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Dermatology USMLE Step 3 > SEction 2: Skin Infections and STDs > Flashcards

SEction 2: Skin Infections and STDs Flashcards

1
Q

Examples of skin fungal infections

A

Tinea pedis

Tenia corporis

Tinea capitia

Tinea cruris

Tinea versicolor

Onychomycosis

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2
Q

Skin fungal infections

Best initial test

Most accurate test

A

Potassium hydroxide (KOH) test of the skin. The leading edge of the lesion on the skin or nails is scraped with a scalpel to remove some of the epithelial cells or some of the nail and hair. KOH has the ability to dissolve the epithelial cells and collagen of the nail but not the fungus

Culture the fungus. Molds that grow on the skin (dermatophytes) take up to 6 weeks to grow, even on specialized fungal media. A specific species usually does not need to be isolated in most cases, unless the infection is of the hair or nails

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8763-8768). Kaplan Publishing. Kindle Edition.

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3
Q

Rx of onychomycosis (nail infection) or tinea capitis (hair infection)

Duration of fingernail infections

Duration of toe infections

A

Oral terbinafine or itraconazole

6 weeks

12 weeks

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4
Q
  1. Test to do when on terbinafine
  2. Why?
  3. Efficacy of griseofulvin compared to terbinafine
A
  1. LFT periodically
  2. Potentially hepatotoxic
  3. Griseofulvin is less efficacious than terbinafine; use is for 6 to 12 months at least
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5
Q

Rx of fungal infections of the skin not involving the nails and hair

A
  • Ketoconazole
  • Clotrimazole
  • Econazole
  • Terbinafine
  • Miconazole
  • Sertaconazole
  • Sulconazole
  • Tolnaftate
  • Naftifine

There is no clear difference in efficacy or adverse effects among them when they are used topically.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8776-8786). Kaplan Publishing. Kindle Edition.

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6
Q

Adverse effect of ketoconazole

A
  • Hepatotoxicity
  • Gynecomastia

This is why ketoconazole is not a good choice for onychomycosis.

There is no topical form of fluconazole. Fluconazole also has less efficacy for dermatophytes of the nails when used systemically.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8776-8786). Kaplan Publishing. Kindle Edition.

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7
Q

List the bacterial infections of the skin

A

Impetigo

Erysipelas

Cellulitis

Folliculitis

Furuncles

Carbuncles

Necrotizing fascitis

Paronychia

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8
Q

Rx of bacterial skin infections in general

  • Impetigo
  • Erysipelas
  • Cellulitis
  • Folliculitis
  • furuncles
  • Carbuncles
A
  1. Dicloxacillin, cephalexin (Keflex), or cefadroxil (Duricef)
  2. The intravenous equivalent of dicloxacillin is oxacillin or nafcillin.
  3. The intravenous equivalent of cefadroxil is cefazolin

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8795-8810). Kaplan Publishing. Kindle Edition.

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9
Q

Rx of skin infections if patient reacts only by rash to penicillin

A

Cephalosporins can be safely used. There is far less than 1 percent cross-reaction between penicillins and cephalosporins. (The cross-reactivity is actually estimated to be 0.1 percent.)

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8795-8810). Kaplan Publishing. Kindle Edition.

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10
Q

Rx of bacterial skin infections when there is anaphylactic reaction to penicillins

A

If the penicillin reaction is anaphylaxis, cephalosporins cannot be used. The alternative antibiotics that will treat the skin are macrolides or newer fluoroquinolones

  • Erythromycin
  • Azithromycin
  • Clarithromycin
  • Levofloxacin
  • Gatifloxacin
  • Moxifloxacin
  • Vancomycin (IV)

Ciprofloxacin will not adequately cover the skin

Vancomycin is only for intravenous use for skin infections. Oral vancomycin is not absorbed and is used only for Clostridium difficile intestinal infection.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8795-8810). Kaplan Publishing. Kindle Edition.

