Evaluation of Splenomegaly


The spleen is a secondary lymphoid organ that lies in intraperitoneally in the left hypochondrium, abuting the diaphragm. It spans from the 9th to 11th rib and weighs between 150-200g. Spleen is supplied by the splenic artery and drains into portal circulation via the splenic vein. It is a part of reticuloendothelial system, immune system and is a site of in utero haematopoiesis. The spleen is enlarged in a diverse set of disease of the above mentioned  systems and in portal hypertension.

Normal Functions of the Spleen

The normal functions of the spleen include

  1. Reticuloendothelial functions: The spleen as a component of the reticuloendothelial system is involved in clearing the blood of ageing or damaged erythrocytes, antibody coated cells and opsonised bacteria. It also removes particles from red cells. The spleen ensures that the red cell in circulation have adequate deformability for passage through microcirculation.
  2. Immune Functions: The spleen is a part of the immune system and plays a role in mounting the immune response . Splenectomy increases the risk of infections particularly with capsulated organisms (see Overwhelming Post-Splenectomy Infection (OPSI)).
  3. Haematopoiesis: Spleen is the site for haematopoiesis in utero. In extrauterine life spleen can become a site of haematopoiesis in disease.

Palpating the Spleen

  1. Palpation of the spleen should start from the right iliac fossa. If this is not done there is a risk of missing a massively enlarged spleen.
  2. Move towards the left costal margin in a direction perpendicular to the margin. Move with each breath. At every position ask the patient to take a deep breath. The tip of the spleen will hit your palpating finger.
  3. If the spleen does not hit your finger move your palpating finger to a position closer to coastal margin, ask the patient to take a deep breath and repeat the procedure described above till your finger hits the costal margin.
  4. If the spleen is felt measure the perpendicular distance between the tip and the left coastal margin. Also note the texture and presence of tenderness.
  5. If the spleen is not felt repeat the procedure with patients lying on right side.
  6. Large spleen can rupture with aggressive palpation. The spleen lies directly under the anterior abdominal wall. One does not need to be aggressive.

Causes of Splenomegaly

The spleen enlarges from the left coastal margin in the direction of the umbilicus. It needs to enlarge 2-3 times before it is palpable. Splenomegaly may be caused be increase in portal venous pressure, infiltrative conditions or when the spleen function needs to increase. Clinically it is useful to classify splenomegaly by size. Massive splenomegaly is enlargement of the spleen beyond the umbilicus. The causes of massive splenomegaly include

  1. Malignant: Chronic myeloid leukaemia, Idiopathic myelofibrois, hairy cell leukaemia, splenic marginal zone lymphoma, chronic lymphocytic leukaemia, prolymphocytic leukaemia
  2. Infections: Tropical splenomegaly, AIDS with Mycobacterium avium complex infections, Kala-azar (visceral leishmaniasis)
  3. Others: β-Thalassaemia major and intermedia, Extrahepatic portal venous obstructions,megaloblastic anaemia, diffuse splenic haemagiosis

The causes of splenomegaly include the above and the following

  1. Portal Hypertension: Cirrhosis, Budd-Chairy syndrome, splenic vein thosmbosis, congestive heart failure, hepatic schistosomiasis
  2. Increased splenic function:
    1. Increased functional demands: Haemolytic anaemia commonly hereditary spherocytosis, autoimmune haemolytic anaemia, β-thalassaemia, early sickle cell anaemia, sickle cell β-thalassaemia,
    2. Infections:
      1. Bacterial: Septicaemia, bacterial endocarditis, splenic abscess, brucellosis, tuberculosis, AIDS with Mycobacterium avium complex infections, secondary syphilis
      2. Viral: Viral hepatitis, infectious mononucleosis, cytomegalovirus,
      3. Parasitic: Malaria , Kala-azar (visceral leishmaniasis), Trypanosomiasis,
      4. Fungal: Histoplasmosis
    3. Immune Disorders:
      1. Autoimmune diseases: Rhumatoid arthritis (Felty’s syndrome), systemic lupus erythrmatosis
      2. Other immune disorders: Immune haemolytic anaemia, immune neutropenia, drug reaction, serum sickness, sarcoidosis
      3. Haemophgocytic lymphohistiocytosis
  3. Infiltrations
    1. Haematological Malignancy:
      1. Myeloid: Chronic myeloid leukaemia, myeloproliferative disease, idiopathic myelofibrosis, polycythaemia vera
      2. Lymphoid: Acute lymphoblastic leukaemia, hairy cell leukaemia, chronic lymphocytic leukaemia, prolymphocytic leukaemia, splenic marginal zone lymphoma, angioimmnoblastic T cell lymphoma
      3. Other: Histiocytosis X, eosinophilic granuloma
    2. Storage disorders:Gaucher disease, Niemann-Pick, Tangier disease, mucopolysachroidosis
    3. Other Infiltrations: Amyloid
  4. Others: Iron deficiency anaemia

