What is the diagnosis and treatment for a patient presenting with a rash on the trunk and face?

Rash on Trunk and Face: Diagnostic Approach and Management

Immediate Assessment Priority

The first critical step is to determine if this is a life-threatening condition requiring immediate intervention by assessing for fever, systemic toxicity, and rash morphology. 1, 2

Red Flag Assessment

• Check for fever and systemic signs including tachycardia, hypotension, altered mental status, or respiratory distress, as these indicate potentially fatal conditions like meningococcemia or Rocky Mountain Spotted Fever (RMSF) 2
• Examine rash morphology carefully: petechial/purpuric rashes with fever demand immediate empiric antibiotics, as 50% of RMSF deaths occur within 9 days and delay significantly increases mortality 2
• Document temperature pattern: spiking fevers ≥39°C for ≥7 days suggest Still's disease, while continuous high fever with rash suggests infectious etiologies 1

Primary Differential Diagnoses by Clinical Pattern

If Fever Present with Maculopapular Rash on Trunk and Face:

Still's Disease (Adult-Onset or Systemic Juvenile Idiopathic Arthritis):

• Salmon-pink, erythematous, transient rash that coincides with fever spikes, preferentially involving trunk 1
• Fever ≥39°C for at least 7 days is the hallmark presentation 1
• Requires CBC with differential looking for neutrophilic leukocytosis, and inflammatory markers (CRP, ESR, ferritin) 1
• Critical complication: Monitor for macrophage activation syndrome (MAS) with persistent fever, splenomegaly, rising ferritin, falling cell counts, and abnormal liver function 1

Kawasaki Disease (if pediatric patient):

• Fever persisting at least 5 days with polymorphous nonspecific diffuse maculopapular eruption appearing within 5 days of fever onset 1
• Key distinguishing feature: bilateral bulbar conjunctival injection without exudate 1
• Requires urgent echocardiography to monitor for coronary artery involvement 1

Measles:

• Maculopapular rash that begins on face and spreads cephalocaudally to trunk and extremities 3
• Preceded by 2-4 day prodrome of fever, cough, coryza, and conjunctivitis

If Rash WITHOUT Facial Involvement:

Acute Rheumatic Fever:

• Erythema marginatum is unique, evanescent, pink rash with pale centers and rounded or serpiginous margins 3
• Specifically spares the face - rash is present on trunk and proximal extremities only 3
• Heat can induce its appearance, and it blanches with pressure 3

If Drug Exposure History Present:

EGFR Inhibitor-Induced Acneiform Rash (if on cancer therapy):

• Macular, papular, or pustular lesions in regions rich in sebaceous glands like face and upper trunk, developing within 2-4 weeks of treatment 3
• Different from acne vulgaris as there are no comedones 3
• Manage with topical glucocorticoids for mild cases; severe cases require TKI dose reduction or temporary discontinuation 3

DRESS Syndrome:

• Maculopapular rash on trunk and face that can extend to involve >50% body surface area 4
• Associated with eosinophilia, hepatosplenomegaly, and acute kidney/liver injury 4
• Mortality rate up to 10% - requires immediate discontinuation of culprit drug and systemic glucocorticoids 4
• Common culprits include amoxicillin-clavulanate, vancomycin, and other antibiotics 4

Essential Diagnostic Workup

Laboratory studies to order immediately:

• Complete blood count with differential to assess for neutrophilic leukocytosis (Still's disease), eosinophilia (DRESS), or thrombocytopenia (infectious causes) 1, 2
• Inflammatory markers: CRP, ESR, and ferritin (markedly elevated ferritin suggests Still's disease) 1
• Comprehensive metabolic panel to assess for hepatic/renal involvement 2
• Blood cultures before antibiotics if infectious etiology suspected 2

When to perform skin biopsy:

• If diagnosis remains unclear after initial evaluation and rash persists despite empiric treatment 5
• When unique variants of common conditions are suspected (e.g., patch granuloma annulare mimicking cutaneous lymphoma) 5
• To confirm DRESS syndrome (shows interface dermatitis with eosinophilic infiltrates) 4

Treatment Algorithm

If Systemic Toxicity or Petechial/Purpuric Component Present:

Start empiric doxycycline immediately if RMSF cannot be excluded, even in children <8 years old 2

• Add ceftriaxone if meningococcemia cannot be excluded based on clinical presentation 2
• Hospitalize for systemic toxicity, rapidly progressive rash, or diagnostic uncertainty 2

If Drug-Induced Rash Suspected:

Discontinue all potential culprit medications immediately 4

• For DRESS syndrome: initiate systemic glucocorticoids (prednisone 1 mg/kg daily) 3, 4
• For EGFR inhibitor rash: topical glucocorticoids or antihistamines for mild cases; dose reduction or temporary discontinuation for severe cases 3

If Still's Disease Suspected:

Initiate NSAIDs and monitor closely for MAS 1

• Consider systemic glucocorticoids if inadequate response
• Monitor ferritin, cell counts, and liver function serially 1

Critical Pitfalls to Avoid

• Do not wait for the classic triad of fever, rash, and specific exposure history in RMSF, as it is present in only a minority of patients at initial presentation 2
• Do not exclude serious disease based on absence of certain features: up to 20% of RMSF cases lack rash entirely 2
• Do not delay treatment for laboratory confirmation in suspected life-threatening conditions like RMSF or meningococcemia 2
• Do not dismiss widespread rash as benign without considering DRESS syndrome if patient has recent antibiotic exposure, as mortality can reach 10% 4
• Do not treat empirically without biopsy if rash persists or worsens despite initial therapy, as unique variants may require histologic diagnosis 5