(62) Skin and soft tissue infections Flashcards
1
Q
Name the 4 layers in all epidermis
A
- stratum basale
- stratum spinosum
- stratum granulosum
- stratum corneum
2
Q
What are the functions of the skin?
A
- physical barrier (chemical, UV, micro-organisms)
- homeostasis (thermoregulation, prevention of desiccation electrolyte loss)
- immunological function (Ag presentation and phagocytosis, Langerhans cells, lymphocytes, mononuclear phagocytic cells)
3
Q
Which bacteria colonise the skin?
A
- coagulase-negative staphylococci
- staph. aureus
- propionibacterium
- corynebacterium spp.
4
Q
Give an example of local infection by inoculation
A
- penetration of skin with contaminated object (rusty nail, knife, surgical procedure, injection etc)
- contamination of pre-existing breach in skin surface (abrasion, athletes foot lesion etc)
5
Q
Give an example of how else a localised infection might be caused (other than inoculation)
A
Neuronal migration in herpes simplex
6
Q
Give 2 examples of systemic/generalised infection
A
- chickenpox
- meningococcal sepsis
7
Q
Name viruses that can cause skin/soft tissue infections
A
- herpes viruses (HSV and VZV)
- molluscum contagiosum
8
Q
Describe the pathogenesis of herpes simplex
A
- vesicle formation followed by ulceration and release of vesicle fluid containing infective particles
- virus gains entry via sensory nerve endings and migrates along nerve to DRG
- in latent infection, viral DNA exists as “episomes” and no virus-coded proteins are present to stimulate immune response
- in reactivation, virus particles migrate outwards to sensory nerve endings and cause clinical manifestations of infection
9
Q
Describe the history in herpes simplex infection
A
- triggered by infection or stress etc
- preceded by tingling
10
Q
Describe examination findings in herpes simplex infection
A
- primary infection (infants) = extensive, painful lesion, inside mouth (HSV2 = mainly genital infections)
- secondary infection (all ages) = peri-oral (genitals), weeping, vesicular
11
Q
How is herpes simplex diagnosed?
A
- clinical
- difficult cases: vesicle fluid (PCR for herpes virus DNA)
12
Q
How is herpes simplex treated?
A
- cold sores = topical acyclovir
- genital herpes, immunosuppressed patient = oral acyclovir
13
Q
Describe the history in herpes zoster (shingles)
A
- previous chicken pox (“latent” infection)
- triggered by physical or emotional insult (proceded by tingling and/or pain)
14
Q
Describe the examination findings in herpes zoster (shingles)
A
- weeping, vesicular rash
- dermatomal distribution
15
Q
How is herpes zoster (shingles) diagnosed?
A
- clinical
- difficult cases: vesicle fluid (PCR for herpes virus DNA)
16
Q
How is herpes zoster (shingles) diagnosed?
A
- oral aciclovir/valaciclovir
- IV aciclovir (depending on age, immune status, severity of shingles)
- specialist advice if severe/widespread rash, severe immunosuppression or multiple dermatomes involved
17
Q
What is the causative agent in molluscum contagiosum?
A
Molluscum contagiosum virus (a DNA poxvirus)
18
Q
What is seen on examination in molluscum contagiosum?
A
- raised, pearly lesions up to 3mm
- umbilicate
19
Q
How is molluscum contagiosum diagnosed?
A
Clinical
20
Q
How is molluscum contagiosum treated?
A
- none (lesions usually disappear in 6-18 months)
- various topical preparations
- physical treatments (cryotherapy, diathermy, laser therapy)
21
Q
What is cryotherapy?
A
The application of extreme cold to destroy abnormal or diseased tissue - used to treat a number of diseases especially skin conditions like warts, moles, skin tags and solar keratoses
22
Q
What is diathermy?
A
High-frequency electric current is delivered via shortwave, microwave, or ultrasound to generate deep heat in body tissue
23
Q
Name 6 bacterial skin infections
A
- impetigo
- erysipelas
- cellulitis
- necrotising fasciitis
- gas gangrene
- anthrax
24
Q
What are the causative agents in bacterial skin infections?
A
- mainly staph. aureus and group A b-haemolytic streptococci (S. pyogenes)
- a few others eg. haemophilus influenzae, pasteurella multocida, enteric organisms etc.
25
Describe the features of S. aureus
- gram-positive cocci in clusters
- catalase-positive
- normal nasal flora in approx 30%
- large number of virulence factors eg. DNase, coagulase, teichoic acid
- exotoxin production
26
What are the exotoxins that S. aureus produces?
