Skin and Soft Tissue Infections

Question 1

Impetigo

Answer 1

pathology:
* intraepidermal vesicopustule
etiology:

• Group A Strep
• Staph aureus

epidemiology:

• all ages, most often kids (very communicable)
• hot, humid weather

O:

• face and extremities
• golden “stuck-on” crusts, not painful
• highly communicable

P/TX:

• PCNase resistant PCN ie dicloxacillin (this covers both staph and strep infection)
• PCN G, V
• Erythromycin

Question 2

Folliculitis

Answer 2

pathology:

• w/n hair follicules and apocrine sweat glands
• pruritic papule often w/ pustule

etiology:

• most common = Staph aureus
• can be Strep A (Strep pyogenes)

epidemiology:
* predisposing underlying conditions, ie DM, exposures (hot tub)

O:

• buttocks, axillae
• hair bearing areas
• tender
• surrounding erythema
• acute and/or chronic (recurrent)

P:

• problem for recurrence, one spreads to another
• get rid of all razors, perpetuating factors
• warm compresses
• topical abx
• in general just drain it out

Question 3

Furuncles

Answer 3

pathology:

• deep inflamm nodules developing from preceding folliculitis

etiology:

• Staph aureus

epidemiology:

• skin w/ hair follicles subject to friction and perspiration
• obesity, DM, use of corticosteroids (if on anti-inflamm, dont see as much redness and dont notice it)

O:

• firm, tender nodule which progresses to painful fluctuant lesion
• often drains spontaneously
• often look from a distance too
• warm
• firm
• surrounding, extending erythema

P/TX:

• proper I&D of abscess or other focal infections is mainstay of therapy and may be sufficient for cutaneous abscess
• for uncomplicated infections oral antimicrobial therapy is satisfactory
• can move to IV abx for more complicated infections

Question 4

Carbuncle

Answer 4

pathology:

• more extensive furuncle, extending to subQ fat
• multiple abscesses drain along hair follicles

etiology:

• Staph aureus

epidemiology:

• occur more often in nape of neck, back, back of thighs (thick, elastic skin)
• otherwise similar to furuncle

O:

• pt often acutely ill (fever/malaise)
• can be complicated by bacteremia or cellulitis
• can see lesions at different stages

P/TX:

• proper I&D of abscess or other focal infections is mainstay of therapy and may be sufficient for cutaneous abscess
• for uncomplicated infections oral antimicrobial therapy is satisfactory
• can move to IV abx for more complicated infections

Question 5

Ecthyma

Answer 5

pathology:

• starts intraepidermal, penetrates into epidermis and dermis

etiology:

• Group A Strep (primary or secondary due to trauma)

epidemiology:

• elderly and children, usually on LE

O

• “punched out” ulcers
• violaceous heaped borders w/ or w/o exudate
• clinically similar to lesions which occur in neutropenic pts w/ Pseudomonas bacteremia (ecthyma gangrenosa)
• surrounding erythema
• flaky skin (common in Strep infections)

Question 6

Erysipelas

Answer 6

pathology

• superficial cellulitis w/ lymphatic involvement

etiology

• Group A strep (Strep pyogenes)

epidemiology

• infants, kids, and elderly
• LE mostly and face
• occur at sites of trauma, ulcers, abrasions
• predisposing factors:
  
  • venous stasis/lymph obstruction
  • lymphedema secondary to radical mastectomy
  • DM, nephrotic syndrome and alcoholism

O:

• distinct, raised border (can feel drop off to normal skin
• painful, bright red lesion
• **advancing, raised border which is sharply demarcated from NL skin **
• fever is common
• up to 5% may have strep bacteremia
• potential to spread to **deeper **dermis
  
  • subQ abscesses
  • cellullitis
  • necrotizing fasciitis

P/TX:

• parenteral abx indicated for pts with facial erysipelas or evidence of systemic infection
• PCN is drug of choice
• initial therapy for pts w/ risk factors for Staph aureus should cover this strep

Question 7

Cellulitis

Answer 7

pathology

• spreading infection of skin involving the subQ tissues

etiology

• MOST COMMON
  
  • ​Group A strep
  • Staph aureus
• RARE
  
  • ​bacteremic seeding
• **OTHER **- epidemiologic clues…
  
  • ​Vibrio spp. (expsoure to warm sea water
  • Aeromonas sp. (exposure to fresh water)
  • Erysipelothrix sp. (handling of saltwater fish, shellfish, meats/hides)
  • Acinetobacter sp. (war wounds in Iraq and Afghanistan)

epidemiology

• occurs frequently at site of previous trauma (lac, puncture) or skin lesion (furuncle, ulcer)
• look for portal of entry e.g. Tinea pedis
• post-op wound infections
• IV drug use (skin “popping”)
• ass w/ sites of **abnormal lymph drainage **(SV grafts, radiation therapy, peripheral vascular disease)
• often RECURRENT

