Haematology Flashcards
what is the normal level of haemoglobin and MCV in woman and men?
woman
- Hb: 120 - 165 grams/litre
- MCV: 80-100 femtolitres
Men
- Hb: 130-180 grams/litre
- MCV: 80 -100 femtolitres
what the main categories of anaemia based on size of RBC?
Microcytic - low MCV indicating small RBCs
Normocytic anaemia - normal MCV indicating noral sized RBCs
Macrocytic anaemia - large MCV indicating large RBCs
what are some causes of microcytic anaemia?
thalassaemia anaemia of chronic disease iron deficiency anaemia lead poisoning sideroblastic anaemia
what are some causes of normocytic anaemia?
acute blood loss anaemia of chronic disease aplastic anaemia haemolytic anaemia hypothyroidism
what are the causes of macrocytic anaemia?
macrocytic anaemia can be megaloblastic or normoblastic
megaloblastic anaemia is the result of impaired DNA synthesis - cause by B12 deficiency or folate deficiency
Normoblastic macrocytic anaemia is caused by
- alcohol
- reticulocytosis (usually from haemolytic anaemia or blood loss)
- hypothyroidism
- liver disease
- drugs such azathioprine
what are the general symptoms of anaemia?
tiredness shortness of breath headaches dizziness palpitations worsening of other conditions such as angina, heart failure or PVD
what are some symptoms specific to iron deficiency anaemia?
Pica describes dietary cravings for abnormal things such as dirt and can signify iron deficiency
Hair loss can indicate iron deficiency anaemia
angular stomitis
glossitis and taste disturbance
brittle nails
Koilonychia - spoon shaped nails (late sign of severe iron deficiency anaemia)
what are some general signs of anaemia?
pale skin
conjunctival pallor
tachycardia
raised respiratory rate
what are some signs of specific causes of anaemia?
Koilonychia is spoon shaped nails and can indicate iron deficiency
Angular stomitis can indicate iron deficiency
Atrophic glossitis is a smooth tongue due to atrophy of the papillae and can indicate iron deficiency
Brittle hair and nails can indicate iron deficiency
Jaundice occurs in haemolytic anaemia
Bone deformities occur in thalassaemia
Oedema, hypertension and excoriations on the skin can indicate chronic kidney disease
what investigations should you perform for anaemia?
Haemoglobin MCV B12 folate ferritin blood film
you may consider:
OGD and colonoscopy or bone marrow biopsy if there is unclear causes
what can cause macrocytosis?
> It is commonly an artefact of the testing process – particularly if the sample has been left a long time before being processed
It is also seen in hyperglycaemia
in megaloblastic anaemia, maturation of the nucleus is delayed, which causes larger RBCs
in liver disease there is accumulation of cholesterol and/or phospholipids on the cell surface which leads to larger than normal cells
what can cause VB12 deficiency?
> Insufficient dietary intake
Vegetarianism / vegansim
Malabsorption (Pernicious anaemia – accounts for 50% of cases of B12 deficiency Or lack of intrinsic factor after gastric surgery, Coeliac disease (particularly of the terminal ileum)
HIV
what can cause folic acid deficiency?
Poor diet Alcoholism Coeliac disease Inflammatory bowel disease Medication (Methotrexate, Trimethoprim, Phenytoin - Drug causes tend to only be apparent if there is a prolonged course and / or a high dose
what investigations should you perform for B12 deficiency?
- FBC (raised MCV, low haematocrit)
- Blood smear (megalocytes, hyper-segmented polymorphonucleated cells)
- Serum VB12
- reticulocyte count - low corrected reticulocyte count
- methylmalonic acid (MMA) and homocysteine - markers of VB12 tissue deficiency - will be elevated
- Intrinsic factor antibody - positive if pernicious anaemia is the cause
- antiparietal cell antibody - positive result may suggest pernicious anaemia (however this alone is not sufficient diagnosis as APC antibody may be raised in atrophic gastritis)
how is VB12 deficiency treated?
