Clinical Pathology

Anaemia due to Bone Marrow Failure

APLASTIC ANAEMIA

• •Aplastic anaemia is a bone marrow failure syndrome characterized by peripheral pancytopaenia and marrow hypoplasia. Paul Ehrlich introduced the concept of aplastic anaemia in 1888 when he studied the case of a pregnant woman who died of bone marrow failure. However, it was not until 1904 that this disorder was termed aplastic anaemia by Chauffard.
• •Aplastic anaemia is a rare but extremely serious disorder that results when the marrow fails to produce blood cells. Aplastic anaemia may be either acquired or inherited. It is estimated that there are 2 to 12 new cases per million population per year.
• •No racial predisposition exists .  The male-to-female ratio in acquired aplastic anaemia is approximately 1:1. Aplastic anaemia occurs in all age groups

PATHOPHYSIOLOGY

• •The theoretical basis for marrow failure includes primary defects in or damage to the stem cell or the marrow microenvironment. More than 80% of cases are acquired. In acquired aplastic anaemia, clinical and laboratory observations suggest that this is an autoimmune disease.

Morphologically, the bone marrow is devoid of haematopoietic elements, showing largely fat cells.

Suppression of haematopoiesis likely is mediated by an expanded population of the following cytotoxic T lymphocytes (CTLs): CD8 and HLA-DR+, which are detectable in both the blood and bone marrow of patients with aplastic anaemia.

These cells produce inhibitory cytokines, such as gamma interferon and tumor necrosis factor, which are capable of suppressing progenitor cell growth. These cytokines suppress haematopoiesis by affecting the mitotic cycle and cell killing through induction of Fas-mediated apoptosis.

CAUSES OF APLASTIC ANAEMIA

• •Congenital / inherited (20%)

– Occasionally, marrow failure may be the initial presenting feature.

–Fanconi anaemia, Dyskeratosis congenita, Cartilage hair hypoplasia, Pearson syndrome, Amegakaryocytic thrombocytopaenia, Diamond-Blackfan syndrome, Familial aplastic anaemia

• •Acquired (80%)

–Idiopathic

–Infectious causes such as hepatitis viruses, Ebstein-Barr virus (EBV), HIV, parvovirus, and mycobacterial infections

–Toxic exposure to radiation and chemicals such as benzene

–Pancreatic insufficiency.

–Drugs, such as chloramphenicol, phenylbutazone, and gold, may cause aplasia of the marrow. The immune mechanism does not explain the marrow failure in idiosyncratic drug reactions. In such cases, direct toxicity may occur, perhaps due to genetically determined differences in metabolic detoxification pathways.

–Transfusional graft versus host disease

–Liver transplantation for fulminant hepatitis

–PNH is caused by an acquired genetic defect. Approximately 20% of patients with aplastic anaemia have evidence of PNH at presentation.

–Pregnancy

CLINICAL FEATURES

• •The clinical presentation of aplastic anaemia includes symptoms related to the decrease in bone marrow production of hematopoietic cells. The onset is insidious, with the initial symptom relating to anaemia or bleeding, fever or infections.
• •Anaemia may manifest as pallor, headache, palpitations, dyspnoea, fatigue, or pedal oedema.  Thrombocytopaenia may present as mucosal and gingival bleeding or petechial rashes. Neutropaenia may manifest as overt infections, recurrent infections, or mouth and pharyngeal ulcerations .

PHYSICAL EXAMINATION

• •The physical examination may show signs of anemia, such as pallor and tachycardia, and of thrombocytopaenia, such as petechiae, purpura, or ecchymoses. Overt signs of infection usually are not apparent at diagnosis.
• •A subset of patients with aplastic anaemia present with jaundice and evidence of clinical hepatitis.
• •In any case of aplastic anaemia, look for physical stigmata of inherited marrow failure syndromes such as skin pigmentation, short stature, microcephaly, hypogonadism, mental retardation, and skeletal anomalies. A careful examination of the oral pharynx, hands, and nailbeds should be preformed, looking for clues of dyskeratosis congenita.

