Skin Infections Flashcards
How does Staphylococcus confer Pathogenic properties?
Staphylococcus aureus expresses virulence factors that confer pathogenic properties
What are some diseases caused by Staphylococcus?
Ecthyma
Impetigo
Cellulitis
Folliculitis
- Furunculosis
- Carbuncles
Staphylococcal scalded skin syndrome (SSSS)
Superinfects other dermatoses (e.g. atopic eczema, HSV, leg ulcers)
How does Streptococcus confer Virulence?
Strepococcus pyogenes (β-haemolytic) attaches to epithelial surfaces via lipoteichoic acid portion of fimbriae
- Has M protein (anti-phagocytic) & hyaluronic acid capsule - Produces erythrogenic exotoxins - Produces streptolysins S and O
What are some conditions caused by Streptococcus?
Ecthyma
Cellulitis
Impetigo
Erysipelas
Scarlet fever
Necrotizing fasciitis
Superinfects other dermatoses (e.g. leg ulcers)
How does Folliculitis present?
Follicular erythema; sometimes pustular.
May be infectious or non-infectious.
What is Eosonophilic/non-infectious Folliculitis associated with?
HIV
What is a possible cause of recurrent folliculitis?
Recurrent cases may arise from nasal carriage of Staphylococcus aureus, particularly strains expressing Panton-Valentine leukocidin (PVL).
What is the treatment for Folliculitis?
Antibiotics (usually flucloxacillin or erythromycin)
Incision and drainage is required for furunculosis
What is the difference between a furuncle and a carbuncle?
A furuncle is a deep follicular abscess
- Involvement with adjacent connected follicles
= Carbuncle.
Carbuncle - more likely to lead to complications such as cellulitis and septicaemia
Why do some patients develop recurrent staphylococcal impetigo or recurrent furunculosis?
Establishment as a part of the resident microbial flora
- Abundant in nasal flora
Immune deficiency
- Hypogammaglobulinaemia
- HyperIgE syndrome – deficiency - Chronic granulomatous disease
- AIDS
- Diabetes Mellitus
What happens in Panton Valentine Leukocidin PVL Staphylococcus Aureus
β-pore-forming exotoxin
Leukocyte destruction and tissue necrosis
Higher morbidity, mortality and transmissibility
Skin
- Recurrent and painful abscesses
- Folliculitis
- Cellulitis
- Often painful, more than 1 site, recurrent, present in contacts
Extracutaneous:
- Necrotising pneumonia
- Necrotising fasciitis
- Purpura fulminansWhat are the five C’s of PVL?
Close Contact – e.g. hugging, contact sports
Contaminated items , e.g. gym equipment, towels or razors.
Crowding –crowded living conditions such as e.g. military accommodation, prisons and boarding schools.
Cleanliness (of environment)
Cuts and grazes – having a cut or graze will allow the bacteria to enter the body
What is the treatment for PVL?
Consult local microbiologist / guidelines
Antibiotics (often tetracycline)
Decolonisation – often:
- Chlorhexidine body wash for 7 days
- Nasal application of mupirocin ointment 5 days)
Treatment of close contacts
What happens in Pseudomonal Folliculitis?
Associated with hot tub use, swimming pools and depilatories, wet suit
Appears 1-3 days after exposure, as a diffuse truncal eruption.
Follicular erythematous papule
Rarely: abscesses, lymphangitis and fever.
Most cases self-limited – no treatment required.
Severe or recurrent cases can be treated with oral ciprofloxacin
What happens in Cellulitis?
Infection of lower dermis and subcutaneous tissue
Tender swelling with ill-defined, blanching erythema or oedema
Most cases: Streptococcus pyogenes & Staphylococcus aureus
Oedema is a predisposing factor
How do you treat Cellulitis?
Systemic Antibiotics
What happens in Impetigo?
Superficial bacterial infection, stuck-on, honey-coloured crusts overlying an erosion.