Vitamin B12 IM injections once every three months (cyanocobalamin or hydroxocobalamin)
how does vitamin B12 deficiency present?
typically presents a megaloblastic anaemia but can also present with peripheral neuropathy and neuropsychiatric complaints
how does folate deficiency usually present?
folate deficiency classically presents as a megaloblastic anaemia with the absence of neurological signs
what investigations would you perform for folate deficiency?
peripheral blood smear (macrocytic anaemia hyper-segmented neutrophils)
FBC - low Hb, elevated MCV and MCH
reticulocyte count - low
serum folate
red blood cell folate - low
serum LDH and serum unconjugated bilirubin - elevated - a sign of ineffective erythropoiesis - present in advanced anaemia
what causes pernicious anaemia?
autoimmune disease caused by antibodies to gastric parietal cells or intrinsic factor
Intrinsic factor is normally secreted by the gastric parietal cells and absorbed in the terminal ileum
B12 binds to intrinsic factor and is absorbed with it
B12 is a coenzyme that produces methionine from homocysteine – which converts folic acid into its active form
So, whenever B12 is deficient, folic acid cannot be utilised
how is folate deficiency managed?
oral folic acid
what should you do if folic acid and B12 deficiency occur together?
The B12 deficiency MUST be treated first or you can aggravate the B12 deficiency and risk causing degeneration of the spinal cord
what is the most common cause of anaemia?
iron deficiency
what can cause iron deficiency anaemia ?
malabsorption (dietary deficiency, coeliac disease, post-gastrectomy
Drugs (PPI, tetracyclines)
Blood loss - often occult blood loss (not seen) - e.g - NSAIDs causing GI blood loss, peptic ulcer disease, malignancy, oesophageal varacies, haemorrhois
Increased physiological requirements - pregnancy, infancy
what investigations should you perform for iron deficiency anaemia ?
FBC
Hb and Haematocrit - low
MCV - low
MCH - mean cell Hb mass per cell - low
MCHC - mean cell Hb concentration per cell - low
red cell distribution width - it is the coefficient of variation in RBC volume - will be greater than 14.6%
Blood smear - microcytic, hypochromic pencil red cells
reticulocyte count will be low and the bone marrow does not have sufficient iron to produce red cells
serum iron - decreased
total iron-binding capacity (TIBC) - increased
transferrin saturation - low
serum ferritin - low
coeliac serology is recommended
H-pylori testing
how is iron deficiency anaemia managed?
oral iron replacement - ferrous sulphate or ferrous gluconate
if symptomatic with cardiac compromise - red cell transfusion
what are causes of haemolytic anaemia?
Hereditary causes - can be subdivided into membrane, metabolism or Hb defects
- Membrane: hereditary spherocytosis
- metabolism: G6PD deficiency
- haemoglobinopathies: sickle cell, thalassaemia
Acquired haemolytic anaemia - can be subdivided into immune and non-immune causes
- Immune causes - autoimmune (warm/cold antibody type), alloimmune (transfusion reaction, haemolytic disease newborn), Drug (methyldopa, penicillin)
- Non-immune causes - microangiopathic haemolytic anaemia (MAHA), prosthetic cardiac valves, paroxysmal nocturnal haemoglobinuria, infectious - malaria, drug - dapsone
what is haemolytic anaemia?
it encompasses a number of conditions that result in the premature destruction of RBCs.
what are the symptoms of haemolytic anaemia?
pallor jaundice fatigue SOB dizziness splenomegaly
what investigations would you perform for haemolytic anaemia?
FBC
MCHC - mean haemoglobin concentration per cell - increased - may indicate presence of spherocytes and reticulocytes
reticulocyte count - increased - indicates appropriate bone marrow response to anaemia
peripheral blood smear - abnormal forms
unconjugated bilirubin may be elevated due to increased haem catabolism
High LDH and low haptoglobin is 90% specific to haemolytic anaemia
Urinalysis - haemoglobinuria is present in intravascular haemolysis
Direct antiglobulin test (coombs test) - identifies RBCs coated with antibody/compliment and a positive test usually indicates and immune cause
how is autoimmune haemolytic anaemia managed?
corticosteroids - prednisolone or dexamethasone
supportive care includes folic acid supplement
how is autoimmune haemolytic anaemia diagnosed?
Coombs test
if coombs test is negative it would suggest an aquired cause of haemolytic anaemia
how is autoimmune haemolytic anaemia catagorised?
Warm or cold according to what temperature the antibodies best cause haemolysis
Warm AIHA - the antibody (usually IgG) causes haemolysis best ay body temp and haemolysis tends to occur in extravascular sites (e.g. spleen).
