Differential Diagnosis for Unilateral Erythematous Vesicular Leg Rash

Primary Diagnostic Considerations

Impetigo or bullous impetigo can present as vesicular lesions that become pustular, typically on exposed areas like legs, with Staphylococcus aureus or Streptococcus pyogenes as typical pathogens, according to the American Academy of Pediatrics 1
Staphylococcus aureus or Streptococcus pyogenes are typical pathogens for impetigo, as stated by the Infectious Diseases Society of America 2
Hand-foot-mouth disease can occasionally present with atypical distribution, though typically bilateral, with small pink macules evolving to vesicles, according to the Centers for Disease Control and Prevention 3
Herpes simplex virus can cause localized vesicular eruption, particularly if inoculated through skin break, as noted by the American Academy of Pediatrics 4

Rocky Mountain Spotted Fever begins as blanching macules on ankles/wrists progressing to petechiae, not vesicles, and involves palms/soles, as described by the Centers for Disease Control and Prevention 5
Meningococcemia would present with rapidly progressive petechial/purpuric rash, not vesicular, with systemic toxicity, according to the Centers for Disease Control and Prevention 5
Kawasaki disease requires ≥5 days fever plus polymorphous exanthem (not vesicular), conjunctivitis, oral changes, and other criteria, as stated by the American Heart Association 5

Bacterial culture is indicated if pustular, honey-crusted, or concern for impetigo, as recommended by the Infectious Diseases Society of America 2
Viral PCR/culture is indicated if vesicular fluid present and viral etiology suspected, according to the American Academy of Pediatrics 4

For suspected impetigo, topical mupirocin for localized disease, and oral antibiotics (cephalexin, dicloxacillin) if extensive, as recommended by the Infectious Diseases Society of America 2
For suspected viral infection, supportive care for HFMD, and consider acyclovir if HSV suspected and immunocompromised, according to the American Academy of Pediatrics 4

Do not delay bacterial culture if any purulent component or honey-crusting present, as emphasized by the Infectious Diseases Society of America 2
Do not miss systemic illness, if fever, petechiae, or toxic appearance present, immediately consider life-threatening conditions like meningococcemia or RMSF, as stated by the Centers for Disease Control and Prevention 5