 

History and Physical Examination

  1. Fever: Fever is a feature of splenomegaly due to infections, inflammations or malignancy, particularly haematological malignancy. Usually the fever is low grade. High grade fever suggests splenic abscess.
  2. Painful splenemegaly: The nature of pain associated with splenomegaly varies with the cause of splenomegaly.
    1. An enlargement spleen from any cause can cause a dragging pain in the left upper quadrant.
    2. Acute pain left upper quadrant pain is a feature of is a feature of splenic infarct and splenic abscess. Sickle Cell anaemia is associated with small fibrotic spleen because of repeated splenic infarcts. Early in disease the spleen enlarges. Patients may present with acute pain from splenic infarcts. Enlarged spleen from any cause is predisposed to infarction. Acute pain in the left upper quadrant is also a feature of acute splenic abscess.
    3. Splenic vein thrombosis can cause splenomegly and pain in left upper quadrant or epigastric region. It may also cause generalised abdominal pain.
    4. Pancreatitis presents with abdominal pain and can cause painful splenomegaly secondary to splenic vein thrombosis.
    5. Alcohol induced pain is an uncommon but unique feature of Hodgkin lymphoma. Spleen is a common site of involvement by Hodgkin lymphoma. Such patients may have alcohol induced pain in an enlarged spleen.
  3. Pallor: Pallor in a patient with splenomegaly suggests a diagnosis of haemolytic anaemia, haemolymphatic malignancy and infective endocarditis.
  4. Clubbing: Clubbing with splenomegaly is a feature of infective endocarditis and cirrhosis of the liver.
  5. Skin rash: Skin rash in a patient with splenomegaly is seen in systemic lupus erthomatosis, infective endocarditis, lymphoma (angioimmuniblastic T Cell lymphoma, mycosis fungiodes, skin involvement with lymphoma) and drug reaction.  Each of these conditions have a distinct type of rash.
  6. Skin Pigmentation: Hyperpigmantation suggests be seen in hemachromatosis or megaloblastic anaemia. The patients with megaloblastic anaemia may also have knuckle pigmentation.
  7. Jaundice: Jaundice with enlarged spleen is a feature of haemolytic anaemia. The jaundice is usually achloruric. Patients with haemolytic anaemia are predisposed to gallstones. Obstruction of the biliary system from a calculus dislodged from the gall bladder can cause obstructive jaundice with abdominal pain and signs of acute inflammation. Splenomegaly with jaundice is a feature of advanced cirrhosis. Patients with advanced cirrhosis almost always have ascites.
  8. Lymphadenopathy: The enlargement of lymph nodes and spleen is a feature of lymphoid malignancies or diseases that stimulate the lymphoid systems viz. infections and autoimmune diseases and lymphoid malignancy.
  9. Joint symptoms: Arthropathy with splenomegaly suggests the diagnosis of rheumatoid arthritis, systemic lypus erythrmatosis or haematochromatosis.
  10. Oral symptoms: infectious mononucleosis is charecterized by pharyngitis and generalised lymphadenopathy. Bleeding gums and/or gum hypertrophy suggests a diagnosis of leukaemia. Lymphoma can cause tomsillar enlargement. Amyloid is charectetized by macroglossia.
  11. Evidence of Portal Hypertension and Liver Cell Failure: Patients with portal hypertension often have history of haemetemesis. Examination may reveal periumbilical veins (capital medusae), anterior abdominal or flank veins. Patients with evidence liver cell failures with portal hypertension (e.g. jaundice, ascites, spider angiomas, asterxis etc. see Portal Hypertension) have cirrhosis. When the jugular venous pressure is high a diagnosis of congestive cardiac failure should be considered.

Laboratory Evaluation

Haemogram; The haemogram is the most important laboratory test in evaluating a patient with splenomegaly. The significance of findings on haemogram is described in the table below.

