Skin & soft tissue infections Flashcards
What is the pathogenesis of skin infections?
- Systemic/generalised infection (chicken pox, meningococcal sepsis)
- Localised infection (inoculation)
What viruses cause skin infections?
- Herpes viruses (HSV, VZV)
- HPV
- Orf
- Cowpox
- Molluscum contagiosum
What is the pathogenesis of herpes simplex?
- 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
What is seen on clinical examination of herpes simplex? How is it treated?
- Extensive painful lesions inside mouth
- Peri-oral(cold sores)/genital herpes
- Weeping, vesicular
- Acyclovir
What is seen on a clinical examination of shingles?
- Weeping, vesicular rash
- Dermatomal distribution
- tingling and/or pain
What is molluscum contagiosum and its clinical examination?
- Poxvirus
- Raised pearly lesion
- Umbilicated
- laser therapy, cryotyherapy, diathermy
What bacterial skin infection are there?
- Impetigo
- Cellulitis
- Necrotising fasciitis
- Anthrax
- Erysipelas
- Gas gangrene
How are skin bacterial infections caused?
- Staph aureus
- Group A β-haemolytic streptococci (S. pyogenes)
Describe staph aureus
- Gram positive cocci
- Clusters
- Catalase positive
- Exotoxin production
- Virulence factors: DNAse, coagulase, t-acid
Describe strep pyogenes
- Gram +ve cocci in chains
- Catalase-negative
- VF: adhesins, M.proteins, hyaluronidase
Describe impetigo?
- Infection of epidermis (superficial)
- S.aureus, S.pyogenes
- Plaque like lesions, scabs, yellowish exudate
What are complications of impetigo?
- Epidermolytic toxin production (ETA & ETB)
- localised: bullous impetigo
- Generalised: scalded skin syndrome
What is erysipelas?
- Infection of dermis
- S.pyogenes
- Preceded by pain & tenderness
- Face or shin
What are the clinical examinations for erysipelas?
- Fever & malaise
- inflammed lesion: red, swollen, painful, hot
- Lymph node enlargement
Describe cellulitis
- Site of skin penetration
- Fever & malaise
- Diffuse inflamed lesion: swelling, erythema, heat, tenderness
How is cellulitis diagnosed?
- lesion swabs positive
- blood cultures
- Skin biopsy
What are the defining characteristics of pyoderma gangrenosum?
- Ulceration of legs
- History of inflammatory bowel disease
Describe necrotising fasciitis
- 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
Describe anthrax
- B.antharcis
- spore forming aerobic gram +ve bacillus
- wool, hair, animal hides
- Woolsorter’s disease
- imported drum skin, injecting drugs
- Malignant pustule, septicaemia, eschar
What are anaerobic infections of skin & soft tissue?
- Gas gangrene: palpable subcut gas
- C.perfringens
- IV antibiotics & surgical debridement
What antibiotics are best used for:
- Staph aureus
- Penicillin allergy
- Anaerobic infections
- MRSA
- SA: flucloxacillin
- PA: erythromycin
- A: metronidazole
- MRSA: vancomycin
What are common dermatophyte infections?
-Skin= tinea corporis, tinea pedis (athletes foot) tinea cruris
-Nails= onychomycosis
-Scalp= scalp ringworm
Cause: T.rubrum, M.canis
What is the pathogenesis of fungal infections?
- Dermatophytes use keratin as nutrition
- Restricted to stratum corneum
