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Clinical Pathology > Skin and soft tissue infections > Flashcards

Skin and soft tissue infections Flashcards

1
Q

What are the main organisms that colonise the skin?

A
  • Coagulase-negative Staphylococci
  • S Aureus
  • Propionibacterium (e.g. Acnes)
  • Corynebacterium
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2
Q

What is the pathogenesis of skin infections?

A

Inoculation

  • penetrate skin with contaminated objects
  • Contamination of pre-existing breach in skin surface

Other route - neuronal migration in herpes simplex

Systemic/generalised infection

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3
Q

What viral infections cause skin infections?

A

Herpes simplex virus

VZV - shingles

Molluscum contagiosum

Cow pox - first virus to be vaccinated

Orf- sheets/goats - purulent producing papule

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4
Q

What is the pathogenesis of the HSV?

A

Vesicle formation -> ulceration -> weeping vesicular lesions (virus release)

Gains entry through sensory nerve endings and remains in dorsal root ganglion

Latent = episome - no immune repose

Reactivation - migrates downward to sensory root ends and manifests

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5
Q

What are the two types of HSV infection

A

Primary - occurs once - usually in infancy, extensive painful lesions in mouth

Secondary - occurs time again - weeping vesicles (peri oral and genital)

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6
Q

What triggers a reactivation infection of HSV?

A

Stress or infection

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7
Q

What is the type of herpes that MAINLY causes a) mouth herpes; b) genital herpes

A

HSV1 (mouth)

HSV2 (genital)

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8
Q

How his herpes simplex virus diagnosed?

A

Clinical usually

Vesicle fluid releases virus (PCR detection of viral DNA)

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9
Q

What is the treatment fora) cold sores and b) genital herpes

A

a) topical acyclovir

b) oral acyclovir

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10
Q

What is the primary and secondary manifestations of VZV

A

a) chicken pox

b) shingles

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11
Q

How does latent infection of VZV present?

A

Shingles - weeping vesicular rash

Dermatome distribution

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12
Q

How is VZV diagnosed?

A

Clinical

Vesicle fluid - PCR VZV DNA

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13
Q

What is the treatment for shingles

A

Acyclovir/valacyclovir - Oral/IV

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14
Q

How does the molluscum contagiosum virus present?

A

Raised PEARLY lesions

Umbilicated

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15
Q

How is molloscum contagious diagnosed?

A

Clinical - very simple

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16
Q

What is the treatment for molloscum contagiosum treated?

A

None - usually disappear with 6-18 months

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17
Q

What are the main causative organisms for bacterial skin infections?

A

Staph Aureus
Strep Pyogenes

Also H influenzae, pasteurella multocida (cat/dogs)

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18
Q

What type of bacteria is staph areus? What exotoxins does it produce that are important in the context of skin infections?

A

Gram positive- normal nasal flora (30% pop)

  • epidermolytic toxin A and B (ETA/ETB)
  • Toxic shock syndrome toxin
  • Paton valentine leucocidin (PVL)
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19
Q

What is the main action of strep pyogenes?

A

Haemolytic

20
Q

What is the causative bacteria that cause impetigo?

A

S aureus

S Pyogenes

21
Q

How does impetigo present?

A

Usually on face (around nose -mainly children) - infection of epidermis

Plaque-like lesions
Yellowish exudate
Thick scabs - honey comb lesions

22
Q

How is impetigo diagnosed?

A

Clinical

Bacterial culture

23
Q

What are the complications of impetigo? What is the pathogenesis?

A

Bullous impetigo

Staphylococcal scalded skin syndrome (SSSS)

Exotoxin - Epidermolytic toxin A&B

24
Q

What area of skin and bodily areas mainly is effected by erysipelas?

A

Dermis

Face and shin

25
Q

What is the causative bacteria for erysipelas?

A

S Pyogenes

26
Q

How does erysipelas present?

A

Lymph node enlargement

Fever and malaise

Well demarcated inflamed lesion - red, swollen, painful, hot

27
Q

What is cellulitis?

A

Infection of the skin and subcutaneous tissue?

28
Q

What are the causative organisms for cellulitis?

A

P Aureus
S Pyogenes
H influenzae
Pasturella multocida (animal bites)

29
Q

How does cellulitis present?

A

Site of inoculation (portal of entry may not be observable!)

Diffuse enlargement - not well demarcated - erythema (redness), swelling, tenderness, hot

Any part of body - UNILATERAL

Fever and malaise

30
Q

How is cellulitis diagnosed?

A
  • Clinical diagnosis
  • Unilateral (discount bilateral differentials)
  • Lesion swabs
  • Blood cultures (rare though)
31
Q

What is the pathogen causing anthrax?

A

Bacillus anthracis

- spore forming aerobic gram positive

32
Q

Where is the source for anthrax?

A

Imported wool, hides, hair, drum skins

33
Q

What is the pathogenesis of anthrax?

A

Inoculation through breaks in the skin

34
Q

How does anthrax present?

A

Malignant pustule

35
Q

When is anthrax lethal?

A

If inhaled/septicaemic

Cutaneous = readily treated

36
Q

What are the two types of necrotising fascitis and what bacteria causes them?

A

Type 1 - polymicrobrial - anaerobes, gram negative bacilli (from large bowel)

Type 2 - strep pyogenes

37
Q

How does necrotising fascitis present?

A

Dark, rapidly spreading necrotising lesion

Fever and malaise (very sick!)

38
Q

What is the treatment of necrotising fascitis?

A

IV antibiotics

Surgical debridement

39
Q

What is the causative organism for gas gangrene?

A

Clostridium perfrinigens - anaerobic gram positive

Dirty lower GI procedures/limb amputation

40
Q

How does gas gangrene present and whats its treatment?

A

Subcutaneous gas
Dark rapidly spreading necrotising

IV antibiotics and limb debridement

41
Q

When should topical/ora/IV antibiotics be used?

A

Topical - superficial infections e.g. impetigo erysipelas

Oral/IV = more severe - cellulitis/necrotising fascitis/gas gangrene etc

42
Q

What is the treatment for staph aureus/strep pyogenes

A

Penecillin (flucloxacillin)

Allergy -erythromycin/calrithromycin vancomycin, linezoid

MRSA - vancomycin, linezoid

43
Q

What antibiotics are used to treat anaerobic infections?

A

Metronidazole

44
Q

What antibiotics should we use for necrotising facilities?

A

Meropenem

Clindamycin

45
Q

What are skin fungal infections referred to as? What is there pathogenisis

A

Dermatophyte infections

Use keratin as nutritional substrate

46
Q

What are the name of dermatophyte infections?

A

Skin

  • Tina corporis
  • Tina pedis (athletes foot)
Scalp
Tina capitus (ring worm)

Clinical Pathology (50 decks)

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