Categorize rash by morphology (macular/maculopapular, vesiculobullous, petechial/purpuric, urticarial) + fever + distribution + age. Petechiae below the nipple line + fever = meningococcemia. Mucosal involvement = consider SJS/TEN, Kawasaki, MIS-C.
🚩 Red-flag clues (must not miss)
- •Petechiae / purpura + fever = meningococcemia / RMSF / MIS-C
- •Mucosal sloughing + fever = SJS/TEN — stop offending drug, transfer to burn center
- •Target lesions + 2+ mucosal sites = erythema multiforme major
- •Fever ≥ 5 d + bilateral non-purulent conjunctivitis + rash + extremity changes + cervical LAD = Kawasaki
- •Honey-crusted bullae + sepsis = staph scalded skin
Differential & next step
| Diagnosis | Clue | Next step |
|---|---|---|
| Viral exanthem (most common) | Morbilliform, mild, well | Symptomatic |
| Measles | Cough/coryza/conjunctivitis + Koplik spots → cephalocaudal rash | Vit A; isolation; report |
| Roseola (HHV-6) | High fever × 3 d → rash appears AS fever resolves | Symptomatic |
| Erythema infectiosum (Fifth/B19) | Slapped-cheek, lacy rash on extremities | Symptomatic; avoid pregnant contacts |
| Hand-foot-mouth (coxsackie) | Vesicles palms/soles/mouth | Hydration, magic mouthwash |
| Scarlet fever (GAS) | Sandpaper rash, Pastia lines, strawberry tongue | PCN/amox × 10 d |
| Varicella | Crops of vesicles in different stages | Acyclovir if ≥ 12 y, immunocompromised, chronic skin/lung dz |
| HSP (IgA vasculitis) | Palpable purpura buttocks/legs + arthritis + abd pain + nephritis | UA, BP, supportive; steroids for severe abd/renal |
| Meningococcemia | Petechiae/purpura + fever + ill | EMERGENCY: ceftriaxone, droplet, PEP contacts |
| Kawasaki | ≥ 5 d fever + 4 of 5 criteria | Echo, IVIG 2 g/kg, ASA |
| Staph scalded skin (SSSS) | Tender erythroderma → bullae → desquamation, Nikolsky+ | Anti-staph (oxacillin/clindamycin), fluids |
| Stevens-Johnson / TEN | Drug, mucositis, sloughing > 10–30% | Stop drug, transfer burn unit |
| Urticaria | Wheals < 24 h each | Antihistamines; epi if anaphylaxis |
| Atopic dermatitis | Flexural, chronic, family hx atopy | Emollients + low-potency TCS |
| Tinea corporis | Annular, scaly, central clearing | Topical clotrimazole |
| Scabies | Burrows web spaces, intense itch night, family | Permethrin 5% (see scabies topic) |
| Impetigo | Honey-colored crust | Topical mupirocin or PO cephalexin |
Management / next steps
- Determine morphology + distribution + fever + ill vs well
- Petechiae + fever or any toxic appearance → labs, blood cx, empiric ceftriaxone, admit
- Mucosal involvement / Nikolsky+ → derm + burn-unit consult
- Non-blanching + abdominal pain in school-age child → think HSP
Pearls
- Use the Petechiae-in-the-Crying-Child rule: petechiae below the nipple line is more concerning than above (above can be from forceful crying/cough).
Source: https://fprmed.com/fprmedcom/Pages/Derm/Pedi_Rashes.html
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