LABORATORY STUDIES

• •CBC count and peripheral smear

–Hb, PCV reduced; Rapid ESR; Low platelets, total WBC count.

–A paucity of platelets, red blood cells, granulocytes, monocytes, and reticulocytes is found. Mild macrocytosis occasionally is encountered. The degree of cytopaenia is useful in assessing the severity of aplastic anaemia. The corrected reticulocyte count is uniformly low in aplastic anaemia.

–The presence of teardrop poikilocytes and leucoerythroblastic changes is suggestive of an infiltrative process.

• •Peripheral blood

–Haemoglobin electrophoresis and blood group testing may show elevated foetal hemoglobin and red cell I antigen suggesting stress erythropoiesis, which is observed in both aplastic anaemia and MDS and often is proportional to the macrocytosis.

–Biochemical profile, including evaluation of transaminases, bilirubin, lactic dehydrogenase.

–Serologic testing for hepatitis and other viral entities such as EBV, CMV, and HIV

–Autoimmune disease evaluation for evidence of collagen-vascular disease

–The Ham test or sucrose haemolysis test.

–Histocompatibility testing should be conducted early to establish potential related donors, especially in younger patients.

• •Bone marrow aspiration and biopsy

–A bone marrow biopsy is performed in addition to the aspiration so that the cellularity may be assessed both qualitatively and quantitatively. In aplastic anaemia, these specimens are hypocellular.

–Aspirations alone may appear hypocellular because of technical reasons (eg, dilution with peripheral blood), or they may appear hypercellular because of areas of focal residual haematopoiesis.

Histologic Findings – Findings include hypocellular bone marrow with fatty replacement and relatively increased nonhaematopoietic elements such as plasma cells and mast cells. Perform careful examination to exclude metastatic tumour foci on  biopsy.

–A proportion of marrow lymphocytes greater than 70% has been correlated with poor prognosis in aplastic anaemia. Some dyserythropoiesis with megaloblastosis may be observed in aplastic anaemia.

–A core biopsy provides a better idea of cellularity; the specimen is considered hypocellular if it is less than 30% cellular in individuals younger than 60 years or less than 20% in those older than 60 years.

Staging: Based on International Aplastic Anaemia Study Group (Camitta, 1983)

• •Blood

–Neutrophils – Less than 0.5 X 10^9/L

–Platelets – Less than 20 X 10^9/L

–Reticulocytes – Less than 1% corrected (percentage of actual hematocrit [Hct] to normal Hct)

• •Marrow

–Severe hypocellularity

–Moderate hypocellularity with hematopoietic cells representing less than 30% of residual cells

• •Severe aplasia is defined by any 2 or 3 peripheral blood criteria and either marrow criterion.
• •A further subclassification followed the recognition that individuals with neutrophils lower than 0.2 X 109/L constituted a very severe aplastic anaemia (VSAA) group. This group is less likely to respond to immunosuppressive therapy.

MEDICAL MANAGEMENT

Transfusions: Patients with aplastic anaemia require transfusion support until the diagnosis is established and specific therapy can be instituted.

Treatment of infections: Infections are a major cause of mortality in these patients. Empirical antibiotic therapy should be based on local microbial sensitivities .       

Bone marrow transplantation: HLA-matched sibling donor BMT is the treatment of choice for a young patient with severe aplastic anaemia.

Immunosuppressive therapy: Immune suppression as a treatment for aplastic anaemia is especially useful if a matched sibling donor for BMT is not available or if the patient is older than 60 years. The various options include combination therapy, including Anti thymocyte globulin, Cyclosporine A, and methylprednisolone, with or without cytokine support.

