Microbiology of the Skin

Question 1

Colonization vs. infection

Answer 1

presence of bacteria in quantities that are insufficient or sufficient (respectively) to cause disease.

Question 2

Pathology of impetigo

Answer 2

Non-bullous (Staph or Strep pyogenes superficial infection) or bullous (S. aureus that secretes toxins that disrupt Dsg) Contracted by direct contact or fomite exposure. Diagnosis w/ superficial culture of wound base or bulla. Tx: topical antibiotics (localized) or oral antibiotics (generalized)

Question 3

Clinical expression of impetigo

Answer 3

Mostly children, but secondarily in open wounds in any age group. Yellow, honey-colored crust, non-healing wound, possible vesicles and pustules in non-bullous. Bullous with flaccid bullae, malaise, fever, diarrhea, appearing non-toxic and rapidly resolving.

Question 4

Aerobic cocci like S. aureus associated with:

Answer 4

impetigo, SSS, abscess

Question 5

coryneform bacteria like corynebacterium minutissimum and proprionobacterium acnes associated with:

Answer 5

erythrasma and acne vulgaris (respectively)

Question 6

Yeast like acinetobacter associated with:

Answer 6

Tinea versicolor

Question 7

Parasites like demodex mites associated with:

Answer 7

rosacea (possibly)

Question 8

Clinical expression of ecthyma

Answer 8

begins as pustules and vesicles that ulcerate and develop thick, adherent crust. Heals w/ scarring. Dx: wound culture. Tx: oral antibiotics

Question 9

Pathology of ecthyma

Answer 9

Strep pyogenes or S. aureus, usually after a trauma

Question 10

collection of pus with surrounding fibrous reaction

Answer 10

abscess

Question 11

abscess that involves a hair follicle

Answer 11

furuncle

Question 12

a collection of furuncles

Answer 12

carbuncle

Question 13

Pathology of abscesses, furuncles, and carbuncles

Answer 13

S. aureus, anaerobic predominate in groin region. Most common in young adults and adolescents.

Question 14

Clinical presentation of abscesses, furuncles, carbuncles

Answer 14

Occur at any site, predilection for sites of trauma or friction. Tender, red nodules that become fluctuant. No systemic symptoms. Tx: warm compress, drainage, indication for oral antibiotics if perinasal, large and recurrent, surrounding cellulitis, or failure to respond locally.

Question 15

Pathology of erysipelas

Answer 15

Strep pyogenes, common in elderly.

Question 16

Clinical expression of erysipelas

Answer 16

erythematous plaque w/ sharply demarcated borders (hallmark). Common on face and lower extremities. Fever, chills, and malaise. Lymphatic destruction if recurrent. Tx: oral antibiotics.

Question 17

Pathology of erythrasma

Answer 17

corynebacterium minutissimus, common in adults.

Question 18

Clinical expression of erythrasma

Answer 18

well-defined erythematous patches with fine scale. Common in axilla, inguinal folds, gluteal cleft, and other sites of moist occlusion. Generally asymptomatic. Dx: WOOD’S LAMP CORAL RED FLUORESCENCE. Tx: topical antibiotics or antifungals.

Question 19

What appears coral red on Wood’s lamp?

Answer 19

erythrasma

Question 20

Epidemiology of tinea corpis, capitis, pedia, and cruris respectively.

Answer 20

capitis: children; corporis, pedis, and cruris (groin): adults. Tinea unguium (nails) in adults

Question 21

Pathology of tinea

Answer 21

Dermatophytes (trichophyton, epidermophyton, microsporum) infection from human-to-human (anthropophilic), animal-to-human (zoophilic), or soil-to-human (geophilic) transmission. Dx: KOH, branching hyphae

Question 22

Clinical presentation of tinea

Answer 22

Capitis: white, scaling patches associated with hair loss
corporis: erythematous, scaling plaques w/ annular configuration
Cruris: erythematous, macerated patches in folds (spares scrotum)
Pedis: plantar erythema and scale extends to lateral feet (mocassin distribution), plantar vesicles/pustules
Onychomyosis: yellow, subungual hyperkeratosis or superficial white scale.
Tx: topical antifungals (clotrimazole or terbinafine)

Question 23

Pathology of Pityriasis (Tinea) Versicolor

Answer 23

Malassezia furfur (yeast) transmitted by direct contact. Common in young adults

Question 24

Clinical presentation of pityriasis versicolor

Answer 24

macules and patches with fine, white, superficial scale more apparent if scraped. Pink in winter. Hypopigmented in summer. Dx: KOH w/ short hyphae and clusters of spores.”spaghetti and meatballs.” Tx: topical antifungal or oral antifungal as needed. Wash twice monthly with selenium sulfide (Selsun Blue)

Question 25

Cutaneous Candidiasis Pathology

Answer 25

Candidia yeast, common in summer or humidity (skin folds or diaper region)

Question 26

Clinical presentation of cutaneous candidiasis

Answer 26

interertrigo: erythematous patches with satellite papules and pustules, maceration, may have foul odor, may involve scrotum. Diaper dermatitis with red papules and plaques with erosions. Dx: KOH pseudohyphae. Tx: topical antifungals (terbinafine not effective). Zinc oxide to protect from maceration

Question 27

Pathology of Seborrheic Dermatitis

Answer 27

Pityrosporum yeast in infants

Question 28

Clinical expression of Seborrheic Dermatitis

Answer 28

Yellow, greasy scale w/ or w/o erythema in seborrheic sites of scalp, glabella, alar creases, chin, chest, inguinal folds. May have papules or maceration. Tx: topical antifungals, add low potency steroid, anti-seborrheic shampoo.

