What is the management for a skin lesion papule under the arm?

Management of Papular Skin Lesions in the Underarm

For a papular skin lesion in the underarm, perform an excisional biopsy with a 2mm margin of normal skin to establish a definitive diagnosis, as management depends entirely on the underlying etiology—ranging from benign self-limited conditions to life-threatening infections or malignancies. 1

Initial Diagnostic Approach

Critical Clinical Assessment

The first priority is determining whether the patient is immunocompromised, as this fundamentally changes the differential diagnosis and urgency of management 1:

• Immunocompromised patients (neutropenia, HIV/AIDS, organ transplant recipients, those on anti-TNF therapy or other immunosuppressants) require immediate dermatology consultation familiar with cutaneous manifestations of infection in cellular immune defects 1
• Document fever, systemic symptoms, rapidity of lesion development, and presence of pain or tenderness 1
• Examine for multiple lesions, distribution pattern (dermatomal vs. scattered), and associated findings (lymphadenopathy, erythema, necrosis) 1

Biopsy Technique and Timing

Perform excisional biopsy rather than incisional biopsy whenever feasible 1:

• Use a 2mm margin of normal skin with elliptical incision parallel to skin tension lines 1
• Avoid tissue destruction methods (laser, electrocautery) that compromise histologic assessment 1
• In immunocompromised patients with suspected infection, consider early biopsy and surgical debridement (within 24-48 hours) as both diagnostic and potentially therapeutic 1
• Never use frozen sections for suspected melanocytic lesions 1

Send tissue for:

• Routine histopathology (standard) 1
• Bacterial, fungal, and mycobacterial cultures if infection suspected 1
• Special stains (Gram, PAS, GMS, acid-fast) if infectious etiology considered 1

Management Based on Clinical Context

Immunocompromised Patients with Fever

This represents a medical emergency requiring immediate empiric therapy 1:

• Blood cultures before antibiotics (positive in 40-50% of disseminated fungal infections like Fusarium) 1
• Empiric broad-spectrum antibiotics covering gram-negative organisms (antipseudomonal beta-lactam such as piperacillin-tazobactam) 1
• Add empiric antifungal coverage (liposomal amphotericin B) if fever persists beyond 4-7 days or if lesions show central necrosis, as fungal infections (Candida, Aspergillus, Fusarium, Mucor) commonly present as erythematous papules progressing to necrotic nodules 1
• Consider empiric acyclovir if vesicular component suggests HSV or VZV 1, 2, 3

Common pitfall: Ecthyma gangrenosum classically associated with Pseudomonas can be mimicked by multiple other organisms including fungi and HSV, so broad empiric coverage is essential 1

Immunocompetent Patients

Benign Self-Limited Conditions

If clinical features suggest granuloma annulare (flesh-colored to erythematous grouped papules, typically on extremities) 4, 5:

• Reassurance alone is appropriate for localized disease, as it resolves spontaneously within 1-2 years 4
• Treatment options if cosmetically concerning: liquid nitrogen, intralesional corticosteroids, or topical steroids under occlusion 4
• Biopsy confirms diagnosis but is not mandatory if classic presentation 4

Infectious Etiologies

Fungal (Tinea corporis): If annular, pruritic, erythematous patch with scale 5:

• Potassium hydroxide examination of scrapings establishes diagnosis 5
• Topical antifungals for localized disease 5

Nontuberculous mycobacteria: If poorly resolving nodules or subcutaneous abscesses 1:

• Requires prolonged combination therapy (6-12 weeks) with macrolide (clarithromycin) plus second agent based on susceptibilities 1
• Surgical debridement crucial for culture and removal of devitalized tissue 1

Nocardia: If subcutaneous nodules in patient with pulmonary symptoms 1:

• Represents metastatic foci from primary pulmonary source 1
• Requires systemic antimicrobial therapy based on species identification 1

Malignant Considerations

Melanoma: If papule shows asymmetry, irregular borders, color heterogeneity, diameter >6mm, or recent evolution 1:

• Complete excision with 2mm margin is mandatory (not incisional biopsy) 1
• Histopathology must include Breslow thickness, Clark level, and margin assessment 1
• Re-excision with wider margins required if melanoma confirmed 1

Cutaneous lymphoma: If persistent papules, especially if multiple or associated with systemic symptoms 1:

• Lymphomatoid papulosis presents as recurrent self-healing papulonecrotic lesions 1
• Expectant policy appropriate for LyP with few lesions; low-dose methotrexate (5-20mg weekly) for cosmetically disturbing disease 1
• Primary cutaneous CD30+ anaplastic large cell lymphoma requires radiotherapy (24-30 Gy) or excision for solitary lesions 1

Special Situations

Vesicular Component Present

Consider herpes zoster if dermatomal distribution 2, 3:

• Initiate valacyclovir 1g PO three times daily within 72 hours of rash onset 2
• Continue until all lesions scabbed (may exceed 7 days) 2
• Critical pitfall: HSV can mimic zoster morphologically but lacks dermatomal distribution; laboratory confirmation (PCR) essential if uncertain 3

Drug-Related Papular Eruptions

If patient on EGFR inhibitors, MEK inhibitors, or mTOR inhibitors 1:

• Grade 1-2: Continue drug, add oral doxycycline 100mg twice daily for 6 weeks plus topical moderate-potency steroid 1
• Grade ≥3: Interrupt drug until grade ≤1, add systemic corticosteroids (prednisone 0.5-1 mg/kg for 7 days with taper) 1
• Obtain bacterial cultures if infection suspected (painful lesions, yellow crusts, discharge) 1

Key Pitfalls to Avoid

• Never delay biopsy in immunocompromised patients with unexplained papular lesions, as mortality from disseminated fungal or bacterial infections remains high despite treatment 1
• Do not assume benign etiology based on appearance alone—multiple serious conditions (disseminated candidiasis, fusarium, aspergillus) present initially as innocuous-appearing papules 1
• Avoid topical therapy alone for suspected viral infections; systemic antivirals are required 2
• Do not use scalpel biopsy techniques that destroy tissue (cautery, laser) as this compromises diagnostic accuracy 1
• In patients with cellular immune defects, empiric broad-spectrum antimicrobials (antibacterial, antifungal, antiviral) should be initiated in life-threatening situations before culture results, with input from dermatology and infectious disease 1