Can Disney rash (also known as groove sign) occur unilaterally, affecting only one leg?

Disney Rash (Exercise-Induced Vasculitis) Can Present Unilaterally

Yes, Disney rash (exercise-induced vasculitis) can occur unilaterally, affecting only one leg, although bilateral presentation is more common. While the literature doesn't specifically address unilateral presentation of Disney rash, the pathophysiology of exercise-induced vasculitis supports the possibility of unilateral manifestation based on differential exposure and vascular compromise.

Understanding Disney Rash (Exercise-Induced Vasculitis)

Disney rash, also known as exercise-induced vasculitis or "golfer's vasculitis," is characterized by:

• Erythematous, pruritic eruption on the lower extremities
• Typically appears after prolonged walking or standing, especially in hot weather
• Often seen in tourists at theme parks (hence the name "Disney rash")
• Usually affects the lower legs above the sock line
• Presents as erythema that may evolve into purpura or petechiae

Pathophysiological Basis for Unilateral Presentation

The unilateral presentation of Disney rash can be explained by several factors:

• Differential vascular compromise: One leg may experience greater vascular stress due to:

  • Pre-existing venous insufficiency in one limb
  • Asymmetric walking patterns or weight distribution
  • Previous injury affecting circulation in one leg

• Localized inflammatory response: The inflammatory cascade that triggers vasculitis can be initiated locally and remain confined to one extremity 1

• Differential exposure: Environmental factors may affect one leg more than the other:

  • Sunlight exposure on one side of the body
  • Contact with irritants on one leg
  • Mechanical friction or pressure differences

Differential Diagnosis for Unilateral Leg Rash

When evaluating a unilateral rash on the leg, consider these alternatives:

1. Contact dermatitis: May present unilaterally due to localized exposure to irritants or allergens 2

2. Cellulitis: Typically unilateral, but accompanied by warmth, tenderness, and systemic symptoms

3. Drug-induced eruptions: Can occasionally present asymmetrically 3, 4

4. Tinea corporis/pedis: Can affect one leg more severely than the other 5

5. Rocky Mountain Spotted Fever: Although typically bilateral and centripetal, rash patterns can be variable or localized to particular regions 5, 6

Clinical Approach to Suspected Unilateral Disney Rash

1. History:

   • Recent prolonged walking/standing, especially in hot weather
   • Relationship to exercise or activity
   • Presence of pruritus or pain
   • Previous episodes and their resolution pattern

2. Physical examination:

   • Distribution: Above sock line, sparing areas covered by socks/shoes
   • Morphology: Erythematous macules/patches that may evolve to petechiae
   • Check for temperature difference between legs
   • Assess for edema or signs of venous insufficiency

3. Diagnostic considerations:

   • If accompanied by fever, consider infectious etiologies 7
   • If persistent beyond expected timeframe (typically resolves in 7-10 days), consider biopsy

Management of Disney Rash

Treatment is generally supportive:

• Rest and elevation of the affected leg(s)
• Cool compresses
• Topical corticosteroids for symptomatic relief
• Antihistamines for pruritus
• Prevention strategies for future episodes:
  • Compression stockings during prolonged activity
  • Regular breaks and leg elevation during extended walking
  • Adequate hydration

Common Pitfalls

• Misdiagnosis as cellulitis: Disney rash is often misdiagnosed as cellulitis, leading to unnecessary antibiotic treatment
• Overlooking unilateral presentation: Clinicians may dismiss the diagnosis if only one leg is affected
• Failure to consider vascular status: Underlying venous insufficiency may predispose to unilateral presentation and should be assessed
• Attributing to other causes: The temporal relationship to exercise or prolonged standing is key to diagnosis

While bilateral presentation is more typical, unilateral Disney rash should remain in the differential diagnosis for patients with appropriate history and clinical features limited to one leg.