Dermatology SC026: It Is Red And Painful (Bacterial And Viral Skin Infections) Flashcards
Common skin infections that can be managed ***surgically in office
Under LA:
1. Infected sebaceous cyst
- Aspiration with syringe if pus collection —> Antibiotic —> see if subside —> Excision of cyst later (smaller scar)
- Incision + Drainage if pus collection +/- Avulse cyst wall (which secrete sebum) —> pack with saline gauze —> Excision of cyst later (~4-6 weeks)
- Skin abscess
- Preauricular abscess
- Imperfect fusion of small tubercles of 1st and 2nd branchial arches
- Need drainage then excision of sinus tract (simply drainage cannot solve problem) - Infected wounds
- Rule out underlying causes
- Remove stitches, debris, foreign body
- Antibiotics
- Dressing
- A drain does NOT prevent infection - Sacral sores
- Avoid prolonged pressure + give pressure cushion
- Remove necrotic tissue + let it heal by secondary intention (~ months)
- Dressing
- Reconstructive surgery by skin flap - Anorectal abscess
- Underlying causes: DM, Fistula-in-ano, Sebaceous cyst, Folliculitis
Local anaesthetic
- Block Na channel —> inhibit nerve conduction
- Lignocaine (Xylocaine), Marcaine etc.
- Works in alkaline environment (pH>7), less effective in acidic environment (e.g. ***infected tissue)
- Can increase dose with adrenaline —> NOT to use in digital block / area with end artery supply
Lignocaine:
- Rapid onset
- 3.5 mg/kg (max dose), 60-90 mins
- 5-6 mg/kg with adrenaline, 2-3 hours
Marcaine:
- Slow onset
- 2.5 mg/kg, 4 hours
- 3.5 mg/kg with adrenaline, 6-8 hours
Toxicity:
- First symptom: Nausea
- CNS: twitching of muscle, tremor, tonic clonic seizure, drowsiness, unconsciousness, respiratory arrest
- Cardiac: hypotension, bradycardia, ventricular arrhythmia
Treatment:
- Avoidance of IV injection
- Stop injection
- CVS monitoring
- O2
- IV lipid
Skin incision
- Along skin creases —> least tension —> less scar formation
- Beware CN7: just underneath SC tissue in deep fascia
Wound healing by secondary intention
Granulation tissue —> Scar
Underlying causes for skin infection
- DM
- Immunosuppression
- Medication (e.g. steroids, cytotoxics)
- Dental abscess (may come out through chin, sometimes patient may not notice pain ∵ denture / previous dental root treatment —> no sensation)
- Sinusitis
- Sebaceous cyst
- Preauricular sinus
- Pilonidal sinus (congenital defect, penetration of skin by hair / hair follicle infection)
- Foreign bodies
- Trauma
Skin infection requiring ***hospitalisation
- Carbuncle
- Furunculosis
- Abscess in SC tissue (shallow)
- Microabscess —> No big abscess cavity —> Cannot simply drain it —> Need to excise / debride
- Staph aureus
- Inflammation spreads from hair follicles to dermis
- An acute inflammation with pustular discharge
- Underlying causes: DM, Immunosuppression
- Antibiotics +/- Debridement - Deep abscess with cutaneous manifestation
- Management of underlying causes
Skin infection requiring urgent admission
- Ludwig’s angina
- Rapidly expanding cellulitis of Floor of mouth, Submandibular, Submental space —> edema causing **airway obstruction (∵ push tongue upwards + backwards)
- Hot potato voice (∵ tongue not moving) —> impending airway obstruction
- Need **airway protection, drainage, antibiotics, monitoring
- Underlying causes: DM, Dental abscess, Poor dentition, Submandibular gland infection - Fournier’s gangrene
- Acute gangrenous bacterial infection of scrotum, penis, perineum involving SC fat + superficial fascia
- Underlying causes: DM, Fistula-in-ano
- Mortality rate 30%
- Need extensive debridement (∵ tissue is dead —> no bleeding at all)
- Broad spectrum antibiotics (simply antibiotic not enough —> ∵ tissue is dead —> antibiotic cannot reach —> need surgery to debride dead tissue) - Necrotising fasciitis
- Rapidly progressing soft tissue infection (< a few hours) with systemic toxicity + high mortality
- Group A Streptococcus, Staph aureus, Mixed flora
