SM_263a: Bacterial and Fungal Skin Infections

Question 1

Superficial cutaneous fungal infections are limited to the ____ and are caused by ____, ____, and ____

Answer 1

Superficial cutaneous fungal infections are limited to the epidermis and are caused by dermatophytes, Malassezia spp., and Candida spp.

(dermatophytes include Trichophyton spp., Microsporum spp., and Epidermophyton spp. and infect keratinzed tissues - stratum corneum, nail, hair)

Question 2

Arthrospores inside hair shafts (endothrix) on KOH stain are indicative of ____

Answer 2

Arthrospores inside hair shafts (endothrix) on KOH stain are indicative of tinea capitis

Question 3

Tinea capitis is spread through ____

Answer 3

Tinea capitis is spread through direct contact with animals, humans, and fomites

Question 4

Describe tinea capitis variants

Answer 4

Tinea capitis variants

• Non-inflammatory: seborrheic, black dot
• Inflammatory: kerion (painful inflammatory boggy mass w/ broken hair follicles, risk of scarring)

Question 5

Tinea capitis is treated ____

Answer 5

Tinea capitis is treated systemically (griseofulvin, terbenafine)

(topical agents are ineffective)

Question 6

Branched septate hyphae on KOH stain are indicative of ____

Answer 6

Branched septate hyphae on KOH stain are indicative of tinea corporis

(parallel throughout entire length)

Question 7

Tinea pedis is known as ____

Answer 7

Tinea pedis is known as athlete’s foot

• May have fine scales on sole and between toes, vesicles often appear on bottom / sides of foot
• Interdigital type: most common, presents with scaling and redness between toes and may have associated maceration
• Mocassin type: sharply marginated scale, distributed along lateral borders of feet, heels, and soles
• Vesicobullous type

Question 8

____ is a potential complication of tinea pedis and involves ____

Answer 8

Onychomycosis is a potential complication of tinea pedis and involves chronic fungal infection of nailbed

Question 9

Onychomycosis should be ____ then ____ and responds poorly to ____

Answer 9

Onychomycosis should be proved then treated and responds poorly to topical antifungals

(identification of fungus in affected nail via positive KOH prep or nail biopsy is necessary before treatment)

Question 10

This is ____

Answer 10

This is tinea corporis

(annular lesion w/ central clearing, caused by T. rubrum / M. canis / T. mentagrophytes)

Question 11

Tinea corporis is also known as ____ and refers to ____

Answer 11

Tinea corporis is also known as ringworm and refers to dermatophytosis of the skin of the body

(itchy, the margin of lesion is most active / central area tends to heal, scraping should be taken from red scaly margin for KOH exam)

Question 12

This is ____

Answer 12

This is tinea versicolor

Question 13

Tinea versicolor is ____ pattern on KOH prep

Answer 13

Tinea versicolor is spaghetti and meatball pattern in KOH prep

Question 14

Describe tinea versicolor

Answer 14

Tinea versicolor

• Not a dermatophytosis
• Caused by overgrowth of Malassezia: lipophilic yeast that is a normal resident in keratin of the skin and hair follicles
• Tends to recur annually in the summer months
• Characterized by variable colored, often rounded, patches - most common trunk
• Visible scale often not present but seen when rubbed with finger or scalpel blade

Question 15

Visible scale not present but scale readily seen when rubbed with finger / blade refers to ____

Answer 15

Visible scale not present but scale readily seen when rubbed with finger / blade refers to tinea versicolor

Question 16

Describe tinea versicolor treatment

Answer 16

Tinea versicolor

• 2.5% selenium sulfide shampoo
• Topical antifungals daily for 2 weeks
• Oral antifungals for recalcitrant disease
• Relapse / recurrence is the rule

Question 17

This is ____

Answer 17

This is diaper candidiasis

(beefy red plaques with very fine white scale in groin area, skin creases involves, satellite papules and pustules noted on inner thigh and abdomen)

Question 18

Diaper candidiasis is characterized by ____ and does not improve with ____

Answer 18

Diaper candidiasis is characterized by satellitle papules and pustules and does not improve with application of barrier creams

(irritant diaper dermatitis is erythema, erosion, spares skin folds, severe cases may show ulcerated papules and islands of re-epithelialization)

Question 19

Describe pathogenesis of diaper candidiiasis

Answer 19

Diaper candidiasis pathogenesis

1. Urease enzymes present in feces release ammonia from urine
2. Acute irritant effect
3. Disruption of epidermal barrier
4. Entry of Candida (present in feces)

(wet and dirty diapers that are not changed on a regular basis contribute to development of diaper dermatitis)

Question 20

Cutaneous candidiasis is most often caused by ____ and treated with ____

Answer 20

Cutaneous candidiasis is most often caused by Candida albicans and treated with topical antifungals

(Candida albicans is part of normal flora of mucous membranes of upper respiratory, GI, and female genital tracts)

Question 21

Candidal intertrigo affects ____, commonly affects ____ patients, manifests as ____ on KOH exam, and is treated with ____

Answer 21

Candidal intertrigo affects large skin folds, commonly affects obese patients, manifests as pseudohyphae, and is treated with antifungal agents

(prevention is keep intertriginous areas dry / cool / clean and encouraging weight loss for obese patients)

Question 22

Sporotrichosis is ____ infection caused by ____ growing on ____ and manifests as a ____

Answer 22

Sporotrichosis is a subcutaenous infection caused by Sporothrix Schenickii growing on decaying vegetable matter and manifests as a dermal nodule then chain of secondary nodules on the course of lymphatics

Question 23

Broad based budding yeast is ___ and can manifest on skin as a result of ____

Answer 23

Broad based budding yeast is blastomycosis and can manifest on skin as a result of dissemination from lungs