Haemogram Finding Conditions
Pancytopenia Hypersplenism, Lymphoma (splenic marginal zone lymphoma), Hairy cell leukaemia, Myelofibrosis, systemic lupus erythrmotosis
Neutrophilic Leucocytosis Acute infections, inflammation
Leucocytosis with premature white cells Chronic myeloid leumaemia, Myeloproliferative disease, Myeloproliferative/Myelodysplastic overlap, Acute lymphoblastic leukaemia
Leucoerythroblastic anaemia Idiopathic myelofibrosis, Bone marrow infiltration
Polycythaemia Polycythaemia vera
Atypical Lymphocytes Infectious mononucleosis
Thrombocytosis Myeloproliferative disease (Chronic myeloid leukaemia, idiopathic myelofibrosis, polycythaemia vera), chronic infections like tuberculosis
Parasites Malaria, bartonelosizs, babesiosis

Other investigations are dictated by the clinical presentations. Commonly performed investigations include biochemistry, microbiology, echocardiography, endoscopy and biopsy of any lymph node or any other mass. Other investigation may be performed as indicated

Imaging

Imaging is an important aspect of evaluation of the spleen but is beyond the scope of this article. Several good reviews exist e.g Singapore Med J 56(3):133-144.

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The BCR-ABL1 Gene


CML Pathogenesis-600pxBCR-ABL1 is a fusion gene formed as a result of the t(9;22)(q34;q11) chromosomal translocation, the translocation that results in the formation of the Philadelphia chromosome. The Abelson murine leukaemia viral oncogene homolog 1 (ABL1) gene from 9q34 is translocated downstream to a region at 22q11 known as breakpoint cluster (BCR). The fusion gene encodes for a constitutionally active tyrosine kinase that has been shown to drive the expression chronic myeloid leukaemia phenotype. BCR-ABL1 gene has also been on implicated in the pathogens is of acute lymphoblastic leukaemia and in rare cases of acute myeloid leukaemia. The gene has been targeted with unparalleled success by the first tyrosine kinase inhibitor approved in clinical practice, imatinib.

 Molecular Biology of BCR-ABL

The ABL1 proto-oncogene is located on chromosome 9 at q34. Chromosome 22 has the BCR gene at 22q11. The ABL1 gene translocated downstream to the BCR gene as a result of the t(9;22)(q34;q11) translocation. ABL1-BCR translocation also occurs and may express but is of no clinical significance.

 

Molecular Biology of CML

The BCR-ABL1 fusion gene and it’s variants

The breakpoint of the ABL1 gene may be upstream exon 1a, between exon 1a and 1b or downstream exon 1b but it is almost always upstream exon 2. With rare exceptions all transcripts of BCR1-ABL1 gene have exon 2-11 of the ABL1 gene. The BCR breakpoints are variable and determine the size as well as the pathogenic properties of the BCR-ABL1 gene.. The breakpoint on the BCR gene are clustered in three regions known major cluster, minor cluster and micro cluster (Table 1). Depending on the location of breakpoint  on the BCR gene three types of protein are synthesized. The p210 transcript is associated with CML and some patients with Philadelphia positive acute lymphoblastic leukaemia. The shorter p190 transcript is associated with philedelphia positive acute lymphoblastic leukaemia and some patients of chronic myeloid leukaemia. The CML that carry this mutation show monocytosis and have a more aggressive course. The p230 is the largest and the rarest of the BCR-ABL1 transcripts. It is associated with a more indolent course and is found in patients with the rare chronic neutrophilic leukaemia. Atypical transcripts e1a3, e13a3 and e6a2 have been described.

Table 1: The BCR-ABL1 fusion genes

 Major Cluster  Minor Cluster  Micro-Cluster
 Synonym M-Cluster m-cluster µ-cluster
Location exons 12-16 Between alternative exon 2, e2’ and e2 between exons e19 and e20
Protein p210 p190 p230
Associated Leukaemia  CML, e14a2 shown to have thrombocytosis in some studies., Ph+ ALL  Ph + ALL; CML that tends to have monocytosis and an agressive course  Chronic Neutrophilic Leukaemia, Small reports describing patients with a course resembling classical CML

