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Livedo Vasculitis
Some vasculitic disorders are characterized by fibrinoid necrosis of the walls of small vessels and by thrombosis. In such
lesions, neutrophilic infiltrates with leukocytoclasia usually are not a prominent feature. Lesions in this category often evolve into areas of frank necrosis of the neighboring dermis and epidermis. They heal with
the formation of small, poorly vascularized scars. The classsic example is livedo vasculitis. This disorder has a predilection for the legs (S8C25P11-1). Livedo vasculitis is a necrotizing, thrombotic vasculitis.
In the acute phase, vessels in the upper portion of the dermis show areas of fibrinoid necrosis (S8C26P12-1-3). Some of the vessels may be dilated (micro-aneurysmal)
and some may be occluded by thrombi (S8C25P11-2). Mild
perivascular infiltrates of neutrophils are a variable, often inconspicuous, feature. In some examples, there is no evidence of an increase in the number of vessels in the affected area; in other examples, the
characteristic vascular changes may be associated with lobular hyperplasias of the type associated with acral angiodermatitis (S8C26P12-4). The vasculitic process may extend along
vessels into the subcutaneous fat (S8C25P11-3).
Samlaska CP, James WD: Superficial thrombophlebitis I. Primary hypercoagulable states. J Am Acad Dermatol 1990;22: 975-89.
Thrombotic Thrombocytopenic Purpura
The lesions of thrombotic thrombocytopenic purpura qualify as a necrotizing, thrombotic angiitis (thrombotic angiopathy). Small vessels are involved;
the vessels show areas of smudgy, fibrinoid necrosis and thrombosis (S8C25P11-4 & 5). The process is a generalized vasculopathy.
Proteinaceous Coagulopathies
The category of the coagulopathies is morphologically heterogeneous. For some examples, the changes are those of a necrotizing, thrombotic angiitis.
For other examples, a proteinaceous, pale acidophilic material accumulates in the lumens of small vessels; the material occludes the lumens of the affected vessels (S8C25P11-6). The affected vessels often are dilated. The nature of
the occluding proteinaceous material is variable. For some examples, the deposits are a manifestation of a cryoglobulinemia (S8C24VA6-1-4). In the anti-phospholipid syndrome, small vessels of the skin contain thrombi (S8C26P12-5-7).
Senile Dermatolysis
Aged skin is fragile; it is easily disrupted by vigorous rubbing or scratching. Defects may be produced in the actinically damaged
reticular dermis in response to physical trauma. The defects, early on, are associated with minimal, inflammatory infiltrates of neutrophils. The defects in the damaged connective tissue of sun-exposed skin are
elongated and angulated; they often are partially outlined by fibrin deposits. These defects may be associated with extravasated red blood cells in the patterns of senile purpura. The defects may persists as such,
or may be inlaid with a delicate, loosely cellular fibrous matrix; the inlay of fibrous matrix contrasts with the surrounding, actinically altered, fibro-elastotic matrix of solar elastosis (S8C26aP12a-1-8).
Grob JJ, et al: Unfading acral microlivedo. J Am Acad Dermatol 1991;24: 53-8.
Itin PH, Winkelmann RK: Cutaneous manifestations in patients with essential thrombocythemia. J AmAcad Dermatol 1991;24:59-63.
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