O:

• acute
• **rapid development of local tenderness **
• **site is erythematous, swollen and warm to touch **
• often ass w/ fever, chills and malaise
• border NOT well demarcated
• commonly ass w/ lymphangitis
  
  • **​look for lymphangetic streaking **(can see streaking up leg)
• **local abscess may develop **(should be drained)
• overlying necrosis may develop

A:

• DX by hx and PE
• cx of skin/wound useful when:
  
  • suspect unusual/abx-resistant pathogens
  • failed course of empiric therapy
  • fluctuant areas present or there are bullae

P/TX:

• most therapy is EMPIRIC as it is rare to id a causative organism
• THERAPY - supportive (elevation) and abx (IV vs oral)
  
  • PCN G, V
  • erythromycin
  • PCNase resistant PCN

Question 8

Necrotizing Fascitis

Answer 8

pathology:

• involves subQ soft tissues including the superficial and deep fascia

etiology:

• TYPE I
  
  • polymicrobial infection
  • anaerobes - commonly Bacteroides or Peptostrep spp
  • w/ one or more facultative anaerobes
    
    • E coli, Enterobacter, Klebsiella
    • Strep non Group A
    • Vibrio sp (exposure to warm sea water)
    • Pseudomonas (immunocompromised, IVDU)
    • Acinetobacter sp (OEF/OIF war wounds)
• TYPE II
  
  • Group A Strep
  • Alone or polymicrobial (often Staph aureus)

epidemiology:

• usually at site of trauma (lac, burn, abrasion, bite), also post-op
• any part of body, over half in LE
• DM (30%), PVD, alcoholism and IV drug use, skin “popping”
• Scrotum/perineum - Fournier’s gangrene

O:

• acute and/or subacute presentation (NSAIDS)
• starts - diffuse redness, warm, and is very tender
• progresses rapidly (hours to days)
  
  • fluid filled bullae (purplish-blue)
  • cutaneous necrosis
  • crepitus (subQ gas - polymicrobial)
  • pain out of proportion to physical findings
• loss of pain may be due to deeper injury
  
  • due to loss of superficial nerves secondary to thrombosis of small blood vessels in skin

Complications:

• compartment syndrome due to swelling and edema, may require fasciotomy
• systemic toxicity w/ hihg fever/leukocytosis
• blood cx often positive
• hypocalcemia w/ necrosis of subQ fat

P/TX:

• early recognition and TX
  
  • prompt surgical intervention
  • high overall mortality (worst in DM)
  • early DX leads to decreased mortality
• PCN G,V, erythromycin, PCNase resistant PCN
• add Clindamycin

Question 9

Clostridial Myonecrosis

“Gas Gangrene”

Answer 9

pathology:

• skeletal muscle necrosis due to histotoxic Clostridia spp.
• muscle disintegrates (coagulation necrosis)
• pale edematous on inspection, when cut does not bleed

etiology:

• C. perfringens in 80-90%
  
  • alpha Toxin
  • often find as contaminant in wounds, low incidence of infection
  • lower inoculum needed for devitalized tissues/FBs

epidemiology:

• contamination w/ SOIL or material 2/ Clostridial spores
• trauma (compound fx)
• war wounds
• post-surgical (bowel, biliary tract surgery)
• spontaneous, non-traumatic (bacteremia)

S/O:

• LIFE THREATENING
• incubate 1-2 days and rapidly progressive - hours
• PAIN is often severe, important early sign (sudden onset rapidly increasing pain in affected area)
• XR may see subQ air
• toxic appearance - shock and renal failure follow
• sudden onset hypotension, tachycardia
• fever, delirium/stupor (esp in last stages)
• local tenderness, tense edema, crepitus
• skin bronzed w/ dark green-black area of necrosis and fluid-filled blebs
• d/c serosanguinous, dark color (“coca-cola”); foul odor +/- gas bubbles

A:

• radiographic studies may show gas w/n soft tissues
• anaerobic cx confirms DX
• DDX: other bacteria can produce gas infected tissues

P/TX:

• prompt surgical evaluation and abx
• adequate surgical debridement and exposure of infected areas are essential w/ radical surgery often necessary
• IV PCN is effective
• Clindamycin may decrease production of bacterial toxin
• hyperbaric O2 therapy has been used empirically