What's New About Canine IMHA?

INTRODUCTION

Antibody and/or complement-mediated destruction of circulating red blood cells (RBCs) is known as immune-mediated haemolytic anaemia (IMHA). The destruction of RBCs occurs by extravascular phagocytosis of these opsonized particles in the spleen or liver, or by intravascular osmotic lysis following the generation of terminal membrane attack complexes of the complement pathway. The former mechanism is most likely to involve IgG antibody, and the latter is more closely associated with the binding of IgM to the surface of the RBCs. Although either intra- or extravascular haemolysis may be dominant in any one patient, it is possible for combinations of these two mechanisms to occur. In some cases, bone marrow erythroid precursors (instead of, or in addition to the circulating erythrocytes) are targeted giving rise to a more severe diseases termed non-regenerative IMHA (NRIMHA) and pure red cell aplasia (PRCA).

The diagnostic label IMHA covers a wide spectrum of clinical disease. The basic distinction is between primary and secondary disease. In primary IMHA no underlying cause for the presence of antibody can be identified on thorough clinical and laboratory investigation. Primary IMHA may therefore be considered as a true idiopathic, autoimmune disease and the diagnostic label autoimmune haemolytic anaemia (AIHA) applied. AIHA and AITP may occur concurrently (Evans' syndrome) or may be part of a multisystemic autoimmune syndrome (e.g. systemic lupus erythematosus). AIHA may also occur in combination with autoimmune neutropenia and sometimes all three immune-mediated cytopenias may be concurrent. By contrast, in secondary IMHA, the presence of erythrocyte-associated antibody is secondary to an underlying cause. […]