⚠️ Life-Threatening Emergencies
• Meningococcemia (N. meningitidis): petechial/purpuric rash, fever, septic shock → urgent antibiotics
• Rocky Mountain spotted fever: petechial rash (palms/soles), headache, tick exposure → doxycycline
• Kawasaki disease: fever ≥5 days, conjunctivitis, oral changes, rash, cervical adenopathy, extremity changes → IVIG, aspirin
🦠 Viral Exanthems
• Measles: 3Cs (cough, coryza, conjunctivitis), Koplik spots, head-to-toe morbilliform rash
• Rubella: pink macules, postauricular/occipital lymphadenopathy, arthralgia (older girls)
• Roseola (HHV-6/7): high fever 3-5 days → rash appears as defervescence, infants/toddlers
• Fifth disease (parvovirus B19): slapped cheeks → lacy reticular rash, aplastic crisis in hemolytic anemia
🩺 Bacterial & Other
• Scarlet fever (Group A Strep): sandpaper rash, Pastia lines, strawberry tongue, pharyngitis
• Erythema marginatum (rheumatic fever): serpiginous, evanescent, pale center, truncal, non-pruritic
• Lyme disease (erythema migrans): expanding bull's-eye rash at tick bite site ± flu-like symptoms
• Gianotti-Crosti (papular acrodermatitis): flat-topped papules face/buttocks/extensor surfaces, EBV most common
📋 Petechial/Purpuric Rashes
• Non-blanching = extravasated RBCs → concern for sepsis (meningococcus), vasculitis (HSP), platelet disorders (ITP)
• HSP: palpable purpura lower extremities/buttocks, arthralgia, abdominal pain, hematuria
• Enterovirus common cause of petechiae in well-appearing febrile child (after ruling out serious causes)
📌 Decision strategy: Fever + petechial/purpuric rash → immediate evaluation for meningococcemia. Kawasaki if fever ≥5 days with ≥4 of 5 criteria. Roseola: fever then rash. Measles: 3Cs + Koplik spots (pathognomonic).