(Great Lakes region in the US, thick-walled rounded refractile spheres)

Question 24

Superficial pyodermas are ____

Answer 24

Superficial pyodermas are infections in the epidermis just below the stratum corneum (impetigo) or in hair follicles (folliculitis)

• Staphylococcus aureus is most common cause in industrialized nations
• Group B strep is common cause in babies

Question 25

Bullous impetigo is a bacterial infection caused by ____ and results from a \_\_\_\_

Answer 25

Bullous impetigo is a bacterial infection caused by Gram positive bacteria (Staphylococcus aureus) and results from a secreted exotoxin (disrupts desmogleins in desmosomes -\> causes blisters)

Question 26

Staphylococcal scalded skin syndrome is \_\_\_\_

Answer 26

Staphylococcal scalded skin syndrome is when a focus of infection secretes toxin that bind to desmoglein-1 in the granular cell layer into the blood, leading to widespread blisters (not a skin infection)

Question 27

Staphylococcal scalded skin syndrome is caused by ____ that bind to ____ in the ____ cell layer and produce \_\_\_\_

Answer 27

Staphylococcal scalded skin syndrome is caused by 2 endotoxins that bind to desmoglein-1 in the granular cell layer and produce blistering

Question 28

\_\_\_\_ and ____ are at risk for staphylococcal scalded skin syndrome

Answer 28

Kids \< 5 years and adults with renal disease are at risk for staphylococcal scalded skin syndrome

Question 29

Wound cultures from erosions are ____ in staphylococcal scalded skin syndrome

Answer 29

Wound cultures from erosions are negative in staphylococcal scalded skin syndrome

Question 30

Scarlet fever is a ____ caused by \_\_\_\_

Answer 30

Scarlet fever is an exotoxin-triggered reaction with cutaneous manifestations caused by Group A Streptococcal pyrogenic exotoxins

Question 31

Scarlet fever usually occurs in ages \_\_\_

Answer 31

Scarlet fever usually occurs in ages 2-10 (rarely in adults)

Question 32

Scarlet fever is characterized by \_\_\_\_, diagnosed by \_\_\_\_, and treated using \_\_\_\_

Answer 32

Scarlet fever is characterized by exanthem followed by desquamation beginning at face and ending with hands and feet, diagnosed by positive strep culture from throat, treated using penicillin

Question 33

Cellulitis is \_\_\_\_, is caused by \_\_\_\_, and is commonly found on \_\_\_\_

Answer 33

Cellulitis is spreading erythematous tender plaque, is caused by Group A Strep / Staphylococcus aureus infection of the dermis, and is commonly found on the lower leg

Question 34

Cellulitis treatment involves \_\_\_\_

Answer 34

Cellulitis treatment involves beginning antibiotics immediately for coverage for Gram positive bacteria

Question 35

Erysipelas is \_\_\_\_

Answer 35

Erysipelas is superficial cellulitis with marked dermal lymphatic involvement, causing skin to be edematous or raised (lower extremities and face, Group A strep)

Question 36

Abscess is \_\_\_\_

Answer 36

Abscess is collection of pus within dermis and deeper tissues (painful / tender / fluctuant and erythematous nodules, often surmounted by a pustule and surrounded by a rim of erythematous edema, spontaneous drainage of purulent material may occur)

Question 37

Abscesses are treated with \_\_\_\_

Answer 37

Abscesses are treated with incision and drainage

Question 38

Folliculitis is most often caused by \_\_\_\_

Answer 38

Folliculitis is most often caused by Staphylococcus aureus (multiple small papules / pustules on an erythematous base that are pierced by a central hair although the hair may not always be visualized)

Question 39

Furuncle is \_\_\_

Answer 39

Furuncle is acute, round, tender, circumscribed perifollicular abscess that generally ends in central suppuration (usually caused by Staphylococcus aureus)

Question 40

Carbuncle is \_\_\_\_

Answer 40

Carbuncle is coalescence of several inflammed follicles into a single inflammatory mass with purulent drainage from multiple follicles (usually caused by Staphylococcus aureus)

Question 41

Describa anthrax

Answer 41

Anthrax * Caused by Bacillus anthracis * Large, boxcar shaped, Gram-positive, non-motile, spore-forming bacterial rod * Endemic to wild and domestic animals * Inhalational, gastrointestinal, and cutaneous

Question 42

Cutaneous anthrax is characterized by ____ and \_\_\_\_

Answer 42

Cutaneous anthrax is characterized by central ulceration and black eschar

Question 43

Secondary syphilis is similar to eruption of pityriasis rosea except there are additional ____ and \_\_\_\_

Answer 43

Secondary syphilis is similar to eruption of pityriasis rosea except there are additional lymphadenopathy and palm / sole involvement (lesions contain spirochetes so wear gloves, Treponema palldium)

Question 44

Syphilis testing involves ____ and is treated with \_\_\_\_

Answer 44

Syphilis testing involves RPR with prozone and is treated with intramuscular penicillin (prozone phenomenon on agglutination tests: antigen / antibody mismatch such that there is so much excess antibody that it clumps and leads to false negative, need to rerun test as serial serum dilutions)

Question 45

TB cutaneously presents as ___ or \_\_\_

Answer 45

TB cutaneously presents as lupus vulgaris or scrofuloderma (scrofuloderma: cold abscess and breakdown of overlying skin)

Question 46

Mycobacteria marinum presents as \_\_\_\_

Answer 46

Mycobacteria marinum presents as fish tank granuloma

Question 47

Mycobacterium leprosy is \_\_\_

Answer 47

Mycobacterium leprosy is chronic granulomatous infection especially of skin and nerves (leprosy / Hansen's disease)