Management options include steroids, immunosuppression, splenectomy
causes: AI disease (SLE), neoplasia (lymphoma, CLL), drugs (methyldopa)
Cold AIHA - usually IgM and causes best haemolysis and 4 degrees C. Haemolysis is mediated by complement and is more commonly intravascular. Features may include symptoms of raynaud’s and acrocyanosis.
Patients respond well to steroids
Causes: neoplasia (lymphoma), infectious (mycoplasma, EBV)
what is sideroblastic anaemia?
it is a condition where red cells fail to completely form haem, whose biosynthesis take place partly in the mitochondria. This leads to deposits of iron in the mitochondria that form a ring around the nucleus call a ring sideroblast.
It may be congenital or acquired.
*** always think of sideroblastic anaemia when there is a microcytic anaemia that is not responding to iron
what are the different causes of sideroblastic anaemia?
congenital cause: delta aminolevulinate synthase-2 deficiency
acquired causes:
- myelodysplasia
- alcohol
- lead
- anti TB meds
what would investigations show in sideroblastic anaemia?
hypochromic microcytic anaemia
bone marrow will show sideroblasts and increased iron stores
how is sideroblastic anaemia managed?
treat underlying cause
supportive management
pyridoxine may help
what are the features of fanconi anaemia?
AR
aplastic anaemia increased risk of AML short stature thumb/radius abnormalities cafe au lait spots
what is aplastic anaemia ?
it is defined by pancytopenia with hypocellular bone marrow and no abnormal cells.
what are some causes of aplastic anaemia?
most often idiopathic
drug exposure: chloramphenicol, NSAIDS, gold therapy, benzene - however the lag time between exposure and disease presentation is usually several weeks to months
Viral - hepatitis and other viral illness
inherited bone marrow failure syndromes - fanconi anaemia, dyskeratosis congenita, shwachman-diamond syndrome, GATA2 deficiency
what are the features of aplastic anaemia?
normochromic, normocytic anaemia
leukopenia with lymphocytes relatively spared
thrombocytopenia
may be the presenting feature of ALL or AML
a minority of patients later develop paroxysmal nocturnal haemoglobinuria or myelodysplasia
increased likelyhood of infection bleeding bruising bleeding gums epistaxis mouth infections are common
what investigations would you perform for aplastic anaemia?
FBC - pancytopenia is common
Reticulocyte count - a low reticulocyte count identifies anaemia as being hyp-oproductive
bone marrow biopsy and cytogenic analyses - hypo-cellular marrow with nor abnormal cell population
HIV test ing
LFTS
how is aplastic anaemia managed?
treat causes
immunosupressive therapy - antithymocyte immunoglobulin and methylprednisolone and ciclosporin
if severe disease - stem cell transplant
what is hereditary spherocytosis?
an inherited abnormality caused by defects in structural membrane proteins.
it causes a haemolytic anaemia and the severity of the haemolysis is related to the type and amount of membrane disruption
what are the clinical features of hereditary spherocytosis?
pallor
jaundice
splenomegaly
fatigue
what investigations would you perform for hereditary spherocytosis:?
FBC - can be variable depending on the severity of HS
reticulocyte count - elevated
blood smear - spherocytes present, may also demonstrate pincer cells
serum bilirubin - elevated
direct anti-globulin test to rule out auto-immune haemolysis
how is hereditary spherocytosis managed?
supportive care with RBC transfusions
folic acid supplementation
what is sickle cell anaemia?
it is an AR condition thats results in synthesis of abnormal Hb chain termed HbSS.
people may just have sickle cell trait (HbAS - usually no symptoms unless exposed to extreme hypoxia)
HbSC - milder course than HbSS but there is increased risk on thrombosis
when does sickle cell anaemia present?
it doesnt usually present until 4-6 months when the abnormal HbSS molecules take over from fetal Hb
it causes a single gene defect in the beta chain of Hb
what is the pathophysiology of sickle cell disease?
Polymerisation of sickle Hb in RBC can be triggered by hypoxia and acidosis which causes cells to become rigid and deform into a sickle (crescent shape).
These deformed shapes may cause vaso-occlusion in the small vessels or adhere to vascular endothelium, resulting in larger vessels and slowing blood flow.