Caused by
- Streptococci (non-bullous)
or
- Staphylococci (bullous)
Caused by exfoliative toxins A & B, split epidermis by targeting desmoglein I.
Often affects face (perioral, ears, nares).
Treated with topical +/- systemic antibiotics.
Where does Impetiginisation occur?
Occurs in atopic dermatitis
- Gold crust - Staphylococcus aureus
What happens in Ecthyma?
Severe form of streptococcal impetigo
Thick crust overlying a punch out ulceration surrounded by erythema
Usually on lower extremities
What is Staphylococcal Skin Syndrome?
Neonates, infants or immunocompromised adults
Due to exfoliative toxin
Infection occurs at distant site (ie conjunctivitis or abscess
∴ Organism cannot be cultured from denuded skin.
In neonates, kidneys cannot excrete the exfoliative toxin quickly
→ Diffuse tender erythema that
→ Rapid progression to flaccid bullae,
→ Wrinkle and exfoliate, leaving oozing, erythematous base
Clinically resembles Stevens-Johnson syndrome / toxic epidermal necrolysis
What happens in Toxic Shock syndrome?
Febrile illness due to Group A Staphylococcus aureus strain that produces pyrogenic exotoxin TSST-1 Fever >38.9°C Hypotension Diffuse erythema Involvement of ≥ systems: – Gastrointestinal – Muscular – CNS - Renal - Hepatic Mucous membranes (erythema) Hematologic (platelets <100 000/mm3) Desquamation predominantly of palms and soles 1-2 weeks after resolution of erythema
What is Erythrasma?
Infection of Corynebacterium minutissimum
Well demarcated patches in intertriginous areas
- initially pink
- Become brown and scaly
What is Pitted Keratolysis?
Pitted erosions of soles
Caused by Corynebacteria
Treated with topical clindamycin
What happens in Erysipeloid?
Erythema and oedema of the hand after handling contaminated raw fish or meat.
Extends slowly over weeks.
Erysipelothrix rhusiopathiae
What happens in Anthrax?
Painless necrotic ulcer with surrounding oedema and regional lymphadenopathy (with pain in lymph nodes) at the site of contact with hides, bone meal or wool infected with Bacillus anthracis.
What happens in Blistering Distal Dactylitis?
Rare infection caused by Streptococcus pyogenes or Staphylococcus aureus
Typically - young children
1 or more tender superficial bullae on erythematous base on the volar fat pad of a finger
Toes may rarely be affected
What happens in Erysipelas?
Infection of deep dermis and subcutis
Caused by β-haemolytic streptococci or Staphylococcus aureus
Painful
Prodrome of malaise, fever, headache.
Presents as erythematous indurated plaque with a sharply demarcated border and a cliff-drop edge
+/- blistering
Face or limb
+/- red streak of lymphangitis and local lymphadenopathy.
Portal of entry must be sought (e.g. tinea pedis).
Systemic symptoms (fever, malaise).
Treated with intravenous antibiotics.
What happens in Scarlet Fever?
Primarily a disease of children
Caused by upper respiratory tract infection with erythrogenic toxin-producing Streptococcus pyogenes
Preceded by sore throat, headache, malaise, chills, anorexia and fever
Eruption begins 12-48 hours later
- Blanchable tiny pinkish-red spots on chest, neck and axillae
- Spread to whole body within 12 hours
- Sandpaper-like texture
Complications: otitis, mastoiditis, sinusitis, pneumonia, myocarditis, hepatitis, meningitis, rheumatic fever, acute glomerulonephritis
What happens in Necrotising Fasciitis?
Initial dusky induration (usually of a limb), followed by rapid painful necrosis of skin, connective tissue and muscle.
Potentially fatal
Usually synergistic: streptococci, staphylococci, enterobacteriaceae and anaerobes.
Prompt diagnosis essential (requires high index of suspicion), followed by broad-spectrum parenteral antibiotics and surgical debridement.
MRI can aid diagnosis.
