(derm) infections & infestations of the skin Flashcards
why does staphylococcus aureus have pathogenic properties?
has virulence factors on its surface that confer its pathogenic properties
what can staphylococcus aureus cause?
folliculitis (furunculosis, carbuncles)
impetigo
cellulitis
ecthyma
SSSS (staphylococcal scalded skin syndrome)
(can also superinfect other dermatoses, causing leg ulcers etc)
why is streptococcus virulent?
- binds to epithelial surfaces via the lipotechoic acid portion of their fimbrae
- M protein & hyaluronic acid capsule confer anti-phagocytic properties
- produce erythrogenic exotoxins (streptolysins S + O) to damage host cells
what can streptococcus cause?
impetigo
cellulitis
ecthyma
scarlet fever
erysipelas
necrotising fasciitis
(can also superinfect other dermatoses, causing leg ulcers etc)
how does bacterial folliculitis manifest?
follicular erythema, can be pustular
what are the two types of folliculitis?
infectious & non-infectious
give an example of non-infectious folliculitis and name the disease it is associated to
eosinophilic folliculitis
= seen in HIV
what causes recurent cases of S.aureus?
nasal carriage of S.aureus, particular strains expressing Panton-Valentine leukocidin (PVL)
how is folliculitis treated?
antibiotics (after C&S, erythromycin or flucloxacillin)
incision + drainage (for furunculosis)
what is a furuncle?
a singular deep follicular abscess of pus and necrotic tissue
(of the hair follicle)
what is a carbuncle?
form when furuncles develop in adjacent, connected hair follicles
differentiate between furuncles and carbuncles
furuncles = singular follicular abscess of pus and necrotic tissue
carbuncles = adjacent connected furuncles
which of the two are more likely to lead to complications such as cellulitis and septicaemia: furuncles or carbuncles?
carbuncles
what is furunculosis and how is it treated?
development of furuncles in hair follicles
= follicular abscesses filled with pus and necrotic tissue
which bacterial infection can cause furunculosis?
Staphylococcus aureus
why do some patients develop recurrent staphylococcal impetigo or recurrent furunculosis?
1) S.aureus establishes itself as part of the resident microbial flora (e.g. abundant in nasal flora)
2) immune deficiency
- hypogammaglobulinaemia
- hyper IgE syndrome
- chronic granulomatous disease
- AIDS
- diabetes mellitus
what are possible causes of immune deficiency?
- hypogammaglobulinaemia
- hyper IgE syndrome
- chronic granulomatous disease
- AIDS
- diabetes mellitus
what is Panton Valentine Leukocidin S.aureus?
β-pore-forming exotoxin
= a strain of S.aureus with the PVL virulence factoe
what does PVL S.aureus cause in the host?
leukocyte destruction and tissue necrosis
why is PVL S.aureus more dangerous?
higher morbidity, mortality and transmissibility
what are the cutaneous manifestations of PVL S.aureus?
- folliculitis
- cellulitis
- recurrent and painful abscesses
what are the extracutaneous manifestations of PVL S.aureus?
necrotising fasciitis
necrotising pneumonia
purpura fulminans
what are the risk factors of PVL S.aureus?
close contact contaminated items (un)cleanliness crowding cuts & grazes
(5 Cs)
how is PVL S.aureus treated?
1) consult local microbiologist/guidelines
2) antibiotic (usually tetracycline)
3) decolonisation
- chlorhexidine body wash for 7 days
- nasal mupirocin ointment for 5 days
4) treatment of close contacts
which antibiotic is used to treat PVL S.aureus?
usually tetracycline
how is PVL S.aureus often decolonised?
