Cutaneous Infections Flashcards
1
Q
What is impetigo?
A
- common superficial bacterial infection (most often in childhood)
- highly infectious (direct contact)
- Staph aureus (less commonly strep pyogenes)
2
Q
What are the clinical symptoms of impetigo?
A
- small vesicles that rupture and are replaced by thick yellow crust (honey-colored)
- the mouth, nose, and extremities are most commonly affected
3
Q
What is bullous impetigo?
A
Less common bullous form; caused by the epidermolytic toxin of staph aureus
4
Q
What does impetigo look like on histology?
A
- spongiotic epidermis with neutrophilic infiltrate
- bacterial cocci can be demonstrated using Gram stain in the superficial epidermis
5
Q
What is staphylococcal scalded skin syndrome?
A
- primarily affects infancts and children
- toxin mediated type of exfoliative dermatitis (toxigenic strains of staph aureus; phage group II type 71)
- 2 exotoxins; epidermolytic toxins A (ET-A) and B (ET-B)
- cause intraepidermal splitting through the granular layer by targeting desmoglein 1
6
Q
What are the clinical signs of staphylococcal scalded skin syndrome?
A
- sudden onset of skin tenderness and a macular eruption
- followed by the development of large flaccid bullae
- face, neck, and trunk (including axillae and groin)
- mucous membranes NOT involved
- good prognosis in children (better at clearing the toxin)
- in adults staphylococcal septicemia may ensue
7
Q
What does staphylococcal scalded skin syndrome look like on histology?
A
- subcorneal splitting of the epidermis
- a few acantholytic cells and sparse neutrophils may be present within the blister
- NO bacteria; toxin mediated
8
Q
What is cellulitis?
A
**deep pyogenic infection
- diffuse inflammation of the connective tissue of the skin and/or the deeper soft tissues
- most common on legs
- expanding area or erythema (tender)
- historically beta hemolytic strep and/or coagulase positive staph infection
- an increasing number organisms are now implicated in the etiology of cellulitis
9
Q
What is erysipelas?
A
**distinctive type of cellulitis;
- bacterial skin infection involving the upper dermis (superficial cutaneous lymphatics)
- more superficial than general cellulitis, deeper than impetigo
- sharply outlined edematous, erythematous, tender and painful plaque (elevated borders)
- more common on lower extremities
- most prevalent in elderly
- strep pyogenes is most common
10
Q
What does cellulitis look like on histology?
A
In both cellulitis and erysipelas, there is…
- marked dermal edema
- lymphatic dilatation
- diffuse infiltrate of neutrophils that is accentuated around blood vessels
11
Q
What are verrucae?
A
**warts
- commonly caused by human papilloma virus (DNA virus)
- low risk and high risk HPV (most warts caused by low risk)
- generally self limiting
- regress spontaneously within 6 months to 2-3 years
- e.g. verruca vulgaris, plantar warts, anogenital warts
12
Q
What is the pathology behind verrucae? What does this look like on histology?
A
- verrucous (thickened) epidermal hyperplasia
- large cells with prominent vacuolated cytoplasm and a small pyknotic nucleus are seen in the upper layers of the epidermis (koilocytes).
- prominent granular cell layer within which are enlarged clumps of irregular basophilic keratohyaline granules
13
Q
What is condyloma accuminatum?
A
**genital warts
- caused by HPV 6 and 11 (>90% of cases)
- sexually transmitted disease
- high risk HPV types (16, 18, 31, 33) may increase risk for cancer
- single or multiple papular lesions that are pearly, filiform (thread-like), fungating (fungus-like), cauliflower, or plaque-like
14
Q
What does condyloma accuminatum look like on histology?
A
- acanthosis (diffuse epidermal hyperplasia) with a broad rounded exophytic growth
- surface of the lesion is hyperkeratotic (excess keratin) and parakeratotic (retention of nuclei)
- superficial vacuolated keratinocytes (koilocytes) are characteristic
- coarse keratohyaline granules may be present
15
Q
Describe HSV
A
**Herpes simplex virus
- HSV-1 and HSV-2 commonly are…
- 1= common in childhood (lips; cold sores/gingivostomatitis)
- 2= after puberty (genitalia, STD)
- although there may be some overlap of the types
- lesions are groups of clear vesicles which heal without scarring
16
Q
What are the most common ways to diagnose HSV?