The deformed cells are also prone to haemolysis which contribute to anaemia.
what is though to precipitate vaso-occlusive episodes?
acidosis dehydration cold temperatures extreme exercise stress infections
why are people with sickle cell anaemia at risk of thrombosis and pulmonary hypertension?
Because long standing intravascular haemolytic anaemia results in nitrous oxide deficiency
Nitrous oxide deficiency can cause thrombosis as well as pulmonary vasoconstriction and endothelial dysfunction which can lead to pulmonary hypertension
what are the clinical features of sickle cell anaemia?
persistent pain in skeleton, chest and/or abdomen
dactylitis - swollen dorsa of hand and feet
mild anaemia - usually no symptoms due to hyperdynamic circulation and a lower oxygen affinity of HbS than normal Hb
jaundice
sickle cell crisis
how does a vaso-occlusive crisis present in SC anaemia ?
aka - painful crisis symptoms are typically: - pain - fever - it can cause priapism in men by trapping blood in the penis causing a painful and persistent erection - this is a urological emergency and treated with aspiration of blod from the penis
what is splenic sequestration crisis in SC anaemia?
is is caused by RBC blocking blood flow within the spleen
this causes an acutely enlarged and painful spleen
The pooling of the blood in the spleen can lead to severe anaemia and circulatory collapse
it is considered and emergency
management is with blood transfusions and fluid resuscitation
splenectomy prevents it happening and is often performed in cases of recurrent crisis
what is acute chest syndrome in SC anaemia?
a diagnosis of acute chest syndrome requires:
- fever or respiratory symptoms with new infiltrates seen on chest XR
it can be due to infection (e.g. pneumonia or bronchiolitis) or non infective causes (pulmonary vas-occlusive or fat emboli)
this is medical emergency with high mortality and requires prompt management and treatment of underlying condition:
- antibiotics or antivirals for infection
- blood transfusions for anaemia
- incentive spirometry - using a machine that encourages effective and deep breathing
- artificial ventilation
what are the complications of sickle cell disease?
anaemia increased risk of infection stroke avascular necrosis pulmonary hypertension priapism CKD sickle cell crises acute chest syndrome
what investigations would you perform for sickle cell disease?
it is tested for on the new born screening heel prick test at 5 days of age
DNA based assays
peripheral blood smear - presence of red blood cells, sickle shaped cell and howell-jolly bodies
FBC and reticulocyte count
how is sickle cell disease managed?
VASO-OCCLUSIVE CRISUS
- analgesia
- supportive care - oxygen, rehydration
- correction of cause
- consider antibiotics if there is evidence of infection
- blood transfusion
ACUTE CHEST SYNDROME
- oxygen and incentive spirometry
- analgesia
- broad spectrum antibiotics
ONGOING
- supportive care and management of complications (early diagnosis, pneumococcal immunisation, antibiotic prophylaxis)
- hydroxycarbamine can be considered in patients aged >2 years
- bone marrow transplant can be considered in children with severe complications of sickle cell anaemia
what is thalassaemia?
thalassaemia is an AR inherited disorder of the production of alpha or beta globin chains of Hb
Normal Hb contains 2 alpha and 2 beta globin chains.
will usually present with a microcytic hypochromic anaemia which will not respond to iron
where are the genes coding for alpha and beta globin chains found?
alpha - chromosome 16
beta - chromosome 11
what are the four distinct types of alpha thalassaemia?
> silent carrier - 1 affected alpha globin gene
alpha thalassaemia trait - 2 affected alpha-globin genes (microcytosis with or without mild anaemia)
HbH disease - typically 3 affected alpha-globin genes (moderate anaemia and splenomegaly)
Hb Bart Hydrops fetalis syndrome (typically deletion of all 4 alpha-globin genes (incompatible with life - infants are still born or die shortly after birt)
as a result there are decreased alpha chains and increased beta chains
the severity of the clinical manifestations of anaemia and haemolysis correspond with the genetic defect and the degree of impairment in alpha-globin synthesis
what investigations would you order for alpha thalassaemia?
peripheral blood smear - hypochromic microcytic anaemia (MCV - low, MCH - low)
RBC count - increased
reticulocyte count - raised
how is alpha thalassaemia managed?
regular (2-4 week) life long red blood cell transfusion
folic acid supplementation
iron chelation therapy (oral deferasirox or SC desferrioxamine)
splenectomy if hypersplenism persists
what is beta thalassaemia?
an inherited microcytic anaemia caused by mutations of the beta-globin gene leading to decreased or absent synthesis of beta-globin resulting in ineffective erythropoiesis.
the reduction in beta chains results in excess alpha chains - this results in RBC precursor destruction in bone marrow and spleen resulting in proliferation of marrow, boney deformity (mongoloid faces, bossing of skull, thinning of long bones) and progressive splenomegaly)
what are the different phenotypic classifications of beta-thalassaemia?