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11
Q

Indication for IV vancomycin in bacterial skin infection

Oral equivalent of IV vancomycin

A

Methicillin-resistant Staphylococcus aureus (MRSA)

  • Nursing home patient
  • Patient who has been in the hospital for a long time

Linezolid or bactrim

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8795-8810). Kaplan Publishing. Kindle Edition.

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12
Q

Impetigo

This is a superficial bacterial infection of the skin limited largely to the epidermis and not spreading below the dermal-epidermal junction. The infection is described as “weeping,”“oozing,”“honey-colored,” or “draining.” It occurs more often in warm, humid conditions, particularly when there is poverty and crowding of children. It is both contagious and autoinoculable. Impetigo can cause glomerulonephritis, but it will not cause rheumatic fever.

  1. List the causes
  2. Best initial Rx
  3. Alternative Rx

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8812-8822). Kaplan Publishing. Kindle Edition.

A
  1. Causes of impetigo:
    • Staphylococcus aureus
    • Streptococcus pyrogenes (Group A Streptococcus)
  2. Topical antibiotics (mupirocin)
  3. Oral antibiotics should be used.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8812-8822). Kaplan Publishing. Kindle Edition.

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13
Q

Erysipelas

Erysipelas involves both the dermis and epidermis

  1. Most common cause
  2. Common clinical presentation
  3. Rx
  4. Rx if culture confirms Streptococcus as causative organism

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8824-8830). Kaplan Publishing. Kindle Edition.

A
  1. Group A Streptococcus (pyogenes)
  2. CF features
    • Fever
    • Chills
    • Bacteremia
    • Bright red, angry, swollen appearance to the face
  3. Systemic oral or intravenous antibiotics
  4. Penicillin G or ampicillin

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8824-8830). Kaplan Publishing. Kindle Edition.

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14
Q

Cellulitis

Cellulitis is treated with the antibiotics previously described, based on the severity of the disease. If there is fever, hypotension, or signs of sepsis or if oral therapy has not been effective, then the patient should receive intravenous therapy

List them

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8833-8845). Kaplan Publishing. Kindle Edition.

A
  • Oxacillin
  • Nafcillin
  • Cefazolin

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8833-8845). Kaplan Publishing. Kindle Edition.

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15
Q

Folliculitis, Furuncles, and Carbuncles

These 3 disorders represent 3 different degrees of severity of staphylococcal infection occurring around a hair follicle. As folliculitis worsens from a simple infection superficially around the hair follicle, it becomes a small collection of infected material known as a furuncle. When several furuncles become confluent into a single lesion, it becomes known as a carbuncle, essentially a localized skin abscess that must be drained.

  1. Causative organism in those who contract it from whirlpool or hot tub
  2. Of the three conditions, which is tender and which is nontender
  3. Rx for folliculitis
  4. Rx for furuncles and carbuncles
A
  1. Pseudomonas
  2. Folliculitis is rarely tender, while furuncles and carbuncles are extremely tender
  3. Topical mupirocin
  4. Dicloxacillin or cefadroxyl

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8833-8845). Kaplan Publishing. Kindle Edition.

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16
Q

Necrotizing Fascitis

This is an extremely severe, life-threatening infection of the skin. It starts as a cellulitis that dissects into the fascial planes of the skin

  1. List the most common causes
  2. True or False: diabetes increases the risk of developing fascitis
A
  1. ** Streptococcus** and Clostridia
    • they produce a toxin that worsens the damage to the fascia.
  2. True. Diabetes increases the risk of developing fasciitis

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8851-8861). Kaplan Publishing. Kindle Edition.

17
Q

Features of necrotizing fascitis

A
  • Very high fever
  • Portal of entry into the skin
  • Pain out of proportion to the superficial appearance
  • Bullae
  • Palpable crepitus

If presented with an obvious clinical case with crepitus, pain, high fever, and a portal of entry, answer surgery, not a test, such as x-ray, as the best initial step.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8855-8861). Kaplan Publishing. Kindle Edition.

