Risk factors:
(1) female gender
(2) insulin-dependent diabetes
Clinical features:
(1) The initial lesion may be a small red papule.
(2) The typical lesion is a plaque with irregular contour and slightly raised edges that is slowly enlarging.
(3) The lesions are more common in the pretibial and medial malleolar areas and often bilateral. They may occur anywhere on the body, including the scalp.
(4) The periphery is purplish-reddish-blue while the center ranges from erythematous to yellow to brown.
(5) As the lesion evolves it becomes more sclerotic and atrophic and it may develop telangiectasiae.
(6) The lesions are painless and have decreased to absent sensation to touch or pin prick.
Complications:
(1) ulceration
(2) poor healing after trauma (including a skin biopsy site)
(3) secondary infection
(4) rarely squamous cell carcinoma
Pathologic features:
(1) early lesions may show a neutrophilic necrotizing vasculitis while older lesions show a vasculopathy with intimal thickening and fibrosis
(2) pallisading histiocytes with multi-nucleated giant cells in the deep dermis
(3) degeneration of the dermal collagen with hyalinization
Differential diagnosis:
(1) other conditions with pallisading granulomas (granuloma annulare, annular sarcoid, etc).
(2) diabetic dermopathy
(3) dermatophyte infection