> Silent carrier: completely asymptomatic with normal haematological parameters.
Beta-thalassaemia minor (commonly referred to as beta-thalassaemia trait): usually asymptomatic
Beta-thalassaemia intermedia: usually a similar presentation to beta-thalassaemia major but as a toddler or older child; symptoms are usually less pronounced and the course is usually more insidious.
Beta-thalassaemia major (also called Cooley’s anaemia): often presents at a few months of age with progressive pallor and abdominal distension; perinatal history is most often uneventful, and the infant may be pale, possibly with poor feeding and decreased activity; hepatosplenomegaly and bony abnormalities are often present at presentation, most often of the skull (frontal and parietal bossing, and chipmunk facies).
how is beta-thalassaemia diagnosed?
> FBC - microcytic anaemia
peripheral blood smear - microcytic red cells, tear drops, microspherocytes, large number of nucleated red cells
reticulocyte - elevated
haemoglobin electrophoresis is used to diagnose globin abnormalities
genetic testing
X-ray - skull - hair on end deformity, Maxilla - overbite and overgrowth
what is a complication of regular blood transfusions?
there is progressive increase in the body iron load which gets deposited in liver and spleen resulting in fibrosis and cirrhosis
deposition in endocrine glands and heart results in diabetes, hypothyroidism and premature death
how is beta-thalassaemia managed?
if they just have trait - offer genetic counselling and iron supplement avoidance unless they have iron deficiency
Regular transfusion s
Iron monitoring and chelation - oral deferasirox or SC desferrioxamine
they may require splenectomy
folate supplements
ascorbic acid can increase iron output in urine
what is G6PD deficiency ?
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the commonest red blood cell enzyme defect.
G6PD is essential to protect RBCs from oxidative stress so in results in RBCs lifespan hen there is oxidative damage - leading to a haemolytic anaemia (leads to an intravascular haemolysis)
It is X-linked so common in men
It affects people particularly in mediterranean, Africa, and asian populaitons
what are the features of G6PD deficiency ?
neonatal jaundice is often seen intravascular haemolysis gallstones are common splenomegaly may be present Heinz bodies on blood films. Bite and blister cells may also be seen
how does G6PD deficiency present?
It is usually asymptomatic but will get an oxidative stress crisis which can be precipitated by:
- Drugs: antimalarials (primaquine), antibiotics (ciprofloxacin, nitrofurantoin), sulph - group drugs (sulphonamides, sulphasalazine, sulfonylureas)
- infections
- broad/fava beans
during an attack there will be rapid anaemia and jaundice
will often present as neonatal jaundice
how is G6PD deficiency diagnosed?
FBC - will be normal between attacks
> during an attack - there will be anaemia, and normochromic red cell index
Blood smear - the presence of blister or bite cells suggests oxidative stress as a cause of haemolysis, heinz bodies are seen in acute haemolysis
Reticulocyte count will be increased
Urinalysis - will detect urobilinogen and protein if intravascular haemolysis is present
Unconjugated bilirubin - raised - due to increased haem metabolism
LDH - riased due to RBC destruction and Hb release
G6PD fluorescent test - negative
G6PD spectrophotometry - reduced G6PD activity
How is G6PD deficiency managed?
stop drugs and avoid precipitating factors
folic acid
supportive care
blood transfusions if severe
what is anaemia of chronic disease?
Anaemia of chronic disease is a common syndrome in which the anaemia is due to inflammation-mediated reduction in RBC production and survival
it can be normocytic or microcytic
may be hypochromic (in Crohn’s and RA)
It occurs as a result of:
- chronic infection (TB)
- chronic inflammation
- autoimmune reactions (Crohn’s, RA, SLE)
- malignancy
- CKD
this condition can result in release of pro-inflammatory cytokines, often with activation of the reticuloendothelial system. This cytokines trigger changes in intracellular iron metabolism.
