Chapter 23: Cryopathic Hemolytic Anemia

INTRODUCTION

• This type of anemia is caused by autoantibodies that bind red cells best at temperatures below 37°C, usually below 31°C.

• It is mediated through two major types of “cold antibody”: cold agglutinins and Donath-Landsteiner antibodies.

• Clinical features vary considerably, but in both types, the complement system plays a major role in red cell destruction.

COLD AGGLUTININ-MEDIATED AUTOIMMUNE HEMOLYTIC ANEMIA

• Cold agglutinins are immunoglobulin M (IgM) autoantibodies that agglutinate red cells, optimally between 0°C and 5°C. Complement fixation occurs at higher temperatures.

• This hemolytic anemia is classified as either primary (chronic cold agglutinin disease) or secondary (generally as a result of Mycoplasma pneumoniae infection or Epstein-Barr virus [EBV]–related infectious mononucleosis) (Table 23–1).

• Peak incidence for the primary (chronic) syndrome is in persons older than 50 years.

• This disorder characteristically has monoclonal IgM cold agglutinins and may be considered a symptomatic monoclonal gammopathy.

• Some patients develop a B-cell lymphoproliferative disorder (eg, Waldenström macroglobulinemia).

Pathogenesis

• The specificity of cold agglutinins is usually against I/i antigens. I is expressed heavily in adult red cells, weakly on neonatal red cells. The reverse is true of the i antigen, which also may still be expressed on reticulocytes.

• High proportions of IgM cold agglutinins with either anti-I or anti-i specificity have heavy-chain variable regions encoded by V_H4–34, a conserved immunoglobulin variable region gene.

• Naturally occurring cold agglutinins are present in low titer (less than 1:32) in normal persons. Transient hyperproduction of less clonally restricted antibodies occurs in the recovery phase of infections, such as EBV, mycoplasma, or cytomegalovirus.

• I/i antigens serve as mycoplasma receptors, which may lead to altered antigen presentation and to subsequent autoantibody production.

• In B-cell lymphomas, cold agglutinins may be produced by the malignant lymphocytes.

• The highest temperature at which antibodies can cause red cell agglutination is termed the thermal amplitude. The higher the thermal amplitude, the greater the risk of clinically significant hemolysis, depending on the ambient temperature.

• Cold agglutinins bind to red cells in the superficial dermal vessels, where temperatures may be less than 37°C, impeding capillary flow, producing ...