What is the best treatment for a 2 mm erythemic raised lesion on the upper arm?

Treatment of a 2 mm Erythemic Raised Lesion on the Upper Arm

For a 2 mm erythemic raised lesion on the upper arm, topical hydrocortisone 1% cream applied twice daily for 2-4 weeks is the recommended first-line treatment.

Diagnostic Considerations

Before initiating treatment, it's important to consider the differential diagnosis for a small erythemic raised lesion:

1. Inflammatory dermatoses:

   • Contact dermatitis
   • Insect bite reaction
   • Small eczematous patch
   • Early erythema nodosum

2. Infectious causes:

   • Early erythema migrans (Lyme disease) - though typically these become >5 cm 1
   • Folliculitis

3. Neoplastic lesions:

   • Early Bowen's disease (squamous cell carcinoma in situ)
   • Small hemangioma

Treatment Algorithm

First-line Treatment:

• Topical hydrocortisone 1% cream applied twice daily for 2-4 weeks 2, 3, 4
  • Low-potency steroid appropriate for small, mildly inflammatory lesions
  • Available over-the-counter
  • Minimal risk of skin atrophy with short-term use
  • Effective for reducing erythema, inflammation, and associated pruritus

Monitoring:

• Mark the borders of the lesion to monitor for expansion 1
• If the lesion expands beyond 5 cm, consider Lyme disease evaluation
• Reassess after 2 weeks of treatment

If No Improvement After 2 Weeks:

1. Consider topical antibiotic therapy:

   • Erythromycin 1.5% solution twice daily if bacterial folliculitis is suspected 3
   • Can be combined with hydrocortisone in a controlled regimen

2. Consider stronger topical steroid:

   • Triamcinolone 0.1% cream for more resistant inflammatory lesions 5
   • Apply twice daily for 2 weeks

Special Considerations:

• If lesion is scaling or has vesicles/pustules: Consider antifungal cream (clotrimazole 1%) in addition to hydrocortisone 1

• If lesion is associated with systemic symptoms (fever, malaise):

  • Obtain bacterial culture if pustular
  • Consider systemic antibiotics if infection suspected 1

Important Caveats

1. Duration of treatment: Limit topical steroid use to 2-4 weeks to prevent skin atrophy, especially on thin skin areas

2. Red flags requiring dermatology referral:

   • Rapid growth
   • Ulceration
   • Bleeding
   • Irregular borders
   • Failure to respond to treatment after 4 weeks

3. Avoid high-potency steroids on the face, groin, or axillary regions due to increased risk of skin atrophy

4. Patient education: Advise to avoid scratching, keep the area clean, and report any changes in appearance or symptoms

The small size (2 mm) and erythemic raised nature of the lesion suggests a benign inflammatory process that should respond well to topical hydrocortisone. If the lesion persists or changes in appearance despite appropriate treatment, a skin biopsy may be warranted to rule out neoplastic processes.