- Underlying causes: DM, Immunosuppression
- Classical presentation: **Minor trauma —> Excruciating pain (but wound can be small)
- Clinical features: Inflammation, **crepitus, systemic toxicity, fever, rapid progression over hours, skin blistering / gangrene
- Urgent debridement of dead tissue + Antibiotics
Classification of Cutaneous infection
- Fungal
- Superficial: Dermatophytes, Yeast
- Subcutaneous
- Deep - Bacteria
- Impetigo
- Erysipelas
- Cellulitis
- Furuncles, Carbuncles
- Folliculitis
- Erythrasma
- Necrotising SC infection
- Staphylococcal scalded skin syndrome - Viral
Impetigo
Causes:
- **Staphylococcus (produce toxin that split skin) / **Streptococcus
S/S:
- **Vesicles / Pustules that arise on **erythematous base with ***crusting formation (∵ skin split)
- In skin damaged by previous minor trauma e.g. scratching
Diagnosis:
- Clinical
- Skin swab (just not to miss MRSA)
Treatment:
- ***Oral Cloxacillin + Ampicillin
- Topical antibiotic
Erysipelas / Cellulitis
Causes:
- ***Streptococcus, Staphylococcus, Haemophilus influenzae
- Erysipelas: involve ***dermal lymphatic
- Cellulitis (even deeper): involve ***deep dermis + SC tissue
- Site of entry: minor skin break from scratching / tinea infection
S/S:
- Inflammed + tender skin
- Systemic symptoms common: fever, lymphadenitis
Treatment:
- IV antibiotics (Ampicillin/Cloxacillin or Cephalosporin/Cloxacillin)
Folliculitis / Furuncles / Carbuncles
Folliculitis: Inflammation of hair follicle
Furuncles: Follicular staphylococcal infection with pustules formation
Carbuncles: Multiple furuncles grouped together to form abscess
- Recurrent infection: need to rule out immunosuppression (i.e. DM)
Treatment:
- Folliculitis: Improve hygiene, 3 months course of tetracycline for resistant cases
- Furuncles / Carbuncles: Antibiotic short course +/- Incision and drainage
Itchy:
- not liklely to be bacteria —> more likely to be fungal (e.g. Pityrosporum folliculitis)
Erythrasma
Causes:
- ***Corynebacterium minutissimum
S/S:
- Involve intertriginous area e.g. axilla, groins, toeweb
- Slight **brown erythematous scaly patch
- **Pink fluorescence under Wood’s light
Treatment:
- Oral Erythromycin
- Topical Whitfield
Necrotising SC infection
Infections producing ***necrosis of SC tissue that may include the fascia (hence necrotising fasciitis)
Causes:
- Streptococcus
- Mixture of aerobic and anaerobic bacteria
S/S:
- Common sites: Limbs, Perineum
- Complication of cutaneous infection / perceding surgery
- Severe local pain (disproportionate to size of lesion), marked tender, edematous
- Skin becomes **violaceous (purplish), bullae formation, **crepitus, ***gangrene
- Fever, systemic toxicity
- Rapid progression with mortality 6-67%
Treatment:
- Surgical exploration + IV antibiotic (Gentamicin, Fortum (Ceftazidime))
Features to differentiate NF from Cellulitis:
- Edema beyond apparent limit of infection
- Development of **bullae, **ecchymoses
- Dermal gangrene
- **Numbness in infected area (∵ nerve involved)
- **Crepitus
- Severe pain ***disproportionate to clinical finding
- Poor response to antibiotic
- MRI: allow early diagnosis of NF
Staphylococcal scalded skin syndrome
- ***<5 yo (∵ great SA to BW ratio —> bacteria can produce enough exotoxin to split skin —> widespread exfoliation)
- Immunocompromised adult / elderly (e.g. HIV, lymphoma, CRF)
- ***Exfoliative toxin
- Fever, tender erythematous skin, exfoliation
- Positive ***Nikolsky sign
- Mortality: 4% in newborn
Diagnosis:
- Clinical
- Culture
- ***Tzanck smear
Treatment:
- ***Systemic antibiotic
Cutaneous TB
- Exogenous
- Primary inoculation
- Tuberculoisi verrucosa cutis - Endogenous
- Lupus vulgaris
- Scrofuloderma
- Metastatic TB abscess
- Acute miliary TB
- Orificial TB - TB due to BCG
- Tuberculids
- Lichen scrofulosorum
- Papulonecrotic tuberculid - Facultative tuberculids
- EN
- EI (Erythema induratum) - Others
- Lupus miliaris disseminatus faciei