Blood and tissue cultures can determine organisms and sensitivities.
Mortality is high.
Can affect the scrotum (Fournier’s gangrene).
What happens in Atypical Mycobacterium Infection?
Important cause of infection in immunosuppressed states.
Mycobacterium marinum causes indolent granulomatous ulcers (fish-tank granuloma) in healthy people
- Sporotrichoid (lymph node) spread
Mycobacterium chelonae & abscessus - puncture wounds, tattoos, skin trauma or surgery
Mycobacterium ulcerans: an important cause of limb ulceration in Africa (Buruli ulcer) or Australia (Searle’s ulcer
What happens in Borreliosis/Lyme disease?
Annular erythema develops at site of the bite of a Borrelia-infected tick
Bite form Ixodes tick infected with Borrelia burgdorferi
Initial cutaneous manifestation: Erythema migrans (only in 75%)
- Erythematous papule at the bite site
- Progression to annular erythema of >20cm
What happens 1-30 days after infection in Lyme disease?
1-30 days after infection, fever, headache
Multiple secondary lesions develop - similar but smaller to initial lesion
Neuroborreliosis
- Facial palsy / other CN palsies
- Aseptic meningitis
- Polyradiculitis
Arthritis – painful and swollen large joints (knee is the most affected join)
Carditis
What happens in Tularaemia?
Caused by Francisella tularensis
Acquired through:
- Handling infected animals (squirrels and rabbits)
- Tick bites
- Deerfly bites
Ulceroglandular form
Primary skin lesion is small papules at inoculation site that rapidly necroses – leading to painful ulceration
+/- local cellulitis
Painful regional lymphadenopathy
Systemic symptoms: fever, chills, headache and malaise
What is the Problem with diagnosing Lyme disease?
Serology not sensitive
Histopathology - non-specific
High index of suspicion required for diagnosis
What happens in Ecthyma Gangrenosum?
Pseudomonas aeruginosa Usually occurs in neutropaenic patients Red macule(s) → oedematous → haemorrhagic bullae. May ulcerate in late stages or form an eschar surrounded by erythema
What are some different diagnoses for Escharotic Lesions?
Pseudomonas aeruginosa Usually occurs in neutropaenic patients Red macule(s) → oedematous → haemorrhagic bullae. May ulcerate in late stages or form an eschar surrounded by erythema
What happens in Syphilis?
Treponema pallidum
Primary infection Chancre -painless ulcer with a firm indurated border
Painless regional lymphadenopathy one week after the primary chancre
Chancre appears within 10-90 days
What happens in Secondary Syphilis?
Begins ~50 days after chancre
Malaise, fever, headache, pruritus, loss of appetite, iritis
‘Great mimicker’ – low threshold for testing
- Rash (88-100%) -Pityriasis rosea-like rash
- Alopecia (‘moth-eaten’)
- Mucous patches
- Lymphadenopathy
- Residual primary chancre
- Condylomata lata
- Hepatosplenomegaly
What is Luis malignant?
Rare manifestation of secondary syphilis
Pleomorphic skin lesions with pustules, nodules and ulcers with necrotising vasculitis
More frequent in HIV manifestation
What happens in Tertiary Syphilis?
Gumma Skin lesions - nodules and plaques
Extend peripherally while central areas heal with scarring and atrophy
Mucosal lesions extend to and destroy the nasal cartilage
Cardiovascular disease
Neurosyphilis (general paresis or tabes dorsalis)
What is the diagnosis of Syphilis based on?
Clinical findings
Serology
Strong index of suspicion required in 2ndary syphilis
What is the treatment for Syphilis?
IM benzylpenicillin or oral tetracycline
What happens in Leprosy?
Mycobacterium leprae
Obligate intracellular bacteria - predominantly affects skin & nerves, but can affect any organ
What are the 2 types of Leprosy?
