Skin Infections, Infestations, and Systemic Disease

Question 1

Identify peptides involved in innate immunity of the skin

Answer 1

Alpha defensins are particularly abundant in neutrophils, certain macrophage populations and Paneth cells of the small intestine. Defensins enhance phagocytosis, promote neutrophil recruitment, enhance the production of proinflammatory cytokines, suppress anti-inflammatory mediators and regulate complement activation - upregulate innate host inflammatory defenses against microbial invasion.

Other skin defense mechanisms include:

• Physical Barrier
• Desquamation
• Localized immune response (cellular and immunoglobulin)
• skin pH

Question 2

For common cutaneous viral infections, recognize the clinical characteristics and identify the etiologic agent.

Answer 2

a. Human Papillomavirus

• Clinical: warts (verruca vulgaris) - body’s own skin proliferating
• Etiology: virus acquired through breaks in skin/mucosa transmitted person to person, 10% of kids have it

b. Herpes Simplex Virus

• Clinical: grouped blisters/vesicles on a red base, atypical presentation in immunocompromised pts.
• Etiology: virus acquired thorugh breaks in skin or mucosa (saliva, vaginal secretions, vesicular fluid, direct skin contact)

c. Varicella Zoster Virus

• Clinical: chicken pox (varicella) = fever, single thin-walled vesicle on erythematous base (dew drop on a rose pedal), new stages of lesions for 3-5 days; shingles (zoster) grouped vesicles on erythmatous base on dermatome
• Etiology: 90% of adults have antibodies, spread by respiratory route, zoster is viral reactivation

Question 3

For common cutaneous bacterial infections, recognize the clinical characteristics and identify the etiologic agent

Answer 3

a. Impetigo

• Clinical: typically affects face in children - honey colored yellow crust, can have bullous, mild lymphadenopathy, 5% associated w/ post strep. glomerulonephritis
• Etiology: Strep. pyogenes or Staph. aureus; most common superficial bacterial infx in children, more common in humid areas, with poor hygiene, acquired by person to person contact

b. Cellulitis

• Clinical: Erysipelas confied to face is erythematous and has cliff-drop borders, may or may not have lymphadenopathy. Lymphatic streaking is common.
• Etiology: infx occur through skin breaks. strep and staph typical. Common in very young, elderly, immuno-compromised, pts with chronic ulcers

c. Syphilis

• Clinical: primary lesion is indurated skin ulcer that is painless (chancre), lymphadenopathy in 90% of pts, rash on palms/soles of feet, anular plaque, non-pruritic papulosquamos lesions, alopecia, ora lesions
• Etiology: Treponema pallidum, increasing in incidence, STD, can’t culture it

Question 4

For common cutaneous fungal infections, recognize the clinical characteristics and identify the etiologic agent.

Answer 4

a. Dermatophyte Infections (Ring Worm)(eat keratin in skin, hair, nails)

• Clinical: ring worm anular plaque with central clearing, athlete’s foot, can be dry feeling, lymphadenopathy, black dots in hair follicles, grey patch in hair,
• Etiology: Trichophyton, Epidermophyton, Microsporum, locker rooms (humid), soil, sharing clothes, cats, cattle

b. Candidiasis (thrush)

• Clinical: affect mucous membranes and skin, thrush, rash with satellite pustules
• Etiology: Candida, normal flora, increased prevalence in: diabetes, occlusion, immunocompromised, corticosteroid use, broad spectrum antibiotics

c. Tinea (Pityriasis) Versicolor (Athlete’s Foot)

• Clinical: trunk, asymptomatic, tan-colored subtly scaly macule or patch
• Etiology: Malassezia furfu, humid and warm climates, confined to post-pubertal patients

Question 5

For common skin infestations, recognize the clinical characteristics and identify the etiologic agent.

Answer 5

a. Scabies

• Clinical: papules with burrows and genital nodules, common in web spaces, genitals, sock line, under bra, very itchy (pruritus)
• Etiology: Sarcoptes scabei var hominis, 0.3 mm, usually less than 100 per host, person to person contact, highest prevalence in children and sexually active adults

b. Lice Infestation

• Clinical: egg casings on hair, excoriation and redness of scalp, erythematous papules and macules, intense itching (pruritis)
• Etiology: 3 different organisms depending on the body area; Scalp louse = Pediculus humanaus var capitis, body = var. corporis, pubic = var. pubis

Question 6

Explain the clinical utility and indications for the following diagnostic procedures in dermatologic patients:

Answer 6

a. Tzanck smear

• take a blade, scrape blister base and examine on a microscopic slide
• used for viral disease such as Herpes Simplex Virus, confirm by noting giant multinucleated cells

b. Gram Stain

• delineates type of bacteria based on cell wall structure
  
  • gram + = darker purple
  • gram - = pink

c. KOH Prep
* used to kill human material on biopsies thereby leaving fungal parasites visible for study
d. Wood’s light exam
* application of tetracycline solution followed by shining a wood’s light will accentuate the burrow of scabies mites
e. Mineral Oil (Wet Prep) for scabies
* evident mites, eggs or feces on biopsy and clinically pt. is itchy with S shaped burrows and/or genital nodules
f. Darkfield
* essentially a blacklight used to diagnose syphylis b/c syphilis cannot be cultured, will appear as spirochete corkscrew organism