Infectious Disease Manifestations

Question 1

Tx of Dermatitis herpetiformis

Answer 1

Looks like HSV but it’s NOT

Give dapsone and gluten-free diet

Question 2

Cellulitis

Answer 2

Infection of soft tissue of the skin. It extends from dermis into subq tissue. The skin is warm, red, swollen, and tender

Cellulitis involves legs more often than arms. Does not have collections of walled-off infection (that is an abscess).

Not only at hair follicle (that’s folliculitis, furuncles, carbuncles)

Dx - Most accurate test is to inject sterile saline into skin and aspirate it for culture. Yield is only 20%. Staph much more common than strep

Antistaph penicilins are OX-CLOX-DICLOX-NAF

Skin infection is staph aureus not S.epi. Epi just lives on the skin.

Question 3

Necrotizing fasciitis

Answer 3

Deep infection along a fascial plane causing severe pain followed by anesthesia. Infection is caused by S.pyogenes (10%) or commonly by a mixed infection of anaerobic and aerobic bacteria that include S aureus, E Coli and C.pergringens.

A hx of trauma or recent surgery to affected area is often but not always given.

Most important signs are tissue necrosis, putrid discharge, bullae, severe pain, gas production. rapid burrowing through fascial planes, lack of classical tissue inflammatory signs and intravascular volume loss

Fournier gangrene is a form of nec fas localized to genital and perineal areas

Dx - CT shows air in tissue. Bx from edge can be diagnostic

Tx - surgical emergency. Early and aggressive surgical debridement.

If strep is organism then penicillin G is treatment of choice. Clindamycin is second line. For anaerobic coverage give metronidazole or a third gen cephalosporin. In most cases, broad spectrum is needed.

Question 4

Folliculitis vs furuncle vs carbuncle

Answer 4

Folliculitis is inflammation of hair follicle. When deeper an abscess of hair follicle forms (Furuncle). Furuncle can spread to adjacent follicles (carbuncle)

Question 5

Tx of folliculitis

Answer 5

Topical ABx can be used to treat mild disease (usually staph, strep or gram neg, sometimes candida)

Severe cases (fever, bacteremia, chills) require systemic ABx. Large lesions must be incised, drained and cultured to rule out MRSA

Question 6

Pilonidal cyst

Answer 6

Abscesses in sacrococcygeal region that usually occur near top of natal cleft.

Not all contain hair and not all are true cysts.

Repetitive trauma to the region plays a role.

Condition thought to start as a folliculitis that becomes an abscess complicated by perineal microbes, esp Bacteroides. Age 20-40. Men more than women.

Tender, fluctuant, warm, indurated and sometimes associated with purulent drainage or cellulitis. Systemic symptoms uncommon, but cysts may develop into perianal fistulas.

Risk factors - deep and hairy natal cleft, obesity, sedentary life

Dx - clinical. Rule out perirectal and anal abscess

Tx - I and D of abscess under local anesthesia followed by sterile packing of wound. Good local hygiene and shaving of region can help prevent recurrence. Follow up with a surgeon.

Abx are NOT needed unless cellulitis is present. If it comes down to ABx you need one that covers aerobic and anaerobics

Question 7

Best initial test for any tinea

Answer 7

KOH prep. It will dissolve epidermal skin cells and leave the fungi intact so they can be seen

Question 8

Most accurate test for any tinea

Answer 8

Fungal Cx

Question 9

Best initial therapy for any tinea

Answer 9

Topical antifungal agent if no hair or nails are involved

Question 10

Best initial therapy for hair and nail infections of tinea

Answer 10

Terbinafine. Itraconazole is close in efficacy too.

Question 11

What is important to remember about ketoconazole?

Answer 11

It is antiandrogenic. Will cause gynecomastia

Question 12

Where do dermatophytes live?

Answer 12

Only in tissues with keratin

Question 13

What are the dermatophytes?

Answer 13

Most common worldwide is Trichophyton rubrum.

Also microsporum, trichophyton, and epidermophyton

Question 14

Which tinea must be treated with systemic drugs?

Answer 14

Tinea capitis. Also consider systemic drugs in any tinea in someone who is immunocompromised

Question 15

Lice

Answer 15

Live off blood and on specific parts of body, depending on species. Spread through body contact or by sharing of bedclothes and other garments or hair accessories. Secrete local toxins that lead to itchiness

Public lice saliva has anticoagulant and turns bites blue

Dx - visualize them in hair or clothes

Tx
1) Head lice - treat with OTC pyrethrin, benzyl alcohol, and mechanical removal of nits

2) Body lice - Wash body, clothes, and bedding thoroughly. Treating the body with topical permethrin or pyrethrin may also be needed
3) Public lice - pyrethrin

Question 16

Scabies

Answer 16

Caused by sarcoptes scabiei. Burrowing of this arthropod into epidermis leads to itching that increases in intensity once allergy to mite or its products develops. Scabies spread through close contact.

History and exam

1) Intense itching esp at night and after hot showers. Red, pimple like papules with linear tracks, representing the burrows of the mite
2) The most commonly affected sites are the hands (spaces between knuckles), axilla, genitals
3) Secondary bacterial infection is common

Dx - History of itchiness in several family members is suggestive. Mite may be identifiable by scraping an intact tunnel and looking under microscope

Tx
1) Patients should be treated overnight with 1-2 applications of 5% permethrin from neck down and their contacts should be treated as well. Oral ivermectin also effective

2) Itchiness may persist for 2 weeks after treatment, so symptomatic tx should be provided

Question 17

Treatment for cellulitis, folliculitis, furuncles, and carbuncles

Answer 17

Mild disease: Use oral meds

1) Dicloxacillin, cephalexin, cefadroxyl
2) Penicillin allergic: erythromycin, clarithrimycin, clindamycin
3) MRSA: doxycycline, clindamycin, TMP/SMX

Severe diseaes (fever): Use IV meds

1) Oxacillin, nafcillin, cefazolin
2) Penicillin allergy: Clindamycin, vancomycin
3) MRSA - vancomycin, linezolid, daptomycin, tigecycline, ceftaroline

Cross rxn btw penicillins and cephalosporins is unusual (less than 5%)

Question 18

Tx of impetigo

Answer 18

Mild - topical agents

1) Mupirocin
2) Retapamulin
3) Bacitracin

Severe - oral agents

1) Doxycycline
2) Clindamycin
3) TMP/SMX

Question 19

Erysipelas

Answer 19

Much more severe than impetigo bc it occurs at deeper level of skin. Much more often from strep than staph. Invades dermal lymphatics and causes bacteremia, leukocytosis, fever, chills

Untreated can be fatal

Look for bright red, hot swollen, lesion on face. Leukocytosis can occur bc it is more often a systemic disease

Tx - Although it is usually from strep, you may treat for staph as well unless you have definitive diagnositc test such as blood cultures