18
Q

Rx of necrotizing fascitis

Mortality rate in necrotizing fascitis

A

Beta lactam/ beta lactamase combination medications:

  • Ampicillin/ sulbactam (Unasyn)
  • Ticarcillin/ clavulanate (Timentin)
  • Piperacillin/ tazobactam (Zosyn)

If there is a definite diagnosis of group A Streptococcus (pyogenes), then the treatment is with

  • Clindamycin and penicillin

Without adequate therapy, necrotizing fasciitis has an 80 percent mortality.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8863-8875). Kaplan Publishing. Kindle Edition.

19
Q

Paronychia

This is an infection loculated under the skin surrounding a nail.

Rx?

A
  1. Incision and drainage
  2. Antistaphylococcal antibiotics:
    • Dicloxacillin
    • Cepahlexin
    • Cefadroxyl

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8876-8884). Kaplan Publishing. Kindle Edition.

20
Q

Herpes Simplex

Herpes simplex infections of the genitals are characterized by multiple, painful vesicles. They are usually obvious by examination, and you should proceed directly to therapy with acyclovir, famciclovir, or valacyclovir.

  1. Best initial test
  2. Most accurate test
A

The most common wrong answer is serology. Serology is not a useful test for diagnosing acute herpes infections.

  1. Tzanck smear. The Tzanck smear is somewhat nonspecific in that it will only determine that the infection is in the herpes virus family. Tzanck smears detect multinucleated giant cells and are similar in technique to a Pap smear. A scraping of the lesion is immediately placed on a slide and sprayed with fixative.
  2. Viral culture. This grows in 24– 48 hours.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8881-8892). Kaplan Publishing. Kindle Edition.

21
Q

Rx of herpes simplex

A
  • Oral acyclovir, famciclovir, or valacyclovir
  • Topical acyclovir has extremely little efficacy.
  • Topical penciclovir has some utility for oral herpetic lesions, but it must be used every 2 hours.
  • The treatment of acyclovir-resistant herpes is with foscarnet.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8894-8896). Kaplan Publishing. Kindle Edition.

22
Q

Complications of Herpes zoster

A
  • Pneumonia
  • Hepatitis
  • Dissemination
23
Q

Rx of herpes zoster

A
  • Steroid use is still not clearly beneficial, although the best evidence for its efficacy is in elderly patients with severe pain.
  • The rapid administration of acyclovir still has the best efficacy for decreasing the risk of postherpetic neuralgia.
  • Other treatments for managing the pain:
    • Gabapentin: The most effective analgesic specifically for postherpetic neuralgia
    • Tricyclic antidepressants
    • Topical capsaicin
  • Nonimmune adults exposed to chickenpox should receive varicella zoster immune globulin within 96 hours of the exposure for it to be effective.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8912-8923). Kaplan Publishing. Kindle Edition.

24
Q

Human Papillomavirus (HPV) Warts caused by HPV, or condylomata acuminata

A

Mechanical removal: This can involve cryotherapy with liquid nitrogen, laser removal, or trichloroacetic acid or podophyllin to melt them away.

Imiquimod is a local immunostimulant that takes several weeks to result in sloughing off of the wart. Resolution is slower; however, there is never any damage to the surround normal tissue and no pain.

Podophyllin is potentially teratogenic and should be scrupulously avoided in pregnancy.

Fischer, Conrad (2012-09-22). Master the Boards: USMLE Step 3 (Kaplan Medical Usmle Master the Boards Step 3) (Kindle Locations 8924-8935). Kaplan Publishing. Kindle Edition.

25
Q

Best initial diagnosis for primary syphilis

Best initial diagnosis for secondary syphilis

A

Dark field examination

VDRL and RPR

26
Q

Rx of primary and secondary syphilis

Alternative Rx in case of allergy

A

IM Penicillin

Doxycycline orally for 2 weeks

27
Q

List those in which outbreaks of shingles (dermatomal herpes zoster) occur more frequently

A
  • Elderly
  • Leukemia patients
  • Lymphoma patients
  • HIV patients
  • Those on steroids

Generally those with defect in the lymphocytic portion of the immune system

Dermatology USMLE Step 3 (4 decks)

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