Surgical Care : A central venous catheter is required prior to immunosuppressive therapy or BMT

Diet : The diet for the patient with aplastic anaemia who is neutropaenic or on immunosuppressive therapy should be tailored carefully to exclude raw meats, dairy products, or fruits and vegetables that are likely to be colonized with bacteria, fungus, or moulds.

Activity: The patient should avoid the following: Any activity that increases the risk of trauma during periods of thrombocytopaenia; Risk of community-acquired infections during periods of neutropaenia

PROGNOSIS – The outcome of aplastic anaemia has improved significantly with time because of better supportive care. 20% of patients may spontaneously recover with supportive care. The estimated 5-year survival rate for the typical patient receiving immunosuppression is 75% and for matched sibling donor BMT is greater than 90%. However, in case of immunosuppression, a risk of relapse and late clonal disease exists.

PAROXYSMAL NOCTURNAL HEMOGLOBINURIA (PNH)

A rare but potentially serious blood disease that can affect people of any age & sex. Incidence of 1 per 100,000. Acquired defect in the stem cells, that leads to Premature destruction of red blood cells within blood vessels (intra-vascular haemolysis), causing anaemia and dark urine. Tendency for increased thrombosis of veins in the abdomen leading to potentially fatal liver failure. PNH may occur as an isolated disorder or PNH may occur in association with aplastic anaemia and MDS.

Investigations – Pancytopaenia, Hams acid serum test, Sucrose haemolysis test, Flow Cytometry

MYELODYSPLASTIC SYNDROMES

®Refers to a group of clonal stem cell disorders characterized by maturation defects resulting in ineffective haemopoiesis.  There is an increased risk of transformation to AML. Bone marrow is partly or wholly replaced by the population of a mutant multipotent stem cell (pluripotent cell). However the process is both ineffective and disorderly. As a result, the bone marrow is usually hypercellular or normocellular,but the peripheral blood shows pancytopaenia.

MDS- types

A. Idiopathic( primary) Occurs mainly in patients over age 50. Develops insidiously.

B. Therapy – related MDS (t-MDS).

®Occurs as a complication of previous chemotherapy or radiation therapy- appears  2 or 8 years after exposure.

®** all forms of MDS can transform to AML.  ( highest frequency in patients with t-MDS).

MDS- FAB classification

®Refractory anaemia (RA) < 5%

®RA with ring sideroblasts (RARS)< 10%

®RA with excess blasts (RAEB) 5-20%

®RA with excess blasts in transformation( RAEBt) 20-30%

®Chronic myelomonocytic leukaemia (CMML) >30%

Pathogenesis – Unknown;  normo or hypercellular marrow; May arise out of background of stem cell damage.

Morphology –

®Dysplastic differentiation affecting all three lineages.

®Erythroid series: ringed sideroblasts, megaloblastoid change, nuclear budding abnormalities.

®Myeloid series: neutrophils contain decreased number of secondary granules or may have toxic granulation or may exhibit lack of segmentation.

®Megakaryocytic series: single nuclear lobes or multiple separate nuclei.

®Myeloblasts: Increased. Less than 30% of the population.

®Peripheral smear: giant platelets, macrocytes, poikilocytes,  monocytosis. Myeloblasts <10%.

Clinical course – Primary :>more than 60 years of age. Weakness, infections, hemorrhages. 50% are asymptomatic. Median survival: 1-3 yrs in primary. Progression to AML (10 to 40% of individuals). Treatment options are limited. Younger patients- allogeneic bone  marrow transplant.

References : Pathologic Basis of disease – Robbins & Cotran, 7th Ed; General & systematic pathology – Underwood, 4th Ed; Williams Haematology, 6^th Edition, 2001; DeGruchy’s Clinical Haematology in Medical Practice, 5^th Edition, 1999; Wintrobe’s Clinical Hematology. 11^th Edition, 2004; Dacie and Lewis’s Practical Haematology,, 9th Edition, 2001;  Essential Haematology Fourth Edition, 2001. By: A Victor Hoffbrand.