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Conditions
that cause an abnormal protein content in the blood, typically in
the form of immunoglobulins, can affect vascular fragility and lead
to purpura.
Amyloidosis (see Amyloidosis) causes amyloid deposition within vessels in the skin and subcutaneous tissues, which may increase vascular fragility, producing purpura. In some patients, coagulation factor X is adsorbed by amyloid and becomes deficient, but this usually is not the cause of bleeding. Periorbital purpura or a purpuric rash that develops in a nonthrombocytopenic patient after gentle stroking of the skin suggests amyloidosis.
Cryoglobulinemia produces immunoglobulins that precipitate when plasma is cooled (ie, cryoglobulins) while flowing through the skin and subcutaneous tissues of the extremities. Monoclonal immunoglobulins formed in Waldenström's macroglobulinemia or in multiple myeloma (see Plasma Cell Disorders: Multiple Myeloma) occasionally behave as cryoglobulins, as may mixed IgM-IgG immune complexes formed in some chronic infectious diseases, most commonly hepatitis C. Cryoglobulinemia can lead to small-vessel vasculitis, which can cause purpura. Cryoglobulins can be detected by laboratory testing.
Hypergammaglobulinemic
purpura is a vasculitic purpura that primarily affects women. Recurrent crops of small, palpable purpuric lesions develop on the lower legs. These lesions leave small residual brown spots. Many patients have manifestations of an underlying immunologic disorder (eg, Sjögren's syndrome, SLE). The diagnostic finding is a polyclonal increase in IgG (broad-based or diffuse hypergammaglobulinemia on serum protein electrophoresis).
Hyperviscosity
syndrome (see Plasma Cell Disorders: Symptoms and Signs) resulting from a markedly elevated plasma IgM concentration may also result in purpura and other forms of abnormal bleeding (eg, profuse epistaxis) in patients with Waldenström's macroglobulinemia.
Last full review/revision April 2009 by James N. George, MD
Content last modified April 2009
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