10 - Cutaneous Infections Flashcards
What causes impetigo and who does it occur in? How does it spread?
Highly infectious superficial bacterial infection that usually occurs in children. Spread by direct contact.
Staph aureus (less commonly pyogenes)
What is the apeparance of impetigo?
Small vescicles that rupture and are replaced by thick yellow crust (honey-colored).
The mouth, nose, and extremeties most commonly affected.
What is bullous impetigo caused by? What does impetigo look like on histology?
Epidermolytic toxin of staph aureus.
Lots of PMNs and bacteria, often under epidermis.
What is staphylococcal scalded skin syndrome? What causes it?
Toxin-mediated type of exfoliative dermatitis.
Toxigenic strains of s. aureus (phage group II, type 71)
- Two exotoxins: epidermolytic toxin A (ET-A) and epidermolytic toxin B (ET-B).
These cause intraepidermal splitting through the granular layer by targeting desmoglein 1.
What is the pathogenesis of staphylococcal scalded skin syndrome? Where does this occur on the body?
Sudden onset of skin tenderness and macular eruption followed by development of large fragile bullae.
Face, neck, trunk, axillae and groin. Mucous membranes not involved.
Who gets staphylococcal scalded skin syndrome? What is the prognosis?
Primarily infants and children.
In adults, a staphylococcal septicemia may ensure.
Describe staphylococcal scalded skin syndrome on histology?
Split between the cornified layer and the granular layer.
Toxin mediated - so not much bacteria present.
What is cellulitis and where does it commonly occur?
Deep pyogenic infection with diffuse inflammation of connective tissue of the skin and/or deeper soft tissue.
Expanding areas of erythema.
Most common on legs.
What can cause cellulitis?
B-hemolytic streptococci and/or coagulase + staphylococci
What is erysipelas? What does it look like clinically?
Bacterial skin infection involving the upper dermis (superficial cutaneous lymphatic)
Sharply outlined edematous, erythematous, tender, and painful plaque (elevated borders).
Who does erysipelas usually occur in? What most commonly cuases it?
Most prevalent in elderly.
More common on lower extremeties.
Usually caused by S. pyogenes (other strep or S aureus)
What is seen on histology of erysipelas?
Edema in the papillary dermis.
What causes verrucae (warts)? How do you treat them?
Human papilloma virus (DNA virus): vularis, plantar, anogenital
Generally self-limited and regress spontaneously within 6mo-2-3yrs.
Most warts caused by low risk HPV.
What is the pathology of verrucae (warts)?
Epidermal hyperplasia
Koilocytosis (cytoplasmic vacuolization) of the upper layer of the epidermis
Infected cells show keratohyaline granuels and intracytoplasmic aggregates
What causes condyloma accuminatum? What is the appearance?
Sexually transmitted disease caused by HPV 6 and 11 (>90% of all cases)
High risk types (16, 18, 31, 33) may increase risk of cancer.
Single or multiple papular lesions that are pearly, filiform, fungating, cauliflower, or plaque-like.
What is seen on histology in someone with condyloma accuminatum?
Massive epidermal hyperplasia
Dome shaped
Intracytoplasmic inclusions higher up in the dermis
What type of virus is herpes virus? What are the two types?
dsDNA herpesvirus (lipid enveloped)
simplex and varicella-zoster
Describe the two types of herpes simplex virus?
HSV1: common in childhood, lips (cold sore or gingivostomatitis)
HSV2: after puberty, genitalia, sexually transmitted
Lesions: group of clear vesicles which heal without scarring
How is varicella zoster spread and how does it progress? Who gets it?
Respiratory route (2 week incubation); progresses from macules to vesicles to pustules (all stages simultaneously present)
Disease of childhood.
What are complications of varicella zoster?
Reye syndrome, pneumonia, self-limited cerebelitis
What is herpes zoster? Who gets it?
Shingles!
Reactivation of latent VZV years later; affects 10-20% of population.
Increased incidence in elderly and immunocomp.
Rash has unilateral dermatomal distribution.
What is the pathology of herpes virus (simplex and VZV)?
They show the same histologic changes:
- acantholysis of epidermis
- multinucleated keratinocytes with intranuclear inclusions (cowdry type A inclusions)
- perineurial and intraneurial inflammation (around the nerve)
What lab test can test for VZV? How does it work?
Tzanck smear
- made from base of freshly opened vesicle and staining it with Giemsa stain
- look for multinucleated keratinocytes
What causes mulluscum contagiosum? Who gets it?
Cutaneous infection causd by a large brick-shaped DNA poxvirus.
Children acquire infection from close contact (eyelids, face, axilla), immunocompromised.
Highly contagious, self innoculation can occur.
What is the appearance of molluscum contagiosum? Where is it seen?
Seen on penis, vulva, and groin (STD)
Shiney, dome-shaped smooth papules, some of which are crater-like (inverted noculde).
What does molluscum contagiousum look like on histology?
Inverted nodule (crater-like)
Eosinophilic sytoplasmic bodies (molluscum bodies “henderson-patterson bodies”)
What causes scabies? How is it transmitted?
A mite sarcoptes scabiei - transmitted via prolonged direct human contact and rarely fomites.
Where does scabies occur and what does it look like?
Fingers, penis, umbilicus, waistband, axilla, and hands.
Erupts 4 weeks after infestations.
Extremely pruritis papulovesicular eruptions.
What does scabies look like on histology?
Mite burrowing through cornified layer.
What is dermatophytosis? What are the three genera?
AKA tinea; very common supoerficial cutaneous infection
Genera: microsporum, epidermophyton, and trihophyton.
What is the clinical appearance of dermatophytosis?
Variable.
Scaly, erythematous plaques, often annular.
What is the name for dermatophytosis of the:
- scalp
- trunk
- beard
- groin
- feet
Scalp: tinea capitis
Trunk: tinea corporis
Beard: tinea barbae
Groin: tinea cruris
Feet: tinea pedis
What are the most common causes of dermatophytosis of the following locations:
- scalp
- trunk
- beard
- groin
- feet
Scalp: T. tonsurans
Trunk: T. rubrum
Beard: T. verrucosum
Groin: T. rubrum and E. floccosum
Feet: T. rubrum
What lab test would you do to identify dermatophytic infections? What would you expect to see?
KOH potassium hydroxide
Scrape, let sit, and look to see branching septate hyphae
When staining tinea with a PAS stain, what would you see on histology?
Inflammatory cells in the epidermis; bright purple/pink hyphae.
(can’t see tinea straight from the normal H&E stain).
What is tinea versicolor? Who would you see this in?
AKA pityrasis versicolor; superficial infection
Seen in tropical climates, typically young adults (20-40 yo)
What causes tinea versicolor? Describe the lesions?
Malassezia globosa or furfur.
Multiple irregular areas of hypo or hyperpigmentation, which are circular and macular
What would you see on histology of tinea versicolor?
Short pseudohyphae and yeast organisms.
