Harvey's Garden

Skin and soft tissue infections

Properties2
tags—
aliases

3 min read

Overview

  • Skin and soft tissue infections (SSTIs) range from superficial bacterial infections to life-threatening deep tissue necrosis.
  • Key Step 2 CK objective: Differentiate superficial vs. deep infections and determine when urgent surgical intervention is required.

Bacterial Skin Infections

Impetigo

  • Etiology: S. aureus (MCC) or S. pyogenes (GAS).
  • Clinical Features:
    • Non-bullous: “Honey-colored” crusts on erythematous base, painful/pruritic, face/extremities.
    • Bullous: Flaccid bullae w/ clear/yellow fluid, ruptures leaving thin brown crust (mediated by S. aureus exfoliative toxin).
  • Tx:
    • Localized: Topical mupirocin.
    • Widespread: PO Abx (cephalexin, dicloxacillin).
  • Complication: Poststreptococcal glomerulonephritis (PSGN). Note: Tx of impetigo prevents PSGN transmission but does not prevent PSGN development in the affected pt (unlike rheumatic fever in strep pharyngitis).

Erysipelas vs. Cellulitis

  • Erysipelas:
    • Pathology: Upper dermis and superficial lymphatics. MCC is Streptococcus pyogenes. c
    • Risk factors:
      • Lymphatic obstruction (e.g., post-mastectomy, chronic lymphedema, venous insufficiency).
      • Local skin barrier breakdown (tinea pedis, venous stasis ulcers, insect bites, trauma).
      • Prior history of erysipelas.
      • Obesity.
    • PE: Well-demarcated, raised, bright red border, rapid onset, systemic symptoms (fever, chills) early. Often on face or lower extremity.
    • Tx: IV/PO penicillin, cephazolin, or cephalexin.
  • Cellulitis:
    • Pathology: Deep dermis and subcutaneous tissue. MCC is GAS or S. aureus (including MRSA).
    • PE: Ill-defined, flat, erythematous borders, warm, tender, fluctuance suggests abscess.
    • Tx:
      • Non-purulent (GAS): Cephalexin.
      • Purulent/Suspected MRSA: Clindamycin, TMP-SMX, doxycycline.
      • Severe/Systemic: IV vancomycin, linezolid, or daptomycin.

Abscess, Furuncles, & Carbuncles

  • Pathology: Wall of infection deep in dermis/hair follicles. MCC is S. aureus (often MRSA).
  • PE: fluctuant, painful nodule. Carbuncle = coalescence of several furuncles.
  • Tx:
    • Small (< 5 cm) without systemic symptoms: Incision & Drainage (I&D) alone.
    • Large (> 5 cm), systemic symptoms, or immunosuppressed: I&D + PO Abx (TMP-SMX or doxycycline).

Necrotizing Fasciitis

  • Pathology: Deep subcutaneous tissue and fascia necrosis. Polymicrobial (Type I) or Monomicrobial (Type II, GAS).
  • PE: Pain out of proportion to exam, rapid progression, crepitus, purple/blue skin discoloration, bullae, anesthesia of affected skin.
  • Dx: Clinical presentation is paramount. X-ray/CT showing gas in soft tissue is highly specific but non-sensitive. Do not delay Tx for imaging.
  • Tx: Urgent surgical debridement (emergent consult) + empiric broad-spectrum IV Abx (e.g., vancomycin + piperacillin-tazobactam or meropenem + clindamycin to inhibit toxin production).

Perianal streptococcal dermatitis

  • Etiology & Demographics:
    • Group A Streptococcus (GAS) (S. pyogenes); peak in children aged 6 months–10 years.
    • Common autoinoculation from recent GAS pharyngitis or household contacts.
  • Clinical Presentation: c
    • Sharply demarcated, bright red perianal erythema extending 2–3 cm from anal verge.
    • Intense pruritus, dyschezia (painful defecation), and blood-streaked stools.
    • Systemically well, afebrile (differentiates from perianal cellulitis/abscess).
  • Diagnosis:
    • Initial: Perianal rapid strep antigen test (RADT) swab.
    • Confirmatory/Gold Standard: Perianal skin swab culture (beta-hemolytic colonies).
  • High-Yield Differentials:
    • Candida: Involves intertriginous folds with satellite lesions; (+) KOH prep.
    • Pinworm (Enterobius): Nocturnal perianal pruritus, minimal erythema; (+) tape test.
    • Child Sexual Abuse: Lacerations extending beyond verge, contusions, purulent STI discharge.
  • Management:
    • 1st-line: Oral Penicillin V or Amoxicillin for 10–14 days.
    • Penicillin allergy: Cephalexin (non-severe) or Clindamycin (severe/IgE-mediated).
    • Exam Trap: Topical Abx alone are ineffective and lead to high recurrence rates.
    • Supportive: Stool softeners to treat/prevent withholding-induced constipation.
  • Complications & Board Pearls:
    • Voluntary stool withholding leading to secondary constipation and encopresis.
    • PSGN can occur following cutaneous GAS.
    • Acute Rheumatic Fever does NOT occur after cutaneous/perianal GAS (pharyngitis only).

Graph View

Backlinks