What is the diagnosis and treatment for a patient presenting with a widespread rash, itchiness, and red spots across their body, including arms, back, torso, and legs?

Widespread Pruritic Rash: Diagnosis and Management

Immediate Priority: Rule Out Life-Threatening Conditions First

The most critical first step is to immediately assess for Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), or Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), as these are life-threatening emergencies requiring immediate hospitalization. 1

Emergency Red Flags Requiring Immediate Action

• Skin sloughing or epidermal detachment – If any areas show skin peeling away with minimal trauma, suspect SJS/TEN and discontinue ALL medications immediately 2, 1
• Mucosal involvement – Check for erosions or blistering in the mouth, eyes, nose, or genitalia, which strongly suggests SJS/TEN 2
• Purpuric macules or flat atypical targets – Dark red flat lesions with dusky centers indicate potential SJS/TEN 2
• Body surface area >30% with erythema – This represents Grade 4 toxicity requiring emergency hospitalization 1

If Emergency Features Present

Immediately discontinue all suspected medications and initiate IV methylprednisolone 1-2 mg/kg with emergency hospitalization and dermatology consultation. 1 Do not wait for biopsy results to begin treatment if clinical suspicion is high 1.

Step 2: Assess for Infectious Causes with Systemic Toxicity

Rocky Mountain Spotted Fever (RMSF) and Meningococcemia

If the patient has fever, headache, and systemic symptoms alongside the rash, consider RMSF or meningococcemia 3:

• RMSF characteristics: Rash typically begins on ankles, wrists, or forearms as small blanching pink macules evolving to maculopapular lesions, appearing 2-4 days after fever onset 2, 3
• Critical pitfall: Up to 20% of RMSF cases lack rash entirely, and only 60% report tick exposure 3
• Palms and soles involvement: When present, indicates advanced disease requiring immediate treatment 3
• Timing matters: 50% of RMSF deaths occur within 9 days of illness onset 3

If RMSF cannot be excluded based on clinical presentation, start empiric doxycycline immediately without waiting for laboratory confirmation or the classic triad of symptoms. 3 Add ceftriaxone if meningococcemia cannot be ruled out 3.

Key Distinguishing Features

• Petechial progression: If red spots evolve to non-blanching petechiae or purpura, this suggests RMSF, meningococcemia, or other serious bacterial infections 2, 3
• Rapid progression: Meningococcemia progresses more rapidly than RMSF 3
• Seasonal timing: RMSF peaks April-September 3

Step 3: Evaluate for Drug-Induced Eruptions

Medication History is Essential

• Review ALL medications started within the past 6 weeks, including over-the-counter drugs and supplements 1, 4
• SJS/TEN typically occurs after week 6 of treatment with certain high-risk medications (protease inhibitors, immune checkpoint inhibitors, EGFR inhibitors) 1
• Drug-induced eruptions account for up to 15% of facial rashes and can be widespread 4

Grading Severity Using Body Surface Area

• Grade 1: <10% BSA – Topical management appropriate 4
• Grade 2: 10-30% BSA – Withhold causative agent, consider systemic treatment 1, 4
• Grade 3: >30% BSA or Grade 2 with substantial symptoms – Requires systemic corticosteroids 1, 4
• Grade 4: Skin sloughing >30% BSA with erythema, purpura, or epidermal detachment – Emergency hospitalization required 1, 4

Step 4: Consider Common Benign Causes

If No Emergency Features Present

For widespread pruritic rash without skin sloughing, mucosal involvement, or systemic toxicity, consider 5, 6:

• Viral exanthems – Often self-limited, may have prodromal symptoms 5
• Contact dermatitis – Assess for new exposures to allergens or irritants 5
• Urticaria – Raised, blanching wheals that migrate over hours 6
• Eczematous eruptions – Dry, scaly patches with excoriations from scratching 7

Initial Management for Non-Emergency Cases

For mild to moderate pruritic rash without concerning features, topical hydrocortisone applied to affected areas 3-4 times daily is appropriate initial treatment. 8 However, this should only be used after ruling out serious causes 8.

Step 5: Diagnostic Testing Strategy

When to Obtain Laboratory Studies

• CBC with differential: Look for thrombocytopenia (suggests RMSF), eosinophilia (suggests DRESS), or leukopenia 3
• Comprehensive metabolic panel: Assess for hyponatremia or hepatic transaminase elevations 3
• Blood cultures: If systemic toxicity present, obtain before antibiotics but do not delay treatment 3

When to Perform Skin Biopsy

Obtain punch biopsy for Grade 2 or higher rashes not responding to initial treatment, atypical presentations, or when diagnosis remains unclear after initial evaluation. 4 Histopathology is necessary to support clinical assessment of SJS/TEN and exclude other blistering dermatoses 2.

Critical Pitfalls to Avoid

• Do not wait for the classic triad of fever, rash, and tick bite in RMSF – it is present in only a minority at initial presentation 3
• Do not exclude serious disease based on absence of certain features – up to 20% of RMSF cases lack rash, and rash may be completely absent or atypical in SJS/TEN 2, 3
• Do not delay treatment waiting for laboratory confirmation when clinical suspicion for life-threatening conditions is high 1, 3
• Do not apply topical antibiotics prophylactically – reserve only for documented superinfection 1
• Do not dismiss prodromal symptoms – visible skin changes may lag behind systemic symptoms by 24-72 hours 4

When to Obtain Immediate Specialist Consultation

Immediate dermatology consultation is required for: 1, 4

• Any Grade 3 or 4 rash
• Suspected SJS, TEN, or DRESS
• Skin sloughing exceeding 30% BSA
• Presence of mucosal involvement with systemic symptoms
• Rapidly progressive rash with diagnostic uncertainty

Emergency admission to burn unit or intensive care is required for Grade 4 skin necrosis/sloughing. 1