Mutagenicity of BCR-ABL1

ABL1 is a nuclear kinase whose activity is tightly regulated by the cell. BCR-ABL1 translocation results loss of regulation and the kinase is  cosntitutively active. Sustitution of ABL1 at the N termnal by segments of the BCR gene result in the synthesis of a protein that has the capacity to dimerise. Dimerisation transphosphorylates and then aurtophsophorylates the the kinase fully activating it. The precise mechanism how BCR-ABL1 leads to chronic myeloid leukaemia is not known but activation of  phosphatidylinositol kinase, RAS/Mitogen activated protein kinase and JAK/STAT pathway has been demonstrated in BCR-ABL1 positive cells. These pathways are involved in cellular growth and differentiation. The BCR-ABL1 kinase also phosphorylates proteins involved in adhesion and migration and this may have a role in premature release of myeloid cells in circulation. CML cells have a two to sixfold increase in reactive oxygen species and have impaired DNA repair. Reactive oxygen species can induce DNA double strand breaks. The results is additional mutations and these are believed to be responsible for blast crisis and acclerates phase.

Tyrosine kinase inhibitors targeting the BCR-ABL1 protein induce a remission in most patients of CML. About half the patients who have achieved sustained complete molecular response relapse on discontinuation of the tyrosine kinase inhibitors. This suggests that the stemat least some CML stem cells are not BCR-ABL1 dependent for growth. Experimental observations support this hypothesis.

Targeting the BCR-ABL1 Gene

The BCR-ABL1 gene was the first gene to be targeted by a tyrosine kinase inhibitor, imatinib. Imatinib was followed by dasatinib, nilotinib, Busotinib and Panotinob. Imatanib, Dasatinib and Nilotinib are approved to first line use. Imatinib has resulted in a 85% 8 year survival. Dasatinib and nolitinib are active in imatinib resistant CML and are now approved for first line use. Drug resistance results from mutations in BCR-ABL1 kinase. The T315I mutation or the gatekeeper mutations impaires access of TKIs to the BCR-ABL1 kinase making most drugs inactive. Panotinib can inhibit the T315I mutation.

 

Further Reading

Barnes DJ Melo JV. Molecular Basis of Chronic Myleoid Leukaemia. In Chronic Myeloproliferative Disorders: Cytogenetic and Molecular Anomalies. Bain Barbra J (Ed) 2003.

Bendamustine


Bendamustine is a mechlorethamine derivative synthesised by Ozegowski and Krebs from the former East Germany in 1963. The  molecule has three parts,

  1. The alkylator mechloethamine,
  2. Benzimidazole ring that mimics purines
  3. Butyric acid side chain.

Each of these part has potential anti-malignacy action but only the alkylating actions are of clinical significance.

Mechanism of Action

Bendamustine acts as a classical chlorethyl alkylating agent. It causes inter and intrastrand DNA cross links that result in DNA strand breaks. The number of DNA strand breaks caused by bendamustine is grater than those caused by cyclophosphamide or melphalan. In addition the breaks are repaired slowly. This is probably because of the bulky structure of bendamustine. It has a partial cross sensitivity against other alkylating agents.

The benzimidazole side chain mimics purines and butyric acid side chain can react with membranes and proteins.  These actions do not contribute to the anti-tumour effect of bendamustine.

Mechanisms of Resistance

Resistance to bendaustime may develop because  of

Increased activity of DNA repair enzymes

Increased expression of sulfhydryl proteins, e.g. glutathione and glutathione-related enzymes

Bendamustine is partially cross-resistance with other alkylators.

Pharmacokinetics

  1. Absorption and Distribution: Bendamustine has a high oral bioavailability of 90% but no oral preparation is available. It is tightly (94%-96%) bound to human serum plasma proteins. Protein binding is not affected by hypoalbuminaemia.  It does not appear to displace other drugs or be displaced by other drugs. It is mainly distributed in the extracellular space and has a steady state volume of distribution of 25 L.
  2. Elimination: It is metabolised by hydrolysis. Active metabolites are formed as a result of drugs metabolism but theses have little clinical significance.  The half-life after a 30 minute infusion is 40 minutes with clearance of 700ml/min.
  3. Effect of Renal Impairment: Renal impairment with creatinine clearance unto 40 ml/min does not affect the elimination of bendamiustine. The effect of more severe renal failure is not studied.
  4. Effect of Hepatic Impairment: Mild Hepatic impairment does not have an effect on bendamustine elimination. The effect of moderate and severe liver impairment is unknown.

