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Haematology > Sickle Cell disease > Flashcards

Sickle Cell disease Flashcards

1
Q

Define sickle cell disease?

A

Sickle cell anaemia is caused by an autosomal-recessive single gene defect in the beta chain of haemoglobin, which results in production of sickle cell haemoglobin (HbS).

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2
Q

outline the different genotypes for sickle cell disease?

A
  • sickle cell anaemia = Homozygoes HbSS
  • Sickle cell trait= carrier of one copy of HbS therefore HbAS
  • Sickle cell diseae= includes compound heterozygosity for HbS and :
  • HbC (abnormal haemoglobin in which glutamic acid is replaced by lysine at the 6th position in the beta-globin chain) - HbSC
  • Beta-thalassemia – HbS/Bthal
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3
Q

describe the disease severity of sickle cell trait?

A

Causes no disability (except in hypoxia e.g. anaesthesia, high altitudes and extreme exertion – may cause vaso-occlusive event)

-protects from falciparum malaria

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4
Q

what is HbC?

A

Abnormal haemoglobin in which glutamic acid is replaced by lysine at the 6th position in the beta-globin chain

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5
Q

what are the factors that precipitate sickling?

A

IHAD

infection

hypoxia

acidosis

dehydration

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6
Q

outline the aetiology of sickle cell disease?

A

Autosomal recessive

Point mutation in the beta-globin generesulting in the substitution of glutamic acid in position 6 by valine (non-polar so insoluble)-> results in formation of abnormal HbS

Deoxygenationof HbS alters the conformation resulting in sicklingof red cells – can polymerize and form fibres known as tactoids

Sickling makes the red cells more fragile and inflexible

Once dehydrated the sickled cells adhere to the vasc endo more(particularly the post-capillary venules)

These sickled red cells are prone to:

Sequestration and destruction (reduced red cell survival ~ 20 days)

Occlusion of