Lepromatous leprosy
- Multiple lesions: macules, papules, nodules - Sensation and sweating normal (early on) - Tuberculoid leprosy - Solitary or few: elevated borders – atrophic center, sometimes annular - Hairless, anhidrotic, numb
What happens in cutaneous TB?
- Exogenously (primary-inoculation TB and tuberculosis verrucosa cutis)
- Contiguous endogenous spread – (scrofuloderma )or autoinoculation – periorificial tuberculosis
- Haematogenous/lymphatic endogenous spread –dissemination (lupus vulgaris, miliary
tuberculosis, gumma
What are the investigations for TB?
- Interferon-γ release assay (Quantiferon-TB)
- Histology – ZN stain
- Culture / PCR
What are the cutaneous manifestations of TB?
Tuberculous chancre Tuberculosis verrucosa cutis Scrofuloderma Orificial TB Lupus vulgaris Miliary TB Tuberculous gumma
What is Tuberculosis Chancre?
painless, firm, reddish-brown papulonodule that forms an ulcer
What is Tuberculosis verrucosa cutis?
wart-like papule that evolves to form redbrown plaque
What is Scrofulderma?
subcutaneous nodule with necrotic material - becomes fluctuant and drains, with ulceration and sinus tract formation.
What is Orificial TB?
non-healing ulcer of the nasal mucosa that is painful
What is Lupus Vulgaris?
red brown plaque - +/- central scarring, ulceration
What is Miliary TB?
pinhead-sized, bluish-red papules capped by minute vesicles
What is Tuberculosis gumma?
firm subcutaneous nodule - later ulcerates
What happens in Molluscum Contagiosum?
Poxvirus infection Common in children & immunocompromised Differential diagnosis - Verrucae - Condyloma acuminata - Basal cell carcinoma - Pyogenic granuloma Usually resolve spontaneously Treatment options – curettage, imiquimod, cidofovir
What happens in Herpes Simplex Virus?
Primary and recurrent vesicular eruptions
Favour orolabial and genital regions
Transmission can occur even during asymptomatic periods of viral shedding
HSV-1 – direct contact with contaminated saliva / other infected secretions
HSV-2 - sexual contact
Replicates at mucocutaneous site of infection
Travels by retrograde axonal flow to dorsal root ganglia
What are the symptoms of Herpes Simplex Virus?
Symptoms with 3-7 days of exposure
Preceded by tender lymphadenopathy, malaise, anorexia
± Burning, tingling
Painful rouped vesicles on erythematous base → ulceration / pustules / erosions with scalloped border
Crusting and resolution within 2-6 weeks
Orolabial lesions – often asymptomatic
Genital involvement – often excruciatingly painful→ urinary retention
Systemic manifestations– aseptic meningitis in up to 10% of omen
Reactivation – spontaneous, UV, fever, local tissue damage, stress
What is Eczema herpeticum?
emergency
Monomorphic, punched out erosions (excoriated vesicles)
acyclovir+antibiotics
What is Herpatic whitlow?
HSV (1>2) infection of digits – pain, swelling and vesicles (vesicles may appear later)
Misdiagnosed as paronychia or dactylitis
Often in children
What is Herpes gladiatorum?
HSV 1 involvement of cutaneous site reflecting sites of contact with another athlete’s lesions
Contact sports e.g. wrestling
What happens in Neo-natal HSV?
Exposure to HSV during vaginal delivery – risk higher when HSV acquired near time of delivery
HSV 1 or 2
Onset from birth to 2 weeks
Localised usually – scalp or trunk
Vesicles → bullae erosions
Encephalitis → mortality >50% without treatment, 15% with treatment → neurological deficits
Requires IV antivirals
Who is at risk of severe/chronic HSV?
Immunocompromised patients e.g. HIV / transplant recipient
Most common presentation – chronic, enlarging ulceration
Multiple sites or disseminated
Often atypical e.g. verrucous, exophytic or pustular lesions
Involvement of respiratory or GI tracts may occur
How is HSV diagnosed?
PCR - don’t need to wait for result
What is the treatment for HSV?
