Cutaneous infections

Question 1

Impetigo:

Answer 1

• Most common cause is S. aureus.
• Rash usually begins on face; vesicles and pustules rupture to form honey-colored, crusted lesions.
• Highly contagious (direct contact).
• Bullae commonly occur.

Question 2

Staphylococcal scalded skin syndrome:

Answer 2

• Toxin-mediated type of exfoliative dermatitis, primarily affects infants and children.
• S. aureus exotoxins: ET-A, ET-B. Cause intraepidermal splitting through the granular layer by targeting desmoglein 1 (in stratum granulosum).
• Fever, large flaccid bullae, erythematous rash.

Question 3

Cellulitis (deep pyogenic infection):

Answer 3

• Diffuse inflammation of the connective tissue of the skin and/or the deeper soft tissues.
• B-hemolytic streptococci and/or coagulase positive staphylococci.
• Legs most commonly affected.

Question 4

Erysipelas:

Answer 4

• Bacterial skin infection involving the superficial cutaneous lymphatics (unlike cellulitis, which is deep).
• Sharply outlined edematous, erythematous, tender, and painful plaque on face or lower extremities.
• S. pyogenes is the most common organism.

Question 5

Verrucae:

Answer 5

• Most warts are caused by low-risk HPV.
• High-rish HPV also exists.
• Verrucous epidermal hyperplasia.
• Koilocytosis of the upper layer of epidermis.
• Infected cells show keratohyaline granules and intracytoplasmic aggregates.

Question 6

Condyloma accuminatum:

Answer 6

• Genital warts.
• Caused by HPV 6 and 11; high-risk HPV types may increase the risk for cancer.
• Single or multiple papular lesions that are pearly, filiform, fungating, cauliflower, or plaque-like.

Question 7

Herpes simplex virus:

Answer 7

HSV-1: Common in childhood, lips

HSV-2: STD

Question 8

VZV (chickenpox):

Answer 8

• Highly contagious and spread through respiratory route.
• Rash progresses form macules to vesicles to pustules (**all stages are simultaneously present).
• Complication: Reye syndrome (giving aspirin during viral infection; associated with fatty liver and cerebral edema).

Question 9

VZV (shingles):

Answer 9

• Reactivation of latent VZV infection.

- Rash has unilateral dermatomal distribution.

Question 10

Herpes virus (HSV and VZV) general features:

Answer 10

• Acantholysis of epidermis.
• Multinucleated keratinocytes with intranuclear inclusions (Cowdry Type A inclusions).
• Perineurial and intraneurial inflammation.

Question 11

Herpes diagnosis:

Answer 11

Tzank smear (stain with Giemsa stain)

More sensitive: viral culture

Question 12

Molluscum contagiosum:

Answer 12

• Caused by DNA poxvirus.
• Children: acquire it through close contact.
• Immunosuppressed (HIV) patients.
• STD
• Histology shows inverted “crater-like” nodule with eosinophilic cytoplasmic bodies.

Question 13

Scabies:

Answer 13

• Caused by the mite Sarcoptes scabiei. Transmitted via prolonged direct human contact and rarely by fomites.
• Extremely pruritic papulovesicular eruption.
• Erupts 4 weeks after infestation.

Question 14

Dermatophytosis:

Answer 14

• AKA tinea.
• 3 genera:
  1. Microsprum
  2. Epidermophyton
  3. Trichophyton
• Scaly, erythematous plaques, often annular.
• Diagnosis: KOH prep.
• Variations: capitis, corporis, barbae, cruris, pedis.

Question 15

Tinea versicolor:

Answer 15

• Tropical climate, young adults.
• Caused by Malassezia globosa.
• Multiple irregular areas of hypo or hyperpigmentation, which are circular and macular.
• “Spaghetti and meatballs” morphology.