1) chlorhexidine body wash for 7 days
2) nasal mupirocin ointment for 5 days
what is pseudomonal folliculitis?
diffuse truncal eruption of follicular erythematous papules
how does psudomonal folliculitis manifest?
follicular erythematous papules in a diffuse truncal eruption approx 1-3 days after exposure
(rarely also as abscess, lymphangitis, fever)
what causes pseudomonal folliculitis?
hot tub/swimming pool use, wet suit sharing, depilatories
how is pseudomomal folliculitis treated?
usually self-limiting so does not require treatment
BUT
severe, recurrent cases = oral ciprofloxacin
what is cellulitis?
infection of the lower dermin and subcutaneous tissue resulting in blanching erythema and oedema
what does cellulitis often present with?
blanching erythema and oedema
what is the causative agent in cellulitis?
usually S.aureus and S.pyogenes
how is cellulitis treated?
systemic antibiotics
what is impetigo?
superficial bacterial infection
w honey-coloured crusts stuck onto the region overlying an erosion
how does impetigo manifest?
honey-coloured crusts stuck onto the region overlying an erosion
what are the two main causes of impetigo?
streptococcus
staphylococcus
what are the two types of impetigo and what are they caused by?
non-bullous impetigo caused by streptococci
bullous impetigo caused by staphylococci
why do staphylococci cause bullous impetigo?
staphylococci produce exofoliative toxins A & B
= target desmoglein I and split the epidermis
= bullous impetigo (blister formation)
which body regions are affected most commonly by impetigo?
face
perioral, nostrils, ears
how is impetigo treated?
topical or systemic antibiotics
what is impetiginisation?
impetigo in the context of atopic dermatitis
- also caused by S.aureus (but does not blister as usual)
what is the causative factor for impetiginisation?
S. aureus
would expect bullous impetigo but does not blister in this case
what is ecthyma?
severe form of streptococcal non-bullous impetigo
= thick crust overlying ulceration surrounded by erythema
how does ecythma present?
thick crust overlying an ulceration surrounded by erythema
what is ecthyma surrounded by usually?
erythema
where does ecthyma usually present?
lower extremities
what is staphylococcal scalded skin syndrome?
a staphylococcus infection that causes red blistering skin that looks like a burn or scald
which group of people are most commonly affected by SSSS?
neonates, infants and immunocompromised people
what causes SSSS?
where else is this causative agent seen?
the same exfoliative toxin produced by staphylococcus that causes bullous impetigo
why can the causative organism not be cultured from the denuded skin in SSSS?
in SSSS, the infection occurs at a different, distant site to the cutaneous manifestation
= organism cannot be collected and cultured from the site of rash and redness
why does SSSS affect neonates most commonly?
neonates are unable to efficiently excrete the staphylococcal exfoliative toxin via their kidneys
= builds up
= causes SSSS
how does SSSS manifest?
tender erythema
= progresses to flaccid bullae
= wrinkle & exfoliate + erythematous base
which dermatological condition does SSSS clinically resemble?
SJS-TEN
what causes erythrasma?
bacterial infection of Corynebacterium minutissimum
how does erythrasma manifest?
well-demarcated patches in intertriginous areas that are initially pink but become pigmented, brown and scaly
which body regions are most affected by erythrasma?
intertriginous areas e.g. armpit
differentiate between the following: erythrasma, ecthyma and erythema
erythrasma = well-demarcated, brown plaques that form in intertrigionous areas due to Corynebacteria
ecthyma = severe form of streptococcus impetigo with thick crust overlying ulceration
erythema = extensive red rash
what is pitted keratolysis?
bacterial infection of the soled of the feet that presents with pitted erosions
how does pitted keratolysis appear?
pitted erosions of the soles of the feet
= macerated/wet appearance
what is pitted keratolysis often misdiagnosed as?
athlete’s foot
what causes pitted keratolysis?
caused by Corynebacteria
like erythrasma
how are pitted keratolysis AND erythrasma treated?
topical clindamycin
why are both pitted keratolysis and erythrasma treated with topical clindamycin?
both have the same causative agent: Corynebacteria (minutissimum)
what is toxic shock syndrome?
febrile illness cause by S.aureus
what is the causative agent for toxic shock syndrome?