- epidermolytic toxins A and B (ETA and ETB)
- toxic shock syndrome toxin (TSST-1)
- Panton-Valentin leukocidin (PVL)
27
Describe the features of S. pyogenes
- gram-positive cocci in chains
- catalase-negative
- expresses many virulence factors
28
What are the virulence factors that S. pyogenes expresses?
- adhesins
- M proteins (antiphagocytic)
- hyaluronic acid capsule (antiphagocytic)
- hyaluronidase (facilitates interstitial spread)
- C5a peptidase (anticomplementary)
- streptolysins-O and -S (lysis of red and white blood cells)
- pyrogenic exotoxins
29
What is impetigo?
Infection of epidermis (superficial) - a common and highly contagious skin infection that causes sores and blisters
30
What are the causative agents in impetigo?
- S. aureus
- S. pyogenes
- both
31
Describe the history in impetigo
- occurs at site of skin damage (cut, graze, insect bite, chicken pox, molluscum contagiosum lesion)
- contacts
32
What is seen on examination in impetigo?
- plaque-like lesions
- yellowish exudate
- thick scabs "honey crusted lesions"
33
How is impetigo diagnosed?
- clinical
| - bacterial culture (sensitivity testing may be useful)
34
What are the complications associated with impetigo?
Epidermolytic toxic production (ETA and ETB)
- localised = bullous impetigo
- generalised = staphylococcal scalded skin syndrome (SSSS)
35
A complication of impetigo is SSSS due to ETA and ETB production. Describe the pathogenesis
Desmosomal glycoprotein desmoglein-1 is required for cell-cell adhesion in the superficial epidermis
= inactivated by ETA and ETB
36
What is erysipelas?
Infection of dermis - infection of the upper dermis and superficial lymphatics, usually caused by beta-hemolytic group A Streptococcus bacteria on scratches or otherwise infected areas - more superficial than cellulitis, and is typically more raised and demarcated
37
What is causative agent of erysipelas?
S. pyogenes
38
Describe the presenting history in erysipelas
- often occurs at sites of skin damage
- predominantly face or shin
- proceded by pain and tenderness
39
What is seen on examination in erysipelas?
- fever and malaise
- well-demaractaed inflamed lesion (red, swollen, painful, hot)
- lymph node enlargement
40
How is erysipelas diagnosed?
- clinical
| - culture rarely helpful
41
What is cellulitis?
Infection of skin and subcutaneous tissue - specifically affects the dermis and subcutaneous fat - area of redness which increases in size over a couple of days. The borders of the area of redness are generally not sharp and the skin may be swollen
42
What are the causative agents of cellulitis?
- S. aureus
- S. pyogenes
- pasteurella multocida (animal bites)
- haemophilus influenzae
43
Describe the history in cellulitis
- site of skin penetration (cut, graze, IV catheter, surgical instrument, bite etc)
- any part of body
- portal may not be apparent
44
What is found on examination in cellulitis?
- fever and malaise
| - diffuse inflamed lesion (erythema, swelling, tenderness, heat)
45
How is cellulitis diagnosed?
- clinical
- broad differential diagnosis
- microbiology (lesion swabs, lesion aspirates and skin biopsy, blood cultures)
46
List the features of microbiology diagnostic techniques in cellulitis
Lesion swabs = positive in 85% of cases, swab if lesion is ulcerated
Lesion aspirates and skin biopsy = positive in 10-20%, not recommended routinely
Blood cultures = positive in only 2-4% of cases, use if severe sepsis or systemic signs of infection
47
What are the defining characteristics of stasis dermatitis (differential diagnosis from cellulitis)
- absence of pain or fever
- circumferential
- bilateral
48
What are the defining characteristics of acute arthritis (differential diagnosis from cellulitis)
- involvement of joint
| - pain on movement
49
What are the defining characteristics of pyoderma gangrenosum (differential diagnosis from cellulitis)
- ulcerations on legs
| - history of IBD
50
What are the defining characteristics of hypersensitivity reaction/drug reaction (differential diagnosis from cellulitis)
- exposure to allergen/drug
- pruritus
- absence of fever
- absence of fever or pain
51
What are the defining characteristics of DVT (differential diagnosis from cellulitis)
- absence of skin changes or fever
52
What are the defining characteristics of necrotising fasciitis (differential diagnosis from cellulitis)
- severe pain
- swelling and fever
- rapid progression
- pain out of proportion
- systemic toxicity
- skin crepitus
- necrosis
- ecchymosis
53
What is anthrax?
An infection caused by the bacterium Bacillus anthracis. The skin form presents with a small blister with surrounding swelling that often turns into a painless ulcer with a black center.
54
Which bacteria causes anthrax?
Bacillus anthracis (spore-forming aerobic gram-positive bacillus)
55
How is bacillus anthracis acquired?
From imported wool, hair and animal hides
56
How is a person infected with bacillus anthracis?
Inoculation through breaks in the skin (malignant pustule-eschar, may become septicaemic)
57
Describe the epidemiology of anthrax
- traditionally "woolsorters' disease"
| - contemporary risk factors are exposure to imported (West African) drum skins, and injecting drug use
58
Describe the patterns of disease in anthrax
- cutaneous anthrax = readily treated (mortality less than 1%)
- inhalational/septicaemic anthrax = high mortality (around 45%)
59
What is necrotising fasciitis?
Infection of skin and subcutaneous tissues - commonly known as flesh-eating disease, is a rare infection of the deeper layers of skin and subcutaneous tissues, easily spreading across the fascial plane within the subcutaneous tissue
60
What are the causative agents of necrotising fasciitis?
- type 1 = polymicrobial (enteric gram-negative bacilli and anaerobes)
- type 2 = streptococcus pyogenes
61
Perineal NF is sometimes referred to as what?
- Fournier's
| - synergistic gangrene
62
Describe the history in necrotising fasciitis?
- spontaneous or at site of skin penetration
| - any part of body
63
Describe examination findings in necrotising fasciitis
- fever and malaise
| - dark, rapidly spreading, necrotic lesion
64
How is necrotising fasciitis diagnosed?
- microscopy and culture of debrided material and blood
65
How is necrotising fasciitis treated?
- intravenous antibiotics
| - surgical debridement
66
Why are anaerobic infections of the skin uncommon?
Because of the ready availability of O2
67
Name a skin infection that is caused by an anaerobic bacteria
Gas gangrene
68
What is gas gangrene?
A bacterial infection that produces gas in tissues in gangrene - clinically similar to synergistic gangene (polymicorbial necrotising fasciitis)
- palpable subcutaneous gas
69
Gas gangrene usually happens when?
Usually post-operative surgical site infection
- 'dirty' lower GI procedures
- devitalised tissue eg. amputation
70
What is the causative organism in gas gangrene?
Clostridium perfringens (anaerobic gram-positive bacillus)
71
How is gas gangrene treated?
- intravenous antibiotics
| - surgical debridement
72
What route of treatment is used for bacterial infections?
- depends on disease severity
- topical therapy used for superficial infections only (eg. impetigo, infected grazes etc)
- severe infections e.g cellulitis, necrotising fasciitis etc. are treated with IV antibiotics
73
What empiric therapy is used for most infections (caused by staph. aureus, step. pyogenes)?
- flucloxacillin (fusidic acid or mupirocin for impetigo)
| - penicillin allergy: erythromycin/clarithromycin, vancomycin, linezolid
74
What antibiotics are used for necrotising fasciitis?
(need to cover anaerobes, enterbacteriaceae, streptococci and staphylococci)
- meropenem and clindamycin
75
Give an example of an anti-anaerobic agent
Metronidazole
76
Targeted therapy depends on what?
Culture results
77
What are dermatophytes?
Fungi that require keratin for growth - can cause superficial infections of the skin, hair, and nail
78
What are the dermatophyte infections of the skin?
- tinea corproris
- tinea pedis (athlete's foot)
- tinea curis
79
Name a dermatophyte infection of the nails
Onychomycosis
80
Name a dermatophyte infection of the scalp
Tinea capitis (scalp ringworm, kerion)
81
What are the causative agents of dermatophyte infections?
Dermatophyte fungi
- tricophyton spp. (eg. T. rugrum)
- microsporum spp. (eg. M. canis)
82
Describe the pathogenesis in dermatophyte infections
- dermatophytes use keratin as nutritional substrate
- usually restricted to stratum corneum
- rarely penetrate the living cells of the epidermis
83
How are dermatophytes diagnosed?
Skin scrapings - microscopy and culture (exclude other conditions eg. psoriasis)
84
How are dermatophyte infections treated?
- topical or systemic antifungal agents (depending on site and extent of infection)
85
Name two topical anti fungal therapies used in skin infections
- clotrimazole
| - terbinafine
86
Name three systemic anti fungal therapies used in scalp and nail infections
- terbinafine
- itraconazole
- griseofulvin