Question 29

Pathology of Herpes Simplex Virus

Answer 29

HSV 1- oral, HSV 2- genital. Transmitted by direct contact, often during subclinical infection.

Question 30

HSV primary, latent, and secondary infections:

Answer 30

Primary: first exposure in seronegative person
Latent: Primary outbreak followed by virus travelling to sensory root ganglion of affected nerve and lays dormant. Triggers immunosuppression, stress, UV light.
Secondary: outbreak in same location as primary

Question 31

Clinical presentation of HSV:

Answer 31

Prodrome of tingling sensation. Painful, uniform vesicles on red base becomes eroded and crusted. Coalescence of vesicles leads to scalloped borders. Lymphadenopathy with primary infection. Erythema multiforme.

Question 32

Describe erythema multiforme in the context of HSV

Answer 32

recurrent, self-limited eruptions of skin or mucosa. May occur concurrently w/ clinical or subclinical HSV. A reaction to underlying infection and HSV not present in lesions. Presents with targetoid (bullseye) macules.

Question 33

Diagnosis and treatment of HSV

Answer 33

Dx: Tzanck prep, serological tests, culture, or PCR
Tx: oral antivirals (acyclovir) w/i 48 hours of onset, reduces duration of symptoms only. When lesions crust, no longer infectious. Topical antivirals ineffective.

Question 34

Pathology of varicella zoster

Answer 34

VZV travels in retrograde direction from affected dorsal root ganglion. Affects people who had primary varicella, higher incidence in elderly and immunosuppressed.

Question 35

Clinical presentation of varicella zoster virus

Answer 35

prodrome of tingling and pain, dermatomal distribution of painful vesicles (hallmark), lymphadenopathy present. Risk of postherpetic neuralgia (chronic pain). Dx: Tzanck prep. Tx: oral antivirals, VZV vaccine

Question 36

Pathology of Warts

Answer 36

HPV (100+ strains) infect basal keratinocytes. Condyloma acuminata in genital mucosa from HPV 16, 18, 33, 35.

Question 37

Clinical presentation of warts

Answer 37

skin-colored papules w/ rough surface, black dots are thromobosed blood vessels. Flat warts may have minimal scale. Hyperkeratotic warts have thick scale.

Question 38

Pathology of molluscum contagiosum

Answer 38

spread by direct contact, affects children and adults, considered an STI in adults

Question 39

Clinical presentation of molluscum contagiosum

Answer 39

asymptomatic skin-colored papule w/ umbilicated center. Rarely pruritic. Tx: resolves spontaneously, cryotherapy, curettage, immunotherapy.

Question 40

Pathology of Erythema Infectiosum

Answer 40

Parvovirus B19, spread through respiratory secretions, common in schoolchildren

Question 41

Clinical expression of erythema infectiosum

Answer 41

Children: rare prodrome of low-grade fever and malaise before rash, red patches on cheeks (“slapped cheek”), lacy, reticulate patches occur after several days.
Adults: prodrome of headache, fever, abdominal pain, may develop arthralgias, risk of aplastic crisis (hemolytic anemia and bone marrow suppresion). ISOLATE FROM PREGNANT WOMEN: risk of hydrops fetalis.

Question 42

Pathology of scabies, dx and tx

Answer 42

Sarcoptes scabies mites in the stratum corneum, causing hypersensitivity reaction up to 2-6 weeks after infection. Dx: scabies prep for mites, eggs, and feces
Tx: Topical antiscabetics (Permethrin 5% cream applied from neck down, including web spaces and skin folds. Rinse in morning, repeat in 1 week), oral antiscabetics (ivermectin), enviromental controls

Question 43

Clinical presentation of scabies

Answer 43

intense itching (especially at night), inflammatory papules, vesicles, and burrow tracks. Affect web spaces, wrists, waistline, sides of hands/feet, penis, scrotum, and nipples. Crusted will have it on hands and feet.

Question 44

Describe a KOH test, its indications and findings

Answer 44

scrape scaling edge of plaque or underside of vesicle, place scale on slide, apply 1-2 drops KOH and cover. Gently heat fix, wait several minutes, and observe under microscope for hypae and/or spores.

Question 45

Describe the Tzanck prep, its indications and findings

Answer 45

Scrape the base of vesicle with a scalpel, place fluid on slide and allow to air dry. Apply Tzancl stain and gently rinse. Observe under microscope for multinucleated giant cells.

Question 46

Describe the scabies prep

Answer 46

scrape edge of burrow with a scalpel down to bleeding point. Place cells on a glass slide. Apply 1-2 drops of mineral oil. Observe under a microscope for mites, eggs, or scybala.