S.aureus that produces the pyrogenic TSST-1 exotoxin
what are the symptoms of toxic shock syndrome?
fever
hypotension
diffuse erythema (can affect mucous membranes)
thrombocytopenia
desquamation of palms and soles
affects other body systems
which body systems are affected in toxic shock syndrome?
gastrointestinal system renal hepatic CNS muscular
which haematological finding is most commonly observed in toxic shock syndrome?
thrombocytopenia
once the erythema of TSS resolves, what happens to the palms and soles?
desquamation usually following 1-2 weeks after resolution of erythema
what is erysipeloid?
erythema and oedema of the hands that extends slowly over weeks
what causes erysipeloid?
caused by handling raw fish and raw meat
erysipelothrix rhusiopathiae
what are the two main manifestations of anthrax?
painless, necrotic ulcer with surrounding ulcer
painful lymphadenopathy
what can cause anthrax?
at the site of contact w hides, bone meal or wool infected with Bacillus anthracis
what are the causative agents for blistering distal dactylitis?
rare infection caused by Streptococcus pyogenes or Staphylococcus aureus
how does blistering distal dactylitis present?
presents w 1 or more superficial bullae/blisters on the fat pads of the fingers
rarely affects toes
who is most affected by blistering distal dactylitis?
young children
what is erysipelas?
infection of the deep dermis that manifests as an erythematous, well-defined plaque and systemic symptoms
what causes erysipelas?
streptococcus, S.aureus
how does erysipelas present?
well-defined, inundated erythematous plaque with a cliff-edge border
systemic symptoms (fever, malaise = prodrome)
lymphangitis, lymphadenopathy
which condition does erysipelas resemble?
cellulitis
= also presents w erythematous plaque but is not as well defined as in erysipelas
how is erysipelas treated?
intravenous antibiotics
what is characteristic of the erysipelas plaque?
cliff-edge border
in which group does scarlet fever present most commonly?
young children
what are the symptoms of scarlet fever?
fever, malaise, chills, headache
12-48 hours after = cutaneous manifestations
what is the causative agent of scarlet fever?
streptococcus pyogenes
what are the cutaneous manifestations of scarlet fever?
pink spots over the face, axilla, and eventually over the body
= have a sandpaper-like texture
what are the possible complications of scarlet fever?
otitis, mastoiditis, sinusitis, pneumonia, myocarditis, hepatitis, meningitis, rheumatic fever, acute glomerulonephritis
how does necrotising fasciitis present?
initial dusky induration
then necrosis of the skin, connective tissue and muscle
how is necrotising fasciitis managed?
high degree of suspicion
immediate administration of broas-spectrum, parenteral antibiotics
surgical debridement
what causes necrotising fasciitis and how can this be determined?
streptococci, staphylococci, enterobacteriaceae and anaerobes
= blood C&S
(MRI can aid diagnosis)
what is Fournier’s gangrene?
when necrotising fasciitis affects the scrotum
in which individuals is mycobacterial infection an important cause of infection?
immunocompromised people
what does Mycobacterium marinum cause?
fish-tank granulomatous ulcers
sporotrichoid spread
what are Mycobacterium chelonae & abscessus associated with?
puncture wounds, tattoos, skin trauma & surgery
what is Mycobacterium ulcerans associated with?
limb ulceration (in Africa and Australia)
when is borreliosis caused?
when an individual is bitten by a Borrelia-infected tick
how does borreliosis manifest?
initially, an erythematous papule that develops into annular erythema (>20cm)
what happens in a borreliosis infection (1-3 days after)?
fever, headache develops
smaller lesions can also develop
what are the possible complications of borreliosis?
neuroborreliosis (CN palsy, polyradiculitis)
arthritis
carditis
how is borreliosis diagnosed?
needs a high index of suspicion
as serology and histopathology non-sensitice
what is borreliosis alternatively known as?
