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
Cutaneous viral infection
2 types:
1. Viral exanthems (exanthem: widespread rash over whole body)
- Chicken pox
- Coxsackie
- Infectious mononucleosis
- Rubella
- Localised viral infections
- Warts
- Herpes
- Molluscum contagiosum
Viral warts
Causes:
- HPV (many types)
- Transmitted by ***contact
Genital wart:
- ***Sexually transmitted
S/S:
- Wart lesions with blood vessels (black dots) beneath surface
—> vs Callus (thickened skin due to uneven pressure on feet): blade to peel off skin —> if black dots appear (i.e. blood vessels) —> Wart
- Painful in sole
- Genital wart can be associated with neoplastic changes (cervical cancer / SCC)
Treatment:
- **Salicylic acid
- **Cryotherapy
- Cauterisation
Molluscum contagiosum
Cause:
- ***Pox virus
- Transmitted by contact, common in children (eczema —> scratch —> physical contact with others)
- can be sexually transmitted
S/S:
- Skin coloured dome shape umbilicated papules with central depression (can be visualised with dermoscope / liquid nitrogen)
- Itchy sometimes
Treatment:
- Salicylic acid
- Cryotherapy
- Cauterisation
Varicella (Chicken pox)
- Highly contagious due to VZV
- Usually children
S/S:
- Erythema **macules —> quickly develop into **vesicles, pustules
- associated with systemic symptoms
- more complications if occur in adults (e.g. pneumonitis, headaches, encephalitis)
- Incubation period: ***14 days
Herpes zoster
- Reactivation of latent VZV (suppressed by Ab produced by B cells)
- usually elderly
S/S:
- Dermatomal distribution
- **Painful erythematous eruption —> followed by **vesicles, pustules formation —> clustered into a ***herpetiform arrangement
- Can be multi-dermatodermal / disseminated if immunocompromised
Complications:
- **Post-herpetic neuralgia (main complication)
- **Herpes zoster ophthalmicus (if involve **CNV1 can affect eye —> intraocular inflammation —> blindness)
- **Ramsay-Hunt syndrome (ipsilateral CN7, CN8 involvement)
Diagnosis:
- Clinical
- Viral culture
- Electron microscopy
- PCR
- Viral Ag detection
- Tzanck smear
Treatment:
1. **Systemic high dose Antiviral (if **<72 hours)
—> Aciclovir (800mg 5 times per day) / Valaciclovir / Famciclovir
2. Supportive measures (e.g. Pain control, Topical antibiotic)
Aciclovir / Valaciclovir / Famciclovir:
- Guanosine analogue
- Selectively phosphorylated by HSV, VZV thymidine kinase
- Inhibit viral DNA polymerase —> Interfere with viral DNA synthesis
- Valaciclovir / Famciclovir: better oral bioavailability (TDS rather than 5 times a day)
Superficial fungal infection
Dermatophytes: an Infection —> **Dermatophytosis (Ringworm)
Yeast (Candida): can be a normal coloniser —> **Candidiasis
Candidiasis:
- Associated with Immunocompromised (DM) / Antibiotic overuse
- Affect mucocutaneous area: oral, vaginal, intertrigo
- House wife dermatitis with loss of nail cuticle can lead to candidiasis paronychia (an infection)
- Treatment: Anti-fungal useful
Types of superficial dermatophytes infection:
1. Tinea unguium / Onychomycosis (nail)
2. Tinea pedis (feet)
3. Tinea cruris (groin)
4. Tinea corporis (trunk)
5. Tinea manuum (hands) (Two feet-one hand syndrome (TFOHS): by Trichophyton rubrum)
6. Tinea capitis (scalp)
- break in skin surface, warm, moist
- ringworm: skin try to overgrow fungi —> central clearing with spreading edge —> culture need scraping of ***edge (NOT centre)
Treatment:
1. Topical antifungal
- against dermatophyte, yeast, both
