What is the etiology of Schamberg's purpura?

Etiology of Schamberg's Purpura

Schamberg's purpura is primarily caused by capillary fragility and perivascular inflammation without true vasculitis, resulting in extravasation of red blood cells and subsequent hemosiderin deposition in the skin.

Pathophysiology

• Schamberg's purpura (also called progressive pigmentary dermatosis) is classified as a pigmented purpuric dermatosis characterized by perivascular inflammation and hemorrhage without fibrinoid necrosis of blood vessels 1
• Histologically, there is a superficial perivascular mononuclear inflammatory infiltrate with extravasation of red blood cells in the dermis 2
• The condition features purpuric lesions with "cayenne-pepper" spots, often located on the lower limbs 3

Etiologic Factors

Primary (Idiopathic)

• In many cases, Schamberg's purpura occurs without an identifiable cause and is considered idiopathic 1
• The condition may persist for years without treatment, though spontaneous remission can occur within 1-4 years 2

Secondary Causes

• Medications: Various drugs have been implicated in triggering Schamberg's purpura 1
• Venous hypertension: Increased pressure in lower extremity veins may contribute to capillary fragility 1
• Immune-mediated mechanisms: The perivascular inflammatory infiltrate suggests possible immune system involvement 1
• Infectious triggers: Though not definitively established, some cases may be associated with preceding infections 1

Clinical Presentation

• Presents as macular purpuric and petechial pigmented lesions, often with a characteristic "cayenne-pepper" appearance 1, 2
• Primarily affects the lower extremities but can become generalized in some cases 2
• The condition is chronic and may persist for years, with periods of exacerbation and remission 1
• Typically asymptomatic, though some patients may report mild pruritus 1

Differential Diagnosis

• Must be distinguished from other pigmented purpuric dermatoses including:
  • Lichen aureus (golden-colored lesions)
  • Majocchi's purpura (annular lesions)
  • Gougerot-Blum purpura (lichenoid lesions) 1
• Should also be differentiated from vasculitic purpuras, which demonstrate fibrinoid necrosis of vessel walls on histopathology 1
• Other conditions to consider include thrombocytopenic purpura, which can be ruled out by normal platelet counts 2

Treatment Options

• Treatment options are limited and often provide only partial benefit 1
• Phototherapy has shown promising results:
  • PUVA (psoralen plus ultraviolet A) therapy has demonstrated dramatic responses in some cases 4, 2
  • Narrowband UVB therapy has been effective, particularly in pediatric cases 5
  • Fractional non-ablative 1540 nm erbium:glass laser has shown success in resolving purpuric pigmented rash 3
• Despite treatment challenges, approximately 67% of patients eventually experience clearing of lesions 1

Prognosis

• Schamberg's purpura is a chronic condition that may persist for years 1, 2
• Without treatment, the disease can last up to 7 years in children, though spontaneous remission may occur within 1-4 years 2
• The condition does not typically affect mortality or overall health but may impact quality of life due to cosmetic concerns 1

Key Points for Clinicians

• Diagnosis is confirmed by skin biopsy showing perivascular inflammation and red blood cell extravasation without vasculitis 1, 2
• Laboratory findings are typically normal in primary Schamberg's purpura 2
• Consider medication review in patients presenting with new-onset pigmented purpura 1
• Phototherapy represents a valuable alternative treatment, especially for patients with long-standing and widespread disease 4