Lyme disease
what causes tularemia?
handling infected animals (squirrels and rabbits)
tick/deerfly bites
what is the most common form of tularemia?
ulceroglandular form
how does tularemia manifest?
small papules, rapidly necrose, form ulcers
what are the symptoms of tularemia?
systemic symptoms (fever, headache, malaise)
cellulitis
regional, painful lymphadenopathy
what is the causative agent for ecythma gangrenosum?
pseudomonas aeurginosa
in which patients is ecthyma gangrenosum most common?
neutropaenic
how does ecthyma gangrenosum manifest?
red papules that become ulcerous and oedematous
eschar w surrounding erythema
how does ecthyma gangrenosum compare to ecthyma?
ecthyma = streptococcus,
ecthyma gangrenosum = pseudomonas
both present w red papules w thick ulcers surrounded by erythema
give three possible causes of escharotic lesions
staphylococcus, streptococcus
Lyme disease
ecythma
how does primary syphilis present?
chancre
(appears within 10-90 days)
with painless, regional lymphadenomathy
what is a chancre in syphilis?
painless ulcer with inundated border
what is secondary syphilis?
if chancre is left untreated, secondary syphilis developed 50 days after
systemic symptoms = fever, headache, pruritus
general cutaneous manifestations = rash, alopecia, residual primary chancre, lymphadenopathy, condylomata lata
why is secondary syphilis likened to sarcoidosis?
both ‘great mimickers’
= low threshold for testing
what kind of rash is seen in secondary syphilis?
pityriasis rosea-like rash
which classic HIV sign can also be seen in secondary syphilis, albeit rarely?
lues maligna
skin lesions w pustules
what are the cutaneous manifestations of secondary syphilis?
pityriasis-rosea like rash
condylomata lata
oral lesions
lues maligna
what can tertiary syphilis lead to?
cardiovascular disease
neurosyphilis
how does tertiary syphilis present?
gumma skin lesions
mucosal lesions destroy underlying cartilage
central areas heal with scarring and atrophy
how is syphilis diagnosed?
clinical findings
serology
(strong index of suspicion required in secondary syphilis)
how is syphilis treated?
oral tetracycline
IM benzylpenicillin
what is the causative agent of leprosy?
mycobacterium leprae
obligate intracellular bacteria - predominantly affects skin & nerves but can affect any organ
what is the clinical spectrum of leprosy?
two main types
1) lepromatous leprosy
2) tuberculoid leprosy
what characterises lepromatous leprosy?
multiple lesions (macules, papules, nodules)
sweating & sensation intact in these lesions
what characterises tuberculoid leprosy?
single/a few lesions (elevated border, atrophic centre, sometimes annular)
hairless, anhidrotic, numb
what is the characteristic difference between lepromatous leprosy and tuberculoid leprosy?
the few lesions in tuberculoid leprosy are hairless + anhidrotic whereas the many lesions in lepromatous leprosy have sensation + sweating intact
does tuberculosis affect the skin?
san affect any organ system, including the skin
only 5-10% of infections lead to clinical disease
what are the types of cutaneous TB?
exogenously
- primary inoculation TB
- tuberculosis verrucosa cutis
contiguous endogenous spread
- scrofuloderma
- autoinoculation, periorificial tuberculosis
haematogenous/lymphatic endogenous spread
- dissemination
- lupus vulgaris, miliary tuberculosis, gummas
which investigations are done for TB in dermatology?
interferon-γ release assay (quantiferon-TB)
histology – ZN stain
culture/PCR
list some cutaneous manifestations of tuberculosis
exogenous:
- tuberculous chancre (papulonodule ulcer)
- tuberculosis verrucosa cutis (wart)
endogenous:
- scrofuloderma (necrotic nodule)
- orificial TB (nasal muscosa ulcer)
haem spread:
- lupus vulgaris (red, brown plaque)
- miliary TB (bluish-red papules)
- tuberculous gumma (firm subcutaneous nodules)
what is molluscum contagiosum and how is it treated?
caused by poxvirus
usually resolves itself but can require cutterage or imoquimod + cidofovir antivirals
in which individuals is molluscum contagiosum most common?
the immunocompromised
children
what are the differentials for molluscum contagiosum?
verrucae
condyloma acuminata
basal cell carcinoma
pyogenic granuloma
which regions of the body are affected most commonly by herpes simplex virus?
orolabial, genital regions
what are the two types of HSV and how are they transmitted?
HSV1 = direct contact w contaminated saliva or other infectious secretions
HSV2 = sexual contact most commonly
(can be transmitted when asymptomatic)
which parts of the body does HSV affect?
replicates at mucocutaneous sites of infection
travels to dorsal root ganglion (via retrograde axonal flow)
what are the symptoms of HSV and when do they occur?
