What is the most likely diagnosis for a patient with a recurrent rash exclusively along old scar areas?

Recurrent Rash Exclusively Along Old Scar Areas

The most likely diagnosis for a recurrent rash that appears exclusively along old scar areas is keloid or hypertrophic scar with recurrent inflammation, representing chronic inflammatory flares within the reticular dermis rather than a new dermatologic condition.

Understanding the Pathophysiology

Keloids and hypertrophic scars are not simply healed wounds but rather represent chronic inflammatory disorders of the reticular dermis that can persist and flare for years or decades after the initial injury 1. The key distinguishing feature is that these lesions result from aberrant wound healing characterized by:

• Continuous localized inflammation in the reticular dermis with inflammatory cells, increased fibroblasts, newly formed blood vessels, and excessive collagen deposits 1
• Upregulation of proinflammatory factors including IL-1α, IL-1β, IL-6, and tumor necrosis factor-α, making the tissue hypersensitive to trauma and prone to recurrent inflammatory episodes 1
• Progressive nature that can enlarge over decades, unlike normal scars 2

The recurrent "rash" pattern along old scars reflects episodic inflammatory flares triggered by various stimuli (mechanical stress, infection, systemic factors) rather than a separate skin condition 1.

Clinical Differentiation: Keloid vs. Hypertrophic Scar

While both represent the same underlying inflammatory process, the clinical differences reflect variations in inflammation intensity and duration 1:

Hypertrophic Scars

• Remain confined to the original injury site 2
• Typically regress spontaneously within 12-24 months 2
• Less likely to have severe recurrent inflammatory episodes

Keloids

• Extend beyond the original injury boundaries and can grow considerably in volume and surface area 2
• Progress over decades without spontaneous regression 2
• More prone to recurrent inflammatory flares with associated symptoms 2
• When multiple keloids develop in a single patient, this is termed "keloid disease" with autosomal dominant inheritance 2

Key Clinical Features to Assess

When evaluating recurrent inflammation along old scars, document:

• Location and extent: Does the inflammation remain within the original scar boundaries (hypertrophic) or extend beyond them (keloid)? 2
• Associated symptoms: Intense neurogenic pruritus, pain, and recurrent suppuration are characteristic of keloid disease 2
• Patient demographics: Keloid disease preferentially affects people of non-European ancestry, especially those of sub-Saharan African descent 2
• Family history: Autosomal dominant pattern suggests keloid disease 2
• Timing: Superficial injuries that don't reach the reticular dermis never cause these pathological scars 1

Important Differential Considerations

Hidradenitis Suppurativa

While HS can cause recurrent inflammation and scarring, it presents with painful nodules and abscesses in body folds (axillae, inguinal, anogenital regions) that rupture and form sinus tracts 3. The pattern is distinctly different from inflammation confined to pre-existing surgical or traumatic scars.

Local Scar Recurrence of Melanoma

This represents a completely different entity requiring pathologic confirmation by biopsy and staging imaging 3, 4. True melanoma recurrence would show progressive growth rather than episodic inflammatory flares 3.

Management Approach

The treatment strategy should focus on reducing inflammation in the reticular dermis 1, 5:

First-Line Interventions

• Intralesional corticosteroid injections to decrease connective tissue components and reduce inflammation 5, 6
• Topical corticosteroid ointments or tapes for inflammatory reduction 5
• Silicone gel sheets for occlusion and tension reduction 5, 6

Second-Line Options for Refractory Cases

• OnabotulinumtoxinA injections appear superior to both fluorouracil and corticosteroids for treating keloids and hypertrophic scars 5
• Intralesional cryotherapy with liquid nitrogen is beneficial, especially when combined with corticosteroids 5, 6
• Pulsed-dye laser therapy for symptomatic improvement and erythema reduction 6

Advanced Interventions

• Surgical revision with tension-reducing techniques combined with postoperative steroid injection (administered 10-14 days post-surgery), laser ablation, or radiation therapy 5
• Radiation therapy can be used alone or in combination, with low cancer risk 5

Critical Pitfall to Avoid

Do not perform simple surgical excision alone, as this results in 45-100% recurrence rates 6. Excision must always be combined with adjunctive therapies such as postoperative corticosteroid injections, radiation, or laser treatment to prevent recurrence 5, 6.