Toxicity

  1. Myelosupression: The main toxicity is myelosupression with about half the patients having grade 3 or 4 neutropenia. The incidence of febrile neutropenia is about 7%. Grade 3  to 4 thromboctopenia is about 24%. Anaemia is less common.
  2. Nausea and vomiting is usually mild to moderate
  3. Infusion reactions: infusion reaction is characterised by fevers, hypotension, back and muscle pain, chills, and rigours and may be seen within the 24 hours of infusion. It may be seen unto the third cycle. Steroids may help in patients getting infection reactions.
  4. Skin Toxicity: Skin rash and bullous exanthema
  5. Tumour lysis syndrome
  6. Carcinogenicity: Bendamustine has been associated with myelodysplastic syndrome and acute leukaemia.

Indications

  1. Chronic Lymphocytic leukaemia
  2. Low grade non-Hodgkin lymphoma
  3. Other disease wherebendamustine is used but the role is not established:
    1. Multiple Myeloma
    2. Acute Leukaemia
    3. Solid Tumours – breast cancer, small cell lung cancer, germ cell tumour

Dose

  1. Chronic Lymphocytic leukaemia:
    1. Single Agent: 100mg/m2 day 1 and 2 every 4 weeks
    2. With rituximab: 90mg/m2 day 1 and 2 when used with rituximab
  2. Non-Hodgkin Lymphoma:
    1. Single Agent: 120mg/m2 day 1 day 2 of a 21 day cycle.
    2. With Rituximab:  90mg/m2 o day 1 and day 2 of a 28 day cycle

Dosing in Special Populations

  1. Pregnancy:  Bendamustine is mutagenic.
  2. Paediatric Patients: Safety of bendamustine in paediatric population is not established
  3. Renal Failure: Bendamustine should not be used in patients with creatine clearance of less than 40ml/min
  4. Hepatic failure: Bendamustine should not be used in patients with moderate or severe hepatic impairment (bilirubin >3 X upper limit of normal or bilirubin 1.5-3 X upper limit of normal with AST or ALT 2.5-10X normal)

 

Hydroxyurea – Drug Information


Hydroxyurea was synthesised in Germany in 1860 and was found inhibit granulocyte production. It was only a hundred years after this that its potential as an anticancer drug was realized.

Hydroxyurea Mechanism of Action

Mechanism of Action of Hydroxyurea

Hydroxyurea enters the cell by passive diffusion. It inhibits of ribonucleotide reductase (RR). RR converts ribonucleotide diphosphates to deoxyribonucleotide diphosphates. Deoxyribonucleotide diphosphates are converted to deoxyribonucleotide triphosphates  and incorporated into DNA. Depletion of deoxyribonucleotide triphosphates results in impaired DNA synthesis. RR has two subunits M-1 and M2.  The M-2 subunit is the catalytic subunit and contains iron. Hydroxyurea inhibits RR by chelating iron. Hydroxyurea is an S phase specific drug. The cells exposed to hydroxyurea progress normally through the cell cycle, have a normal G1-S transition but accumulate in the S phase because of an inability to synthesise DNA. They then undergo apoptosis by p53 dependent and independent mechanisms.  Hydroxyurea may be transformed to nitric oxide. Nitric oxide is also an inhibitor of RR and may be responsible for drugs ability to induce foetal haemoglobin. This is important for treatment of sickle cell anaemia. Resistance to HU develops by elevated cellular activity of RR.

Pharmacokinetics of Hydroxyurea

Oral bioavailability of hydroxyurea is 80-100%. Parenteral formulation has no advantage over oral formulation. The drug is well distributed. It enters breast milk, cerebrospinal fluid and third space collections. The ratio of plasma to CSF levels is 4-9:1 and plasma to ascites levels is 2-7.5:1. The elimination half-life is 3.5-4.5 hours. Renal elimination is the main pathway of elimination. Sixty to eighty per cent of the dose eliminated by kidney unchanged. Patients with creatinine clearance of 10-50ml/hr should receive 50% and those with creatinine clearance of less than 10ml/hr should receive 20% of the planned dose. Hydroxyurea is metabolized but the metabolic pathways are not known.