(symptoms occur wihtin 3-7 days of exposure)
primary = tender lymphadenopathy, malaise, anorexia, burning, tingling
cutaneous = vesicles on erythematous base, pustules, erosions, ulceration
systemic = aseptic meningitis
how long does HSV take to completely resolve itself?
approx 2-6 weeks
HSV has orolabial and genital manifestations: which of these are more painful?
orolabial = asymptomatic
genital = excruciatingly painful (urinary retention)
what can cause reactivation of HSV infection?
spontaneous, UV, fever, local tissue damage, stress
which HSV infection can occur in patients with atopic eczema and why is this a problem?
if people with atopic eczema get HSV infection = eczema herpeticum (!)
= medical emergency as it can lead to HSV encephalitis
how is eczema herpeticum treated?
acyclovir IV + antibiotics
how does eczema herpeticum present?
excoriated vesicles
what is herpetic whitlow and who is affected most by it?
either HSV 1/2 infection of digits
= pain, swelling and vesicles; often affects children
(misdiagnosed as paronychia or dactylitis)
what is herpes gladiatorium and who is affected most by it?
HSV 1 involvement of cutaneous site reflecting sites of contact with another athlete’s lesions
= common in contact sports e.g. wrestling
how does neonatal HSV occur?
exposure to HSV 1/2 during vaginal delivery
onset from brith to 2 weeks
how doe neonatal HSV present?
localised = usually scalp or trunk
vesicles = bullae erosions
(complication = encephalitis! can lead to neuro defects if not treated ASAP)
what can neonatal HSV lead to?
HSV encephalitis
how is neonatal HSV treated?
IV antivirals
how does severe/chronic HSV infection present most commonly?
1) chronic, enlarging ulceration
2) at multiple sites or disseminated
3) often atypical e.g. verrucous, exophytic or pustular lesions
(involvement of respiratory or GI tracts may occur)
who does severe/chronic HSV infections affect most?
chronic, immunocompromised patients
how is HSV infection diagnosed?
PCR swab
how is HSV treated?
oral/IV valacyclovir or acyclovir
= don’t delay!
which regions does varicella zoster virus affect?
dermatomal
either affect single dermatome or multiple dermatomes
what causes hand, foot and mouth disease?
coxsackie a16, echo 71
echo 71 = increased risk of encephalitis
how does hand, foot and mouth disease manifest?
grey, elliptical ulcers form in the buccal, oral or hand and foot regions
fever, malaise, sore throat
how is hand, foot and mouth disease spread?
via direct contact
oral-oral or oral-genital
which viruses cause mobiliform (measles-like) eruptions?
measles
rubella
EBV, CMV, HHV6/7
DRUGS!
rikettsia
leptospirosis
what causes petechial/purpuric eruptions?
vasculitis
coagulation abnormalities (DIC)
vial infection (rubellaa, CMV)
bacterial infections (rikketsia, endocarditis)
plasmodium falciparum
what is Gianotti-Crosti syndrome?
acute, symmetrical erythematous papular eruption of the face, extremities and buttocks
who does Gianotti-Crosti syndrome occur most commonly in?
children aged 1-3
what are the main causes of Gianotti-Crosti syndrome?
CMV
EBV
HHV6
hepatitis B
what is erythema infectiosum and how does it present?
‘fifth disease’
- initial fever and headache
- ‘slapped cheek’ rash after 2-4 days
- lacy rash of check and thigh in 2nd stage
(caused by parvovirus B19)
what is roseola infantum and how does it present?
‘sixth disease’
- fever
- pink papules on trunk and head
- lasts 2 hours or days
(caused by HHV6/7)
what is orf and how does it present?
caused by parapoxvirus
dome-shaped bullae with crust develop on the hands or forearms
how is orf spread?
direct exposure to sheep and goats
how is orf treated?
generally resolve without therapy in 4-6 weeks
what causes warts?
> 200 subtypes of HPV virus