A
- Tzanck smears
- smear from base of a freshly opened vesicle and stain it with Giemsa stain
- PCR (most sensitive)
- biopsy
17
Q
Describe varicella (chickenpox)
A
- highly contagious and spreads via respiratory droplets (incubation time 2 weeks)
- disease of childhood; rare in adults
- rash progresses from macules to vescicles to pustules (all stages are simultaneously present)
- complications= reye syndrome, pneumonia, and self-limited cerebelitis
18
Q
Describe herpes zoster (shingles)
A
- recurrence of VZV years later
- affects 10-20% of the population during their lifetime
- increased incidence in the elderly and immunocompromised patients
- rash has a unilateral dermatomal distribution (thorax and lumbar)
19
Q
What is the common pathology between VZV and herpes simplex?
A
- acantholysis of epidermis (loss of intercellular connections resulting in loss of cohesion between keratinocytes)
- multinucleated keratinocytes with intranuclear inclusions (Cowdry type A inclusions)
- perineurial and intraneurial (within nerve) inflammation
20
Q
What is molluscum contagiosum?
A
- cutaneous infection caused by a large brick-shaped DNA poxvirus
- highly contagious, self inoculation
- children acquire infection from close contact (eyelids, face, axilla)
- STD on penis, vulva, groin
- widespread disease can be seen in immunocompromised patients
21
Q
What does molluscum contagiosum look like on histology?
A
- inverted “crater-like” nodule of acanthotic and hyperplastic epidermis
- eosinophilic cytoplasmic bodies in keratinocytes just above the basal layer (aka Molluscum bodies/Henderson-Patterson bodies)
22
Q
What are scabies?
A
- caused by the mite sarcoptes scabiei
- erupts 4 weeks after infestation
- mite is transmitted via prolonged direct human contact
- extremely pruritic papulovesicular eruption (called the “7 year itch”)
- fingers, penis, umbilicus, waistband, axilla, hands
23
Q
What do scabies look like on histology?
A
- female S. scabiei mite deposits eggs in the burrows in the epidermis
- burrows extend at a shallow angle through the stratum corneum and may reach the deeper epidermis
- eggs, larvae, mites, mite parts, and excreta may be identified in the stratum corneum
24
Q
What is dermatophytosis?
A
**superficial fungus aka “tinea”
- very common cutaneous infection
- 3 genera; microsprum, epidermophyton, and trichophyton
- clinical appearance is variable (many locations)
- scaly, erythematous plaques, often annular
- KOH prep rapid test to find the branching septate hyphae
25
Q
What are the common locations of dermatophytosis?
A
- tinea capitis (scalp)
- tinea corporis (trunk)
- tinea barbae (beard)
- tinea cruris (groin; “jock itch”)
- tinea pedis (feet)/ manuum (hands)
- tinea unguium (onychomycosis; thickened, yellow nails)
26
Q
What does dermatophytosis/tinea look like on histology?
A
- presence of neutrophils
- compact orthokeratosis (Hyperkeratosis without parakeratosis)
- presence of the ‘sandwich sign’ (presence of hyphae ‘sandwiched in’ between normal basket- weave stratum corneum, and a lower layer of stratum corneum with either orthokeratosis or parakeratosis)
**A periodic acid-Schiff (PAS) stain can reveal the fungus.
27
Q
What is tinea versicolor?
A
**aka pityriasis versicolor
- common superficial infection in tropical climates
- young adults (20-40 yo)
- caused by Malassezia globosa/furfur (fungi)
- multiple irregular areas of hypo or hyperpigmentation, which are circular and macular
28
Q
What does tinea versicolor look like on histology?
A
- the stratum corneum contains round budding yeasts and short septated hyphae,
- ‘spaghetti and meatballs’ appearance
- organisms are clearly seen in H&E and PAS preparations