Indications

  1. Myeloproliferative diseases
    1. Chronic myeloid leukaemia
    2. Essential thrombocytosis
    3. Polycythaemia Vera
  2. Acute leukaemia to control counts
  3. Sickle cell anaemia

Dose

Myelosuppression is the dose limiting effect of hydroxyurea. The dose of hydroxyurea needs to be titrated to the leucocyte and platelet counts. The acceptable lower limits of these counts will depend on the indication but generally speaking a leukocyte count less than 2.5X109/L or a platelet count less than 100X109/L is an indication for discontinuing therapy. With the abovementioned provisions in mind the dose of hydroxyurea for different indications are as follows:

  1. Myeloproliferative diseases: The usual dose is 20-30mg/kg/day.
  2. Acute leukaemia: 50-100mg/kg per day
  3. Sickle cell anaemia: 15-20mg/kg/day

Drug interactions

  1. HU inhibits formation of deoxynucleotides and enhanced the effect of agents damaging the DNA, as no nucleotides are available for repair. The effects of purine and pyrimidine analogues. When hydroxyurea is combined with any of these agents it should be done as a part of a protocol whose toxicity has been evaluated. This will prevent unacceptable toxicity.
  2. It has been shown to be synergistic with agents damaging the DNA like cisplatin, alkylating agents and topoisomerase II inhibitors.
  3. It has been used as a radiosensitizing agent in the treatment of head and neck and cervical cancer. It depletes the deoxynucleotide pool needed for DNA repair after radiation-induced damage.
  4. Enhanced anti HIV activity of azidothymidine, dideocytidine and dideoxyinosine

Toxicity

  1. Myelosuppression: The dose limiting toxicity of hydroxyurea is myelosuppression. Hydroxyurea causes rapid fall in leucocyte counts. When used in non-haematological malignancies the fall in leucocyte counts is evident by days 2-5. When used in patients with leukaemia the fall is evident faster, sometimes within a day. This property of hydroxyurea is useful in myeloid leukaemia with very high leucocyte count. Hydroxyurea is the treatment of choice for patients with chronic myeloid leukaemia presenting with very high counts. Though used in acute myeloid leukaemia with hyperleucocytosis, benefit from its use has not been proven in clinical trials.
  2. Gastrointestinal: Oral ulceration and gastrointestinal tract effects may be seen in some patients. They are particularly common in patients who receive chemoradiation with hydroxyurea.
  3. Skin: Dermatological changes may be seen with prolonged use. These include
    1. Skin Pigmentation and rash: Hyperpigmentation, erythema of the face and hands, diffuse maculopapular rash and dry skin. Severe reactions may resemble lichen planus.
    2. Nail Changes: The nails may show atrophy and formation of multiple pigmented bands.
    3. Leg Ulcers: Leg ulcerations may be seen in patients with prolonged therapy with hydroxyurea.
    4. Alopecia: Alopecia may occasionally be seen with the use of hydroxyurea
    5. Radiation Recall: Erythema or pigmentation of previously radiated skin may be seen in some patients.
  4. Mutagenicity and Teratogenicity: Hydroxyurea is a proven teratogen and contraindicated in women are pregnant or are planning a pregnancy. Women in the reproductive age group must be advised about contraception. The carcinogenic potential of hydroxyurea is uncertain. In view of the mechanism of action it is prudent not to use hydroxyurea for non-malignant disease.

Hyperleukocytosis and Leukostasis


Leukostasis is a oncological emergency seen in patients with leukaemia who present with pronounced leucocytosis. It is seen in about 5-30% of adult acute leukaemia cases. It results from slugging of microcirculation by leucocytes.  It is associated with a mortality of 20-40%.

Pathogenesis of Leukostasis

Manifestations of leukostasis result from impaired circulation in the affected vascular bed. Leukocytosis impairs circulation because of

  1. Increased viscosity
  2. Formation of intravascular leukocyte aggregates (white bland thrombi)
  3. Increased adhesion of blasts to the endothelium

Cells increase the viscosity of blood hampering flow through microcirculation. Pliability of blood cells is important for maintaining blood flow in microvasculature. The biconcave shape of the erythrocytes provides them with deformability allowing smooth passage through the microvasculature. Leukocytes are less pliable than erythrocytes.  Normally the number of leucocytes is a small fraction of the number of erythrocytes. The contribution of leucocytes to blood viscosity in minimal.

Blood viscosity increases with leucocytosis. The increase is related to the leucocyte count, size of the leukocytes and the deformability of the leucocytes. Blasts are less deformable than mature cells. Myeloblasts are larger and less deformable than lymphoblasts. Cells of the monoblastic series are the least deformable. Lymphocytes are the smallest and have the least impact on the viscosity amongst all leucocytes.

Blasts secrete cytokines like IL-1β  and TNF-β. These lead to up regulation of adhesion molecules like ICAM-1, VCAM-1 and E-selectin that increases the adhesion of blasts to the endothelium. Adhesions of blasts to microvasculature further diminish blood flow.

