A 34-year-old woman notices blue toes and a lacey rash on her knees when outside in the winter months. She has chronic hepatitis C virus infection. She has also noticed weakness, joint discomfort, and red spots on her legs. On examination, she has livedo reticularis-type skin on her thighs, and areas of palpable purpura
on her toes. She has abnormal proteins detected in her serum. Which of the following is the most likely mechanism for the vessel injury seen in this condition?
(A) breakdown of erythrocytes
(B) medium vessel vasculitis
© aggregation of abnormal platelets
(D) temperature-dependent antibodies
(E) cold precipitable proteins
solutions:
(E) The syndrome is caused by cold-precipitable proteins (cryoglobulins) that are found in plasma or serum. These cryoproteins can be of three classes. Type 1 are single component (immunoglobulin G, M, or A [IgG, IgM, IgA]), Type 2 are called “mixed cryoglobulins” (usually IgG molecules complexed with IgM molecules
having anti-IgG reactivity), and Type 3 are polyclonal immunoglobulins with antiimmunoglobulin
activity. Cryoglobulinemia is small vessel vasculitis (not medium), and platelet aggregation is not an important mechanism for the vessel injury.