What are the differential diagnoses and initial management for an 11-year-old with a 1-day history of rash/bumps on hands and arms?

Differential Diagnoses for 11-Year-Old with 1-Day Rash on Hands and Arms

The most critical immediate consideration is Rocky Mountain Spotted Fever (RMSF) or other tickborne rickettsial diseases, which can be fatal within 9 days if untreated, even without a reported tick bite. 1

Life-Threatening Differentials (Require Immediate Action)

Tickborne Rickettsial Diseases

• RMSF typically presents with fever, headache, and rash beginning on wrists/ankles/forearms as small blanching pink macules evolving to maculopapules 1
• Up to 40% of RMSF patients report no tick bite history, so absence of tick exposure should NOT exclude this diagnosis 1
• The rash appears 2-4 days after fever onset in most cases, but patients often seek care before rash develops 1
• 50% of RMSF deaths occur within 9 days of illness onset 1
• Peak season is April-September, but can occur year-round 1

Meningococcemia

• Cannot be reliably distinguished from tickborne diseases on clinical grounds alone 1
• Certain experts recommend administering intramuscular ceftriaxone pending blood cultures because of this diagnostic overlap 1

Common Infectious Differentials

Viral Exanthems

• Enteroviral infections can cause fever and rash in children, including palms and soles involvement 1
• Roseola (human herpesvirus 6) presents with rash after fever resolution 1
• Fifth disease (erythema infectiosum) shows "slapped cheek" appearance followed by lacy reticular rash 2

Eczema Herpeticum

• Multiple uniform "punched-out" erosions or vesiculopustular eruptions that are very similar in shape and size 3
• May progress rapidly to systemic infection without antiviral therapy 3
• Requires urgent recognition and systemic acyclovir 3

Secondary Bacterial Infection

• Look for crusts, discharge, or erosions suggesting superinfection 4
• Impetigo commonly affects face and extremities with honey-colored crusts 2

Non-Infectious Differentials

Atopic Dermatitis (Eczema)

• Pruritus is mandatory criterion 4
• Typically involves flexural areas in this age group 4
• Requires personal or family history of atopy plus dry skin and visible eczema 4
• 85% diagnosed by age 5 years 5

Contact Dermatitis

• History of new exposures to irritants or allergens 6
• Distribution corresponds to contact pattern 6

Drug Reactions

• Recent medication use is critical historical element 1

Immediate Diagnostic Approach

Critical History Elements

• Fever, headache, chills, myalgias, nausea/vomiting (suggests RMSF or ehrlichiosis) 1
• Recent outdoor activities, camping, hiking, or playing in brushy areas 1
• Tick exposure or pet exposure (pets can carry ticks) 1
• Geographic location and season 1
• Medication history 1
• Pruritus intensity and scratching behavior 4
• Family history of atopy 4

Physical Examination Priorities

• Check for rash on palms and soles (suggests RMSF, meningococcemia, or enterovirus) 1
• Assess for petechiae (indicates severe disease progression) 1
• Look for uniform "punched-out" lesions (eczema herpeticum) 3
• Examine scalp, axillae, groin for attached ticks 1
• Evaluate for conjunctival injection, altered mental status 1

Laboratory Testing

• CBC with differential (thrombocytopenia and bandemia suggest RMSF) 1
• Comprehensive metabolic panel 1
• Blood cultures 1
• Acute serum for IgG and IgM antibodies to R. rickettsii, E. chaffeensis, A. phagocytophilum (but DO NOT wait for results to treat) 1
• PCR for ehrlichiosis if available 1

Initial Management Algorithm

If ANY suspicion for RMSF or tickborne disease:

• Start doxycycline immediately without waiting for laboratory confirmation 1
• Consider intramuscular ceftriaxone to cover meningococcemia pending cultures 1
• Arrange close follow-up within 24-48 hours 1
• Obtain convalescent serology 2-4 weeks later for confirmation 1

If eczema herpeticum suspected:

• Start systemic acyclovir immediately 3
• Add empirical antibiotics (cephalexin or flucloxacillin) for secondary bacterial infection 3

If isolated contact dermatitis or atopic dermatitis without systemic symptoms:

• Topical corticosteroids for children ≥2 years (apply 3-4 times daily) 7
• Avoid triggers and irritants 4

Critical Pitfalls to Avoid

• Never exclude RMSF based on absence of tick bite history or geographic location 1
• Never wait for serologic confirmation before starting treatment for suspected RMSF—serology is negative in first week 1
• Never dismiss a rapidly evolving rash as "just eczema" without ruling out eczema herpeticum 3, 4
• Do not assume benign viral exanthem if systemic symptoms are present 1
• Recognize that rash may be absent in 20% of RMSF cases 1