Page 329 - Concise Pathology for Exam Preparation ( PDFDrive )

314 SECTION II Diseases of Organ Systems

Q. Write briefly on autoimmune acquired haemolytic anaemia
(AIHA).
Ans. AIHAs are a group of acquired disorders in which antibodies develop against red cell
antigens and cause destruction of red cells.

Classification
1. Based on antibody type
(a) Warm antibody AIHA
(i) Primary or idiopathic
(ii) Secondary
- Drugs (methyldopa, penicillin and quinidine)
- Autoimmune disorders (SLE, others)
- Haematologic malignancies like chronic lymphocytic leukaemia and
lymphomas
(b) Cold antibody AIHA
(i) Cold haemagglutinin disease
(ii) Paroxysmal cold haemoglobinuria
(iii) Cold AIHA associated with mycoplasma infection
2. Based on aetiology
(a) Idiopathic autoimmune acquired haemolytic anaemia (50%)
(b) Secondary autoimmune acquired haemolytic anaemia (50%)
(i) Drugs, eg, methyldopa, penicillins, procainamide and phenothiazine
(ii) Chronic lymphocytic leukaemia
(iii) Malignant disorders like lymphomas
(iv) Infections like M. pneumoniae, infectious mononucleosis, cytomegalovirus and
rubella
(iv) SLE and other connective tissue disorders
(v) Immune deficiency states (common variable immunodeficiency)
(vi) Miscellaneous: Carcinoma, sarcoidosis, ovarian teratoma posttransplant

Warm Antibody AIHA
• Most common form of immune haemolytic anaemia
• Caused by warm antibodies, which react with RBCs at 37°C
• Majority of warm antibodies are of the IgG class
• Most RBC destruction is extravascular. IgG-coated RBCs bind to Fc receptors on mac-
rophages resulting in loss of RBC membrane during passage through spleen. This con-
verts the RBCs to spherocytes, which are removed by the spleen.
• Clinical features include anaemia, jaundice, hepatosplenomegaly and manifestations of
underlying disease.
• Diagnosis is based on presence of anaemia with reticulocytosis, evidence of haemolysis,
spherocytes in peripheral blood and positive direct (antibodies on the red cell surface)
and indirect Coombs tests (antibodies in the serum).

Cold Antibody Autoimmune Haemolytic Anaemia

• Caused by cold agglutinins, which are IgM antibodies that bind and agglutinate RBCs
at low temperatures (0–4°C)
• It is of two types, cold haemagglutinin disease (CHAD) and paroxysmal cold haemoglo-
binuria (PCH). CHAD is characterized by a haemolytic anaemia due to autoantibodies
that act as RBC agglutinins at low temperatures; whereas, PCH is characterized by epi-
sodes of acute haemolysis due to autoantibodies that act as red cell lysins at low tem-
peratures.
• Most cells with bound IgM pick up C3b but are not lysed in the periphery.
• When they travel to warmer areas, the weakly bound IgM is released, but the coated
C3b remains.

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