Don’t delay
Oral valacyclovir or acyclovir 200mg five times daily in immunocompetent localised infection
Intravenous 10mg/kg TDS X 7-19 days
How does Varicella Zoster virus present?
Dermatomal
- Single or Multi dermotomal
What happens in Hand foot and mouth disease?
Coxsackie A16, Echo 71
An acute self-limiting coxsackievirus infection
- Echo 71 (associated with a higher incidence of neurological involvement included fatal cases of encephalitis)
Prodrome of fever, malaise, and sore throat
Red macules, vesicles (typically gray and eliiptical), and ulcers develop on buccal mucosa, tongue, palate and pharynx, and may also develop on hands and feet (acral and volar surfaces).
Spread by direct contact via oral-oral route or oral faecal route.
Which viruses cause morbilliform (measles-like) eruptions?
Measles, Rubella, EBV, CMV, HHV6 & HHV7 cause morbilliform (measles-like) eruptions
Leptospirosis
Rickettsia
What causes petechial/purpuric eruption?
Coagulation abnormalities - TTP, ITP, DIC
Vasculitis
Infections
Viruses - Hepatitis B, CMV, Rubella, Yellow fever, Dengue fever, West nile virus
Bacterial (BREN) - Borrelia, Rickettsia, Neisseria, Endocarditis
Other infections - Plasmodium falciparum, Trichinella
Other - TEN, Ergot poisoning, Raynauds
What is Gionati-Crosti syndrome?
A viral eruption that causes and acute symmetrical erythematous papular eruption on face, extremities and buttocks – usually in children aged 1-3 years Causes: - EBV (most common) - CMV - HHV6 - Coxsackie viruses A16, B4 and B5 - Hepatitis B
What happens in Erythema Infectiosum?
Parvovirus B19
Initially: mild fever and headache
A few days later – ‘slapped cheeks’ for 2-4 days
Then reticulated (lacy) rash of chest and thighs in 2nd stage of disease
What is Roseola infantum?
aka exanthem subitum aka 6th disease
Children 2-5 days of high fever Followed by appearance of small pale pink papules on the trunk and head Lasts hours to 2 days. Caused by HHV6 and HHV7 (less commonly)
What is Off?
Caused by parapoxvirus
Direct exposure to sheep or goats
Dome-shaped, firm bullae that develop an umbilicated crust.
Usually develop on hands and forearms
They generally resolve without therapy in 4-6 weeks
What causes warts?
> 200 subtypes HPV
What are the 3 classes of fungal infection?
Superficial
Deep
Disseminated
What happens in Pityriasis versicolor?
superficial fungal infection
Hypopigmented, hyperpigmented or erythematous macular eruption +/- fine scale
Malassezia spp.
Begins during adolescence (when sebaceous glands become active)
Flares when temperatures and humidity are high – Immunosuppression
Topical azole
What are Dermatophytes?
Fungi that live on keratin
What are examples of Dermatophyte infection?
Trichophyton rubrum causes the most fungal infections
Trichophyton tonsurans causes the most tinea capitis
Kerion – an inflammatory fungal infection that may mimic a bacterial folliculitis or an abscess of the scalp; scalp is tender and patient usually has posterior cervical lymphadenopathy
- Frequently secondarily infected with Staphylococcus aureus
What causes dermatophyte infections of the feet?
Trichophyton rubrum – scaling and hyperkeratosis of plantar surface of food Trichophyton mentagrophytes (interdigitale) –sometimes vesiculobullous reaction on arch or side of foot
How can dermatophyte infections of the foot present?
Maceration between the third and fourth toes in the interdigital form
Erythema, scale-crust and bullae in interdigitale form
Tinea pedis. Diffuse scaling
What are Id Reactions?
Aka Dermatophytid reactions
Inflammatory reactions at sites distant from the associated dermatophyte infection
May include urticaria, hand dermatitis, or erythema nodosum
Likely secondary to a strong host immunologic response against fungal antigens
Secondary immune related eczema
What happens in Majocchi granuloma?
