What is the appropriate evaluation and treatment approach for a patient presenting with a purple bumpy rash, considering their age, medical history, and potential exposures?

Purple Bumpy Rash: Evaluation and Management

A purple bumpy rash requires immediate assessment for life-threatening conditions, particularly meningococcemia, Rocky Mountain spotted fever, and vasculitis—the presence of fever, systemic symptoms, or non-blanching purpura mandates urgent evaluation and empiric treatment before diagnostic confirmation.

Immediate Red Flags Requiring Emergency Action

• Non-blanching purpura with fever and systemic illness suggests meningococcemia or other bacterial sepsis—obtain blood cultures and initiate empiric antibiotics immediately 1, 2
• Petechial rash progressing to purpura in a febrile patient, especially with headache and altered mental status, requires immediate lumbar puncture after blood cultures 2
• Palpable purpura (raised, purple bumps) indicates vasculitis, which can be life-threatening if associated with systemic involvement 1, 3

Critical History Elements

• Tick exposure or outdoor activities in endemic areas within the past 2 weeks—Rocky Mountain spotted fever presents with fever, headache, and rash that begins as pink macules on wrists/ankles, progressing to petechial/purpuric bumps by day 5-6 1
• Medication history within the past 3 weeks—drug-induced vasculitis or DRESS syndrome can present with purpuric rash and systemic symptoms 1
• Recent viral illness in children—Henoch-Schönlein purpura (IgA vasculitis) typically follows upper respiratory infection and presents with palpable purpura on lower extremities and buttocks 3
• Immunotherapy exposure—checkpoint inhibitors can cause vasculitis with purpuric rash 1

Physical Examination Priorities

• Assess blanching—press firmly on the rash; non-blanching purple lesions indicate extravasated blood (purpura) and suggest vasculitis or thrombocytopenia 1, 2
• Palpate the lesions—raised, palpable purpura strongly suggests vasculitis rather than simple thrombocytopenia 3
• Distribution pattern—RMSF classically involves palms and soles by day 5-6; HSP affects lower extremities and buttocks; drug reactions are often generalized 1, 3
• Look for eschars—a necrotic lesion at tick bite site suggests rickettsial disease other than RMSF 1
• Check for mucosal involvement—oral lesions, conjunctival injection, or genital ulcers suggest Stevens-Johnson syndrome or other severe drug reactions 1

Essential Immediate Laboratory Testing

• Complete blood count with differential—thrombocytopenia suggests RMSF, meningococcemia, or IgA vasculitis; leukopenia with increased immature neutrophils suggests RMSF 1, 4
• Comprehensive metabolic panel—hyponatremia is common in RMSF; elevated creatinine suggests renal involvement in vasculitis 1, 3
• Coagulation studies—PT/PTT/INR to evaluate for disseminated intravascular coagulation 2
• Blood cultures before antibiotics if fever present 2
• Urinalysis—hematuria and proteinuria indicate renal involvement in vasculitis 3

Algorithmic Approach to Management

If Fever + Non-Blanching Purple Rash + Systemic Illness:

1. Obtain blood cultures immediately 2
2. Initiate empiric doxycycline 100 mg IV/PO twice daily for presumed RMSF if tick exposure or endemic area—do not wait for rash to involve palms/soles, as this indicates advanced disease with higher mortality 1
3. Add vancomycin 15-20 mg/kg IV plus ceftriaxone 2g IV if meningococcemia cannot be excluded 2
4. Perform lumbar puncture after blood cultures if altered mental status or meningeal signs present 2

If Palpable Purpura Without Fever (Vasculitis):

1. Obtain skin biopsy for histopathology and direct immunofluorescence to confirm vasculitis and determine type 3
2. Screen for systemic involvement—urinalysis, comprehensive metabolic panel, chest X-ray 3
3. Consider HSP in children—typically self-limited but requires monitoring for renal complications; check urinalysis weekly for 6 months 3
4. Evaluate for drug-induced vasculitis—discontinue suspected medications if clinically safe 1

If Purple Rash in Patient on Immunotherapy:

1. Assess body surface area involvement using the "rule of nines" 1
2. Grade 1-2 (<30% BSA)—continue immunotherapy with topical steroids and close monitoring 1
3. Grade 3 (>30% BSA or Grade 2 with substantial symptoms)—withhold immunotherapy, initiate systemic corticosteroids 0.5-1 mg/kg prednisolone, obtain dermatology consultation and skin biopsy 1
4. Grade 4 (skin sloughing >30% BSA)—permanently discontinue immunotherapy, hospitalize, initiate IV methylprednisolone 1-2 mg/kg, urgent dermatology consultation 1

Common Pitfalls to Avoid

• Do not wait for the classic triad of fever, rash, and tick bite in RMSF—this occurs in only a minority of patients at initial presentation, and delayed treatment increases mortality from 5-10% to much higher rates 1
• Do not wait for palms and soles involvement in RMSF—this is a late finding (day 5-6) indicating advanced disease; treat empirically if clinical suspicion exists 1
• Do not assume absence of rash rules out RMSF—less than 50% have rash in first 3 days, and some never develop rash 1
• Do not use sedating antihistamines for symptomatic relief, especially in elderly patients—increased fall risk and potential dementia association 1, 5
• Do not delay antibiotics for diagnostic testing in suspected bacterial sepsis with purpuric rash—mortality increases dramatically with each hour of delay 2

When to Consult Specialists

• Immediate infectious disease consultation if RMSF or meningococcemia suspected 1, 2
• Urgent dermatology consultation for skin biopsy if vasculitis suspected or if immunotherapy-related Grade 3-4 toxicity 1, 3
• Nephrology consultation if urinalysis shows significant hematuria or proteinuria in vasculitis 3