What is the treatment for an erythematous, pruritic rash in the axilla with a linear pattern?

Treatment of Linear Erythematous Pruritic Axillary Rash

Immediate Clinical Assessment

The most critical first step is to determine if this linear pattern represents Lyme disease (erythema migrans), which requires immediate antibiotic therapy, versus a drug-induced or inflammatory dermatosis that requires topical corticosteroids and antihistamines. 1

Key Diagnostic Features to Evaluate

• Timing and tick exposure: Erythema migrans typically appears 7-14 days (range 3-30 days) after tick bite and should be ≥5 cm in diameter 1
• Lesion characteristics: Erythema migrans in the axilla is a common location for Lyme disease and would show expanding erythema without significant scaling or vesiculation 1
• Medication history: Review all current medications, particularly immune checkpoint inhibitors, EGFR inhibitors, or other targeted cancer therapies that commonly cause pruritic rashes 1
• Infection signs: Rule out secondary bacterial infection (impetiginization from Staphylococcus aureus), herpes simplex, or dermatophyte infection 1

Treatment Algorithm

If Erythema Migrans (Lyme Disease) is Suspected

Treat immediately with oral antibiotics based on clinical diagnosis without waiting for serologic confirmation, as serology is too insensitive in the first 2 weeks of infection. 1

• Diagnosis is made by visual inspection in patients with compatible epidemiologic history 1
• The axilla is a typical location for erythema migrans 1
• Do not delay treatment for laboratory confirmation 1

If Drug-Induced or Inflammatory Dermatosis

Grade 1 (Mild): Rash <10% BSA

• Continue any causative medications and apply moderate-to-high potency topical corticosteroids 1
• Mometasone furoate 0.1% ointment or betamethasone valerate 0.1% ointment applied once to twice daily 1, 2
• Add loratadine 10 mg once daily as first-line oral antihistamine for daytime pruritus 1, 3
• For nighttime pruritus, use hydroxyzine 25-50 mg at bedtime or diphenhydramine 25-50 mg at bedtime 1, 3
• Apply topical emollients to restore skin barrier 1
• Avoid skin irritants including hot showers, excessive soaps, and alcohol-containing lotions 1

Grade 2 (Moderate): Rash 10-30% BSA or limiting instrumental activities

• Consider holding causative medication and monitor weekly 1
• Escalate to high-potency topical corticosteroid: clobetasol propionate 0.05% once daily for maximum 2 weeks 2
• Continue oral antihistamines as above 1, 3
• Consider oral prednisone 0.5-1 mg/kg daily, tapering over 4 weeks if topical therapy insufficient 1
• Topical menthol 0.5% can be added for additional antipruritic effect 1, 2
• Reassess after 2 weeks; if no improvement, escalate to Grade 3 management 1

Grade 3 (Severe): Rash >30% BSA with moderate-to-severe symptoms

• Hold causative medication immediately 1
• Initiate oral prednisone 1 mg/kg daily, tapering over at least 4 weeks 1
• Apply high-potency topical corticosteroids (clobetasol propionate 0.05%) 1, 2
• Add second-line therapy with pregabalin 25-150 mg daily or gabapentin 900-3600 mg daily if antihistamines fail 1, 2
• Consult dermatology to determine appropriateness of resuming causative medication 1

Specific Considerations for Axillary Location

• The axilla has thin, sensitive skin prone to corticosteroid-induced atrophy 2
• Limit clobetasol propionate use to 2-4 weeks maximum in the axilla, then reevaluate 2
• The axilla is a common site for contact dermatitis from deodorants, fragrances, and preservatives 1
• Eliminate potential contactants including fragranced products 1, 2

Critical Pitfalls to Avoid

• Do not dismiss a linear axillary rash as simple dermatitis without considering Lyme disease, especially with appropriate epidemiologic exposure 1
• Do not use high-potency corticosteroids continuously beyond 4 weeks without dermatology supervision due to skin atrophy risk 2
• Do not ignore secondary bacterial infection (impetiginization), which requires bacterial swabs and calculated antibiotic therapy 1
• Do not use sedating antihistamines in elderly patients due to fall risk 2
• Avoid calamine or crotamiton, which are ineffective 2

Reassessment Timeline

• At 2 weeks: If insufficient improvement with topical corticosteroids, add oral antihistamines if not already prescribed 1
• At 4 weeks: If pruritus persists despite corticosteroids and antihistamines, add GABA agonists (pregabalin or gabapentin) 1, 2
• Refer to dermatology if no response after 4-6 weeks of optimal treatment 2