Elevated levels of inflammatory cytokines, such as tumour necrosis factor alpha, have been associated with apoptosis of erythroid precursor cells in the bone marrow, which might account for anaemia of chronic disease seen in rheum conditions
the lifespan of RBCs may be shortened by increased erythrophagocytosis by macrophages and damage cytokine-generated free radicals.
how does anaemia of chronic disease presnet?
- systemic symptoms of underlying condition
- decreased exercise tolerance
- SOB with exercise
- Fatigue
- pallor
what investigations would you perform for anaemia of chronic disease?
> FBC - Hb levels (may indicate alternative cause or co-existing cause), WBC (raised may indicate infection), Platelet count (may be raised due to underlying infection or inflammation)
MCV - may be normal or reduced
MCHC - normal or reduced (may be normochromic or hypochromic)
peripheral blood smear
serum ferritin - increased - this is good to distinguish from iron deficiency anaemia as in iron defeciency anaemia the ferritin will fall
absolute reticulocyte count - low for the degree of anaemia - indicative of underproduction by the bone marrow which is typical in anaemia of chronic disease
how is anaemia of chronic disease managed?
- treatment of underlying disease and observation
- if needed red blood cell transfusion
- erythropoiesis-stimulating agents(ESA) - epoetin alfa SC once weekely or darbepoetin alfa SC once every two weeks
- iron supplementation
Giving EPO/ESA is particularly good in renal failure as in this the EPO levels are directly affected.
what are the side effects of giving EPO to patients?
flu like symptoms hypertension increased platelet count increased risk of thromboembolic events hyperkalaemia skin reactions headaches
what is aplastic anaemia?
aplastic anaemia due to bone marrow failure - pancytopenia with hypocellularity of the bone marrow resulting in bone barrow failure
Congenital - Fanconi anaemia
Acquired - chemicals (benzenes), drugs (cytotoxics, chemotherapy, chloramphenicol, carbamazepine gold, insecticides, ironising radiation )
Infection (viral hepatitis, HIV, EBV, TB)
these things lead to a reduction in the number of pluripotent stem cells resulting in bone marrow failure
What is polycythaemia?
It is a raised RBC count with increased cell volume
Relative cause: dehydration, stress (gaisbock syndrome)
Primary causes: polycythaemia vera
Secondary causes: COPD, altitude, obstructive sleep apnoea, excessive EPO
To differentiate between relative and true (primary/secondary) polycythaemia red cell mass studies are used - in true the total red cell mass is higher.
what is polycythaemia vera?
> it belongs to the group of Philadelphia Chromosome-negative myeloproliferative neoplasms
It is a haematological malignancy where there in clonal proliferation of marrow stem cells leading to increase in red cell volume, often accompanied by overproduction of neutrophils and platelets. The raised haematocrit leads to hyper-viscosity and thrombosis
Recently it has been established that a mutation in JAK2 is present in most patients
peaks in the 6th decade
what is haematocrit?
the ratio of the volume of red blood cells to the total volume of blood
How does polycythaemia vera present?
> non specific symptoms/signs: night sweats, pruritus (usually after contact with warm water) , headaches, dizziness, lethargy, tinnitus, gout (secondary to increased red cell turnover), splenomegaly, erthromelalgia, redness of fingers, palms, toes and heels
there may be signs of thrombosis
haemorrhage secondary to abnormal platelet function
hypertension
what investigations would you perform for polycythaemia vera?
- Hb - elevated Hb has good diagnostic sensitivity but poor specificity
- Haematocrit - raised
- WBC - most cases of polycythaemia vera are associated with at least a modest leukocytosis
- platelet count - same as WBC
- MCV - usually low and coexistent with iron deficiency
- JAK2 gene mutation screen
how do you manage polycythaemia vera?
There is no cure - treatment aims to maintain a normal blood count
- Venesection - aims to lower haematocrit to relieve symptoms - removal of 500-500mls of blood weekly.
- if venesection is not tolerated - reduce blood cell production from bone marrow with hydroxycarbamide
- Aspirin to reduce risk of thrombosis
- anti-gout - allopurinol
- survival = 10-20 years - will sometimes progress to AML or myelofibrosis
