Fungal and bacterial skin infections Flashcards
1
Q
Classification of soft tissue infections (STI)
A
- superficial
- deep localized
- deep spreading
- muscle involvement
2
Q
Impetigo
A
- Superficial infection, usually of strep pyogenes (group A), sometimes staph aureus
- Intra-epidermal
- Vesiculopustular lesion, later crusts
- Begins as small vesicles, rapidly pustulate and rupture
- Bacteria colonize skin 10 days prior to lesions
- Rx: penicillin or cephalosporin
- Can lead to post-strep glomerulonephritis (GN)
3
Q
Bullous impetigo
A
- Due to specific type of S aureus
- Cause by exfoliative toxins, leads to subcorneal separation of cells
- Usually in newborns and young
- Vesicles become flaccid bullae, rupture and leave thin brown crust
4
Q
Erysipelas
A
- Superficial cellulitis, bright red edematous, indurated (hardened, orange-peel), with sharp raised border
- Due to group A strep, most common in elderly and young
- Often affects lower extremities, face
- Rx: systemic penicillin
5
Q
Folliculitis
A
- Pyoderma located in hair follicles and apocrine regions
- Small erythematous papules topped by central pustule
- Commonly found on hips, butt, axilla
- Usually due to staph aureus, or p aeruginosa (hot tubs), candida
6
Q
Furuncles
A
- Furuncle (boil): deep inflammatory nodule usually due to preceding folliculitis (usually staph aureus)
- Carbuncle: multiple abscesses separated by connective tissue septae, and drain to surface along follicle (staph is usually pathogen)
- Both forms of abscesses usually in IV drug users
- Rx for both: systemic antibios against staph, incise and drain
7
Q
Cellulitis
A
- Acute spreading infection of the skin extending deep to involve subcutaneous tissue
- Frequently caused by group A strep or staph aureus
- Rx: elevation and antibio therapy
8
Q
Necrotizing STI
A
- Uncommon, necrosis of deep soft-tissue (subQ fat and fascia, late involvement of muscle) with progressive spread
- High mortality even w/ therapy
- Anaerobic wound environment, production of lytic nzs, bacterial synergy
- Signs: edema, erythema, skin vesicles/bullae, subcutaneous gas, no lymphangitis or lymphadenitis, lots of pain
- Fourniers: scrotal
9
Q
Necrotizing fasciitis
A
- Involvement of deep layer of superficial fascia, sparing of deep fascia and muscle
- Caused by strep (but not group A), alone or w/ GN bacilli
- Rx: debridement, antibios, supportive care
10
Q
Gas gangrene
A
- Due to contamination of muscle injury, usually C perfringes
- Intense pain, swelling and systemic toxicity
11
Q
Bite wounds
A
- Animal: polymicrobial infections (staph aureus, strep, mouth anaerobes)
- Dogs: pasturella canis, open wounds
- Cats: pasturella multocida, puncture wounds
- Rx: wounds should be cleaned and left open, use antibios
- Human: often involves hand, also polymicrobial (E corrodes, S aureus, strep), same Rx
12
Q
Syphilis
A
- Infectious disease (treponema pallidum)
- Primary stage: ulcerated papule, can Dx by serology or darkfield microscopy
- Secondary stage: widely dispersed, maculopapular on palms and soles
- Latent: serologic proof, but no symptoms (can last years)
- Tertiary: gummatous, neurosyphilis, cardiovascular syphilis
13
Q
Fungal skin infections
A
- Dx by KOH prep (tinea versicolor can also be by Wood’s light)
- Superficial mycoses (stratum corneum, hair follicles only)
- Dermatophytoses (stratum corneum, hair, nails)
- Intertrigo (cutaneous candida syndromes)
- Rx w/ topical/systemic antifungal
14
Q
Superficial mycoses
A
- Stratum corneum only (or follicle)
- Tinea (pityriasis) versicolor: white scaling macules caused by Malassezia furfur (normal commensal). Common in tropics (w/ sun exposure). Non-pruritic, on trunk and proximal limbs, hypo or hyperpigmented (due to azaleic acid).
- Dx by wood’s light (yellow-green, except for trichophyton) or by KOH prep (look for hyphae: spaghetti and meatballs)
- Tinea negra: black macules caused by Hortaea wernechii
- White piedra: white hair nodules caused by trichosoron beigelii
- Black piedra: black hair nodules caused by piedraia hortae
15
Q
Dermatophytoses
A
- Stratum corneum, skin, hair, nails only, most common in feet, groin, scalp, nails
- Unlike superficial mycoses the host immune system may be evoked (results in changes in deeper skin layers)
- Dermatophytes (3 genera): Trichophyton rubrum is most common cause (skin, hair, nails), also microsporum (skin and hair) and epidermophyton (skin and nails)
- Disease are often called ringworm or tinea (zoophilic)
- Tinea pedis (athlete’s foot), tinea unguium (nails), tinea corporis (body), tinea manuum (hands), tinea capitis (scalp), tinea cruris (groin, jock itch)
- Typical lesion: annular scaling patch w/ raised margin and variable degree of inflammation