- works by inhibiting various enzymes needed for **sterol (ergosterol) synthesis in the fungal cell membrane
- should be used **after skin scraping for fungal microscopy + culture —> get accurate diagnosis of fungal infection (need to rule out other DDx e.g. psoriasis, trauma)
- types:
—> Keratolytic (Whitfield)
—> Undecanoate (Acid zinc salt in mycota powder)
—> Thiocarbamates (Tolnaftate)
—> **Morpholines (Amorolfine)
—> **Imidazole (Miconazole)
—> ***Allylamines (Terbinafine)
(Allylamines, Thiocarbamates: inhibit Squalene —> Lanosterol
Azoles, Morpholines: inhibit Lanosterol —> Fecosterol
Morpholines: inhibit Fecosterol —> Episterol)
- Systemic antifungal
- indications:
—> **Scalp (∵ want to prevent scarring)
—> **Nail (∵ topical cannot penetrate enough nail)
—> Extensive tinea infection
—> Immunosuppressed
- types:
—> Grisefulvin (very old, not used now)
—> **Azoles
—> **Allylamines
General SE of Antifungal:
- GI
- Taste
- Liver
- Skin eruption
- Headache
**Hepatotoxicity:
- occur in all antifungal
- develop 4-6 weeks after start of medication
- 1 death in HK as an indirect event
- **monitor liver function before + 4 weeks later among active Hep B
Azole vs Allylamine
Azole:
- Bind to cytochrome p450: **Enzyme inhibitor
- **Itraconazole, ***Fluconazole, Ketaconazole (no longer use ∵ liver toxicity)
Advantage:
- Effective against yeast + dermatophytes
- Stay in tissue after systemic clearance —> Intermittent therapy useful (e.g. 1 week course —> 3 weeks off —> 1 week course)
Disadvantage:
- ***Fungistatic (not very aggressive —> not useful if pure dermatophyte infection)
Allylamine:
- ***Terbinafine
Advantage:
- **Fungicidal
- Effective against dermatophyte
- Minimal SE: GI upset, loss of taste, rarely rash / **liver impairment (LFT baseline + 4 weeks later esp. for prolonged course / Hep B carrier)
- ***Allylamine seems to be better than Azole in cure rate
Blistering disease
Classification:
1. Subcorneal (most superficial)
- Impetigo
- Intraepidermal
- Acute dermatitis (aka Spongiosis, Pompholyx (if in hands))
- Herpes
- Friction
- Erythema multiforme (dermal-epidermal junction)
- ***Pemphigus - Subepidermal (underneath epidermis —> roof of blister much thicker —> intact bulla)
- ***Bullous pemphigoid
- Dermatitis herpetiformis (uncommon, associated with gluten enteropathy)
- Porphyria (abnormality of Hb metabolism —> sunlight exposure —> blister)
***Pemphigus, Bullous pemphigoid —> main DDx of SJS
Pemphigus
- ***4-6th decade
- ***Intraepidermal blister
- AutoAb against **keratinocytes (cell **within epidermis) (Organ-specific autoimmunity) —> Desmoglein 1, 3 in Epidermal intercellular layer —> break cell apart (Acantholysis)
- ***Disease more severe, before systemic steroid: mortality 80%
S/S:
- Flaccid blister (∵ thin roof) in skin + mucosa (intraepidermal) —> **burst —> crusting
- Normal skin in between lesions
- Not itchy
- Affect trunk and face, **mucosal surface, extremities spare
- ***Nikolsky sign +ve
Investigation:
- Skin biopsy + Immunofluorescence
- Serum Ab (IDIMF): against keratinocytes (titre correlate with disease activity)
Bullous pemphigoid
- More common in ***elderly
- AutoAb against ***basement membrane (Dermal-epidermal junction)
S/S:
- Large **intact blister arise from urticarial base
- Thigh, groin, axilla
- Mucosal **less common
- **Less severe than Pemphigus
- Can be very **itchy (prodrome)
Investigation:
- Skin biopsy + Immunofluorescence
- IDMIF: level NOT correlate with disease activity
