What are the red flags for rash in adults?

Red Flags for Rash in Adults

When evaluating an adult with a rash, immediately assess for life-threatening conditions by looking for the RAPID criteria: Redness (especially bilateral), Acuity loss (vision), Pain (ocular or severe), Intolerance to light, and Damage to cornea—any of these warrant emergency ophthalmology referral within 24 hours. 1

Critical Red Flags Requiring Immediate Action

Systemic Illness Indicators

• Fever with petechial or purpuric rash that does not blanch, particularly if rapidly progressive—suggests meningococcemia, Rocky Mountain spotted fever, or other life-threatening infections requiring immediate treatment 1, 2
• High spiking fever (>39°C) with rash, especially if accompanied by hypotension, altered mental status, or multi-organ dysfunction 1, 3
• Mucosal involvement (eyes, mouth, nose, genitalia) with painful skin lesions—highly suggestive of Stevens-Johnson syndrome/toxic epidermal necrolysis 1

Dermatologic Emergency Signs

• Epidermal detachment or skin sloughing (positive Nikolsky sign)—indicates Stevens-Johnson syndrome/TEN with mortality risk of 5-10% if untreated 1
• Rapidly progressive purpuric lesions evolving to necrosis or gangrene within hours to days 1
• Vesiculobullous eruptions with systemic toxicity, particularly if accompanied by respiratory distress or hemodynamic instability 1, 4

Specific High-Risk Patterns

• Rash involving palms and soles with fever—consider Rocky Mountain spotted fever (5-10% mortality), meningococcemia, or other rickettsial diseases 1
• Petechial rash appearing on day 5-6 of illness after initial maculopapular presentation—indicates progression of RMSF to severe disease 1
• Cutaneous necrosis with thrombocytopenia and renal failure—may mimic thrombotic thrombocytopenic purpura but could represent severe RMSF 1

Respiratory and Neurologic Warning Signs

Respiratory Compromise

• Cough, dyspnea, bronchial hypersecretion, or hemoptysis accompanying rash—suggests respiratory tract involvement requiring urgent evaluation 1
• Oxygen saturation decline on pulse oximetry in a patient with rash and fever 1

Neurologic Deterioration

• Altered mental status, confusion, or decreased level of consciousness with rash—consider encephalitis, meningococcemia, or severe rickettsial disease 1
• Severe headache with photophobia and rash, particularly if accompanied by neck stiffness 1
• Seizures, focal neurologic deficits, or acute transient hearing loss in the context of fever and rash 1
• Abdominal pain severe enough to mimic acute appendicitis with fever and rash—can occur in RMSF or ehrlichiosis 1

Cardiovascular and End-Organ Dysfunction

• Hypotension or shock with rash—suggests toxic shock syndrome, meningococcemia, or severe sepsis 1, 3
• Arrhythmias detected on examination or monitoring in patients with systemic rash 1
• Periorbital or peripheral edema (especially in children) with fever and rash—may indicate severe systemic involvement 1
• Oliguria or anuria suggesting acute renal failure 1

Ocular Red Flags (RAPID Criteria Detail)

• Unilateral redness should prompt consideration of herpes simplex virus or other focal infection requiring emergency evaluation 1
• Moderate to severe ocular pain (beyond irritation) of new onset 1
• Visual acuity loss of any degree 1
• Corneal damage visible as uptake of fluorescein, ulceration, haze, opacity, or purulent discharge 1
• Photophobia with conjunctival injection 1

Timing and Progression Concerns

• Rash appearing before day 3 of fever or absence of rash by day 5-6 in suspected rickettsial disease—both patterns associated with delayed diagnosis and increased mortality 1
• Rapid progression of lesions from macules to papules to vesicles to necrosis within 24-48 hours 1, 4
• Symptoms developing within 2 months of new medication exposure, particularly antibiotics, anticonvulsants, or allopurinol—suggests drug reaction with potential for SJS/TEN 1

Laboratory and Clinical Context Red Flags

• Thrombocytopenia with fever and rash—seen in rickettsial diseases, ehrlichiosis, meningococcemia, and drug reactions 1, 3
• Leukopenia or leukocytosis with left shift accompanying rash and fever 1
• Elevated liver transaminases (>3x normal) with systemic rash 1
• Hyponatremia in the context of fever and rash—common in RMSF and ehrlichiosis 1

Common Pitfalls to Avoid

• Do not wait for the "classic" presentation—up to 20% of RMSF cases never develop a rash, and lack of rash is associated with increased mortality 1
• Do not dismiss rash in darker-skinned patients—petechiae and erythema may be difficult to visualize but are still present 1
• Do not assume labial herpes indicates HSV encephalitis—it is merely a marker of critical illness without diagnostic specificity 1
• Do not delay treatment pending confirmatory testing when clinical suspicion for life-threatening infection is high—empiric therapy for RMSF or meningococcemia should begin immediately 1

Immediate Actions When Red Flags Present

• Discontinue all potential culprit medications immediately 1
• Establish IV access and begin fluid resuscitation if hemodynamically unstable 1
• Obtain blood cultures, complete blood count, comprehensive metabolic panel, and coagulation studies before initiating antibiotics 1
• Initiate empiric doxycycline (100 mg twice daily) if rickettsial disease suspected, regardless of age 1
• Arrange emergency dermatology or ophthalmology consultation for suspected SJS/TEN or ocular involvement 1
• Consider ICU admission for patients with epidermal detachment >10% body surface area, respiratory compromise, or hemodynamic instability 1