microsporum spp.

69
Q

Give 3 dermatophyte infections of the skin?

A

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

70
Q

Give a dermatophyte infection of the nails?

A

Onychomycosis

71
Q

Give a dermatophyte infection of the scalp?

A

Tinea capitis

72
Q

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

A

Stratum corneum - rarely penetrate the living cells of the epidermis

73
Q

What do dermatophytes use as nutritional substrate?

A

Keratin

74
Q

How is a diagnosis of dermatophyte infection made?

A

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

75
Q

What is the treatment for dermatophyte infections?

A

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

76
Q

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

A

Clotrimazole

Terbinafine

77
Q

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

A

Terbinafine
Itraconazole
Griseofulvin

Year 2 Clinical Pathology (64 decks)

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