The vascular beds most commonly affected are the lung, CNS and the eye. Tissue hypoxia resulting from impaired circulation is believed to contribute to elevated LDH seen in acute leukaemias. 

Clinical Features

About 5-13% of acute myeloid leukaemia and 10-30% of acute lymphoblastic leukaemia have hyperleukocytosis. The symptoms of leukostasis are related to the ischaemia in the affected circulatory bed. The commonest vascular beds affected and the symptoms attributable to these beds are listed below.

Organ Manifestation
Brain Stupor
Eyes Blurring of vision
Lungs Dyspnoea
Kidney Azoaemia
Heart Arrhythmia
Penis Priapsim

Examination of the fundus shows papilledema, blurred disc margins, dilated blood vessels, and retinal haemorrhages.

The leukocyte count  at which symptoms develop depends on the type of leukaemia. Symptoms develop at the lowest counts in acute myeloid leukaemia. Patients of chronic lymphocytic leukaemia may not have symptoms of hyperleukocytosis at leucocyte counts as high as 400X109/L. Leukostasis is associated with increased morbidity and mortality.

Diagnosis

Leukostasis is clinical diagnosis of exclusion. It should be considered in any patients with lung or CNS symptoms who has hyperleukocyosis. Hyperleukocytosis has been variably defined as a count of 50X109/L or 100X109/L. Symptoms are likely to occur at lower counts in patients with acute myeloblastic leukaemia particularly when there is a monocytoid component. Patients with chronic lymphoblastic leukaemia tolerate counts as high as 400X109/L without symptoms. The conditions that can mimic leukostasis include

  1. Pulmonary infection
  2. Pulmonary embolism
  3. Pulmonary oedema
  4. Pulmonary haemorrhage
  5. Transfusion-related acute lung injury  is blood products have been transfused
  6. CNS infections – meningitis and encephalitis
  7. Conditions causing acute mental status change

The x-ray findings include diffuse interstitial or alveolar infiltrates. It can be normal in early stages. Examination of the fundus is important.

Treatment

Leukostasis is associated with a mortality of 20-40%. The treatment of leukostatsis is to rapidly reduce the leukocyte count. Three methods of rapidly reducing leucocyte counts are induction chemotherapy, leukocytopheresis or low dose chemotherapy. Each of these methods are supported by theoretical arguments. Induction chemotherapy is the definitive therapy for leukaemia. Whether leukocytopheresis or hydroxyurea add to the benefit of induction chemotherapy is not clear. The use of hydroxyurea and leukocytopheresis is dictated by the experience of the treating centre. The procedures are usually resorted to with the belief that induction therapy with a very high leucocyte count may increase the risk of tumour lysis. 

Leukocytopheresis: Leukocytopheresis is used because it rapidly brings down the leucocyte count without causing lysis of blasts. It has the theoretical advantage of reducing the risk of tumour lysis and reducing mortality. This has never been proven in clinical trials. Two procedures needed about 12-24 hour apart. Leukocytopheresis is indicated in

  1. Symptomatic patients with AML with leucocyte counts more than 50X109/L and ALL with counts more than 150X109/L.
  2. Asymptomatic patients with AML and leucocyte  counts >100 X 109/L
  3. Asymptomatic patients with ALL with leucocyte counts >300 X 109/L
  4. CML patients who are symptomatic with leucocyte counts greater than 150X109/L,
  5. CLL patients who are symptomatic with leucocyte counts greater than 500X109/L. 
  6. It should not be performed in patients with acute promyelocytic leukaemia symptomatic or asymtomatic

The procedure involves insertion of a catheter. This may be associated with an increased risk of bleeding as these patients have thrombocytopenia.

Low Dose Chemotherapy: Like leukocytopheresis the value of low dose chemotherapy has not been proven. The following interventions may be used (with leukocytopheresis)

  1. Acute myeloid leukaemia should be treated with hydroxyurea in a dose of 50-100mg/Kg. It may be administered as a single or multiple doses.
  2. Acute lymphoblastic leukaemia may be treated with steroids with or without vincristine. 

Induction chemotherapy: Induction chemotherapy is the definitive therapy for acute leukaemia. High counts are associated with a higher risk of tumour lysis resulting in an apprehensions of starting chemotherapy in patients with very high leucocyte counts.

Other measures: Cranial irradiation and dexamethasone has been used in patients with CNS symptoms. Blood transfusions can increase viscosity and may worsen symptoms of leukostasis. One needs to be conservative about red cell transfusions till the leukocyte counts become normal. Transfusions in patients with symptoms attributable to anaemia should not be held back. 