Follicular abscess produced when dermatophyte infection penetrates the follicular wall into surrounding dermis; tender
Trichophyton rubrum or mentagrophytes are usually culprit
What happens in Candidiasis?
Candida albicans
Predisposed by occlusion, moisture, warm temperature, diabetes mellitus
Most sites show erythema oedema, thin purulent discharge
Usually an intertriginous infection (affecting the axillae, submammary folds, crurae and digital clefts) or of oral mucosa.
A common cause of vulvovaginitis
May affect mucosae.
Can become systemic (immunocompromise)
What causes Deep Fungal infections?
Capacity for deep invasion of skin or production of skin lesions secondary to systemic visceral infection. Subcutaneous fungal infections – infections of implantation (inoculation) Sporotrichosis Phaeohypomycosis Chromomycosis Mycetoma (Madura foot) Lobomycosis Rhinosporidiosis
When do systemic fungal infections take place?
Systemic respiratory endemic fungal infections Include blastomycosis, histoplasmosis, coccidiodomycosis, paracoccidoiodomycosis, penicillinosis
Disease in both immunocompetent and immunosuppressed
Blastomycosis
Histoplasmosis
Coccidioidomycosis
What happens in Aspergillosis?
Risk factors: neutropaenia & corticosteroid therapy
Primarily a respiratory pathogen
Cutaneous lesions being as well-circumscribed papule with necrotic base and surrounding erythematous halo,
Propensity to invade blood vessels causing thrombosis and infarction
Lesions destructive – may extend into cartilage, bone and fascial planes
Should be considered in differential of necrotisiing lesions
Fusarium causes similar illness and cutaneous lesions both clinically and histologically – (septate hype with acute angle branching)
What happens in Mucormycosis?
Presentation: fever, headache, facial oedema, proptosis, facial pain, orbital cellulitis ± cranial nerve dysfunction
Apophysomyces, Mucor, Rhizopus, Absidia, Rhizomucor
Associations:
Diabetes mellitus (1/3 of patients - DKA very high risk
Malnutrition
Uraemia
Neutropaenia
Medications: Steroids / antibiotics / desferoxamine
Burns
HIV
Treatment: aggressive debridement & antifungal therapy
Culture positive in only 30% of cases
What happens in Scabies?
Contagious infestation caused by Sarcoptes species
Female mates, burrows into upper epidermis, lays her eggs and dies after one month.
Insidious onset of red to flesh-coloured pruritic papules
Affects interdigital areas of digits, volar wrists, axillary areas, genitalia
A diagnostic burrow consisting of fine white scale is often seen
Crusted or ‘Norwegian’ scabies - hyperkeratosis
- Often asymptomatic; found in immunocompromised individuals
Treatment: permethrin, oral ivermectin
- Two cycles of treatment are required
What happens in Head louse?
Head louse- Pediculus humanus capitis
- Entire live cycle spent in hair - 2ndary infection common - Treatment: malathion, permethrin, or oral ivermectin
What happens in Body louse?
Body louse - Pediculus humanus corporis
- Lives and reproduces in clothing – leaves to feed; rarely found on skin - Pruritic papules & hyperpigmentation - Found in overcrowding, poverty & poor hygiene - Eliminated by thorough cleaning or discarding clothes
What happens in pubic louse?
Phithrus pubis aka crabs; three pairs of legs
- Eggs found on hair shaft, also found in occipital scalp, body hair, eyebrow and eyelash, axillary hair - Treatment: malathion / permethrin, oral ivermectin
What happens in Bedbugs?
Cimex lectularius – reddish-brown, wingless insect resembling size and shape of ladybird
- Itchy weals around a central punctum
Dine alone at night, rapidly and painlessly
Live behind wallpaper, under furniture
Fumigation of home is necessary to get rid of pest
Treatment of patient is symptomatic
