What are the possible causes and treatments for a maculopapular rash confined to the upper chest?

Maculopapular Rash Confined to Upper Chest

For a maculopapular rash confined to the upper chest, the most critical first step is determining whether this represents a drug reaction, particularly if the patient is on anticancer therapy or recent antibiotics, as these are the most common causes requiring immediate intervention. 1, 2

Immediate Assessment

Key Clinical Features to Document

• Timing of onset relative to any new medications (particularly within 1-4 weeks of starting antibiotics, anticonvulsants, NSAIDs, or anticancer agents) 2, 3
• Presence of systemic symptoms including fever >38.5°C, mucosal involvement (oral ulcers, conjunctivitis, genital lesions), or skin detachment—any of these mandate immediate hospitalization 1, 2
• Extent of body surface area involvement: if >30% BSA, this is grade 3 and requires holding the offending agent 1
• Associated symptoms: pruritus, burning, or tenderness 1

Critical Red Flags Requiring Emergency Evaluation

• Fever with petechiae or purpura: consider meningococcemia or Rocky Mountain Spotted Fever, which can present initially on the trunk before spreading to extremities 1
• Mucosal involvement: suggests Stevens-Johnson syndrome or toxic epidermal necrolysis 3
• Rapid progression: particularly if developing within 3-5 days of symptom onset 1

Differential Diagnosis by Context

If Patient is on Anticancer Therapy (EGFR inhibitors, MEK inhibitors, mTOR inhibitors, or immune checkpoint inhibitors)

• Papulopustular eruption from EGFR inhibitors typically affects face and chest first 1
• Immune-related adverse events from checkpoint inhibitors can present as maculopapular rash 1, 2

If Recent Antibiotic Exposure

• Drug hypersensitivity reaction: most common with beta-lactams (amoxicillin-clavulanate, piperacillin-tazobactam), sulfonamides (cotrimoxazole), or aminoglycosides 3, 4, 5
• EBV-associated rash: if amoxicillin was given for presumed bacterial pharyngitis, consider underlying infectious mononucleosis 4

If Fever Present with Outdoor/Tick Exposure History

• Rocky Mountain Spotted Fever: begins as blanching pink macules on trunk/chest, evolving to maculopapular with central petechiae; up to 40% report no tick bite 1, 2
• Hemorrhagic fever: maculopapular rash prominent on trunk appears ~5 days after fever onset 1

Treatment Algorithm

Grade 1 (Rash <10% BSA, Minimal Symptoms)

• Continue current medications if not suspected as causative 1
• Topical corticosteroids: Class I (clobetasol propionate 0.05% or betamethasone dipropionate) for chest; apply twice daily 1
• Oral antihistamines: cetirizine 10 mg daily (non-sedating) or hydroxyzine 10-25 mg four times daily if sedation acceptable 1
• Emollients: fragrance-free, cream or ointment-based products twice daily 1

Grade 2 (Rash 10-30% BSA, Moderate Symptoms)

• Continue current medications unless drug reaction strongly suspected 1
• Escalate topical corticosteroids to higher potency if not already using Class I 1
• Add oral tetracycline antibiotics if on EGFR inhibitor: doxycycline 100 mg twice daily or minocycline 100 mg daily for at least 6 weeks 1
• Non-urgent dermatology referral 1
• Avoid skin irritants: no hot water washing, no over-the-counter anti-acne products, no harsh soaps 1

Grade 3 (Rash >30% BSA, Severe Symptoms or Limiting Self-Care)

• Hold suspected causative medication immediately 1
• Same-day dermatology consultation 1
• Systemic corticosteroids: prednisone 0.5-1 mg/kg/day (or equivalent methylprednisolone) until rash resolves to grade 1 or less, then taper over 4-6 weeks 1
• Rule out systemic involvement: obtain CBC with differential, comprehensive metabolic panel 1
• PCP prophylaxis: if immunosuppression expected >3 weeks (prednisone >30 mg/day equivalent) 1
• Proton pump inhibitor: for GI prophylaxis while on high-dose steroids 1

If Anticancer Therapy-Related (EGFR Inhibitor)

• Grade 1-2: initiate or escalate topical corticosteroids plus oral doxycycline 100 mg twice daily 1
• Grade 3: hold EGFR inhibitor until grade 1, add systemic corticosteroids (prednisone 0.5-1 mg/kg for 7 days with 4-6 week taper) 1
• If infection suspected (painful lesions, yellow crusts, pustules on arms/legs/trunk): obtain bacterial culture and treat based on sensitivities for at least 14 days 1

Diagnostic Workup

Essential Laboratory Tests

• If fever present: blood cultures, CBC with differential, comprehensive metabolic panel 1
• If drug reaction suspected: no specific tests required unless systemic involvement suspected 1
• If tick exposure or endemic area: acute and convalescent serology for Rickettsia rickettsii (2-4 weeks apart); note that serology is typically negative in first week 1

When to Perform Skin Biopsy

• Diagnosis unclear after history and examination 2, 3
• No response to 1-2 weeks of empiric treatment 3
• Severe reaction suspected requiring definitive diagnosis 2

Critical Pitfalls to Avoid

• Do not dismiss Rocky Mountain Spotted Fever based on absence of reported tick bite or non-endemic geography; 40% have no tick bite history and cases occur nationwide 1
• Do not delay empiric doxycycline if RMSF suspected based on clinical presentation; waiting for serologic confirmation increases mortality as 50% of deaths occur within 9 days 1
• Do not use topical vitamin K1 cream for EGFR inhibitor-related rash; randomized studies show no benefit 1
• Do not continue suspected causative drug if rash progresses to grade 3 or involves mucous membranes 1, 3
• Do not use over-the-counter anti-acne medications for anticancer therapy-related rash; these worsen barrier dysfunction 1