 

Leukaemia – The Peripheral Smear


Differentiating Acute and Chronic Leukaemia

Leucocytosis with anaemia is a feature of acute and chronic leukaemia. It is possible to differentiate acute and chronic leukaemia by looking at the peripheral smear. Patients with acute leukaemia often have thrombocytopenia. Patients with chronic lymphocytic leukaemia may have normal or low platelet counts. Patients with chronic myeloid leukaemia have normal or high platelet counts.

Haemoglobin Platelets Peripheral Smear
Acute Leukaemia Low Low Immature forms other than blasts not seen
Chronic Lymphocytic Leukaemia Low or Normal Low or Normal Normal looking lymphocytes
Chronic Myeloid Leukaemia Low or Normal Normal or High Immature leucocytes, all phases of leucocyte maturation seen

The phases of maturation of myeloid cells (from the least to the msot mature) are blasts, promyelocytes, myelocytes, metamyelocytes, band form and mature granulocyte (see Myeloid Precursors Morphlogy). The peripheral smear from patients with acute leukaemia shows blasts (or promyelocytes) and mature neutrophils. Very few cells, if any, with maturity between the two stages that occupy two ends of the spectrum are seen. Patients with with chronic myeloid leukaemia have cells with all stages of maturity between blasts and mature granulocytes. The peripheral smear in patients with acute leukaemia shows mature lymphocytes.

The explanation for the different peripheral smear findings in acute leukaemia and chronic myeloid leukaemia is in the pathogenesis of the two diseases. Chronic myeloid is a myeloprolferative disease. It is a clonal disease. The stem cells of patients with chronic myeloid leukaemia carry the BCR-ABL mutation. This mutation results in clonal expansion. All blood cells in a patient arise from one clone. The release of cells from the bone marrow of patients with CML is not limited to mature granulocytes. Some cells leave the marrow and result in leucocytosis.

The marrow of a patient of acute leukaemia has two clone one malignant one normal. The malignant clone can not differentiate beyond the stage of a blast (or promyelocyte). It slowly effaces the normal clone. The mature granulocytes seen in the peripheral smear arise from the normal clone and the blasts from the malignant clone. The normal clone releases cells only when they mature to the stage of band cell or beyond. The malignant clone can not mature beyond the stage of a blast. The stages between blasts and band forms/mature granulocytes are not seen in peripheral smear of acute leukaemia.

Osteonecrosis in Acute Lymphoblastic Leukaemia (ALL)


Corticosteroids are an important component of treatment of childhood ALL. The use of corticosteroids ahs been associated with osteonecrosis. The estimates of osteonecrosis have varied from 7.4%-44%.  About 25% of these patients need surgical intervention for symptom or functional deficit.

Factors Predisposing to Osteonecrosis

  1. Age: Increasing age predisposes to ON. ON is uncommon below the age of 10 years and increases thereafter. The extent of ON is adults with ALL is not characterized.
  2. Gender: Females are at a greater risk of ON than males.
  3. Steroid Use:  ON is more common with the use of dexamethasone. Administering dexamethasone on alternate weeks in late intensification has been shown to be associated with a lower incidence of osteonecrosis. Patients who have a poor  dexamethasone clearance have a higher risk of ON.
  4. Other Factors: ON has been reported to be more common in patients with a low albumin and elevated. High body-mass index is associated with increased risk of ON.

Mechanism of Osteonecrosis

The mechanism of ON in ALL patients is unknown. The proposed etiologies are:

  1. Steroid induced hypercoagulable state resulting in the development of microthrombi
  2. Steroid induced intramedullary lipocyte proliferation and hypertrophy causing a reduced blood flow
  3. Suppression of osteoblasts and apoptosis of osteocytes

Clinical Presentation

The median time to occurrence of symptoms is 14-27 months. Ninety-five percent of the patients have ON of weight-bearing joints The usual presentation if of pain in the hip and knees. In severe cases the joints may collapse.

Management

The treatment of ON is mainly supportive. Surgical intervention, including joint replacement where needed, may be needed in a about one-fourth of the patient for pain or functional deficit.  Bisphosphonates have been used to slow progression but their role is uncertain. The value of discontinuing steroids is not certain but most discontinue steroids but most discontinue steroids.

Prevention and Monitoring

MRI can detect ON before it becomes symptomatic but it’s use outside clinical trials is not recommended.