Skin & soft tissue infections

Question 1

What is the pathogenesis of skin infections?

Answer 1

• Systemic/generalised infection (chicken pox, meningococcal sepsis)
• Localised infection (inoculation)

Question 2

What viruses cause skin infections?

Answer 2

• Herpes viruses (HSV, VZV)
• HPV
• Orf
• Cowpox
• Molluscum contagiosum

Question 3

What is the pathogenesis of herpes simplex?

Answer 3

• Vesicle formation w/ulceration & release of vesicle fluid containing infective particles
• Gains entry via sensory nerve endings & migrate to dorsal root ganglion
• latent infection viral DNA episomes stimulate immune response

Question 4

What is seen on clinical examination of herpes simplex? How is it treated?

Answer 4

• Extensive painful lesions inside mouth
• Peri-oral(cold sores)/genital herpes
• Weeping, vesicular
• Acyclovir

Question 5

What is seen on a clinical examination of shingles?

Answer 5

• Weeping, vesicular rash
• Dermatomal distribution
• tingling and/or pain

Question 6

What is molluscum contagiosum and its clinical examination?

Answer 6

• Poxvirus
• Raised pearly lesion
• Umbilicated
• laser therapy, cryotyherapy, diathermy

Question 7

What bacterial skin infection are there?

Answer 7

• Impetigo
• Cellulitis
• Necrotising fasciitis
• Anthrax
• Erysipelas
• Gas gangrene

Question 8

How are skin bacterial infections caused?

Answer 8

• Staph aureus

- Group A β-haemolytic streptococci (S. pyogenes)

Question 9

Describe staph aureus

Answer 9

• Gram positive cocci
• Clusters
• Catalase positive
• Exotoxin production
• Virulence factors: DNAse, coagulase, t-acid

Question 10

Describe strep pyogenes

Answer 10

• Gram +ve cocci in chains
• Catalase-negative
• VF: adhesins, M.proteins, hyaluronidase

Question 11

Describe impetigo?

Answer 11

• Infection of epidermis (superficial)
• S.aureus, S.pyogenes
• Plaque like lesions, scabs, yellowish exudate

Question 12

What are complications of impetigo?

Answer 12

• Epidermolytic toxin production (ETA & ETB)
• localised: bullous impetigo
• Generalised: scalded skin syndrome

Question 13

What is erysipelas?

Answer 13

• Infection of dermis
• S.pyogenes
• Preceded by pain & tenderness
• Face or shin

Question 14

What are the clinical examinations for erysipelas?

Answer 14

• Fever & malaise
• inflammed lesion: red, swollen, painful, hot
• Lymph node enlargement

Question 15

Describe cellulitis

Answer 15

• Site of skin penetration
• Fever & malaise
• Diffuse inflamed lesion: swelling, erythema, heat, tenderness

Question 16

How is cellulitis diagnosed?

Answer 16

• lesion swabs positive
• blood cultures
• Skin biopsy

Question 17

What are the defining characteristics of pyoderma gangrenosum?

Answer 17

• Ulceration of legs

- History of inflammatory bowel disease

Question 18

Describe necrotising fasciitis

Answer 18

• Infection of skin & subcut tissue
• Polymicrobial-
  1) anaerobes, gram -ve bacilli, 2)strep pyogenes
• Perineal= synergistic gangrene/fournier’s
• Fever, malaise, dark rapidly spreading necrosis
• D= blood, derided material
• T=IV antibiotics & surgical debridement

Question 19

Describe anthrax

Answer 19

• B.antharcis
• spore forming aerobic gram +ve bacillus
• wool, hair, animal hides
• Woolsorter’s disease
• imported drum skin, injecting drugs
• Malignant pustule, septicaemia, eschar

Question 20

What are anaerobic infections of skin & soft tissue?

Answer 20

• Gas gangrene: palpable subcut gas
• C.perfringens
• IV antibiotics & surgical debridement

Question 21

What antibiotics are best used for:

• Staph aureus
• Penicillin allergy
• Anaerobic infections
• MRSA

Answer 21

• SA: flucloxacillin
• PA: erythromycin
• A: metronidazole
• MRSA: vancomycin

Question 22

What are common dermatophyte infections?

Answer 22

-Skin= tinea corporis, tinea pedis (athletes foot) tinea cruris
-Nails= onychomycosis
-Scalp= scalp ringworm
Cause: T.rubrum, M.canis

Question 23

What is the pathogenesis of fungal infections?

Answer 23

• Dermatophytes use keratin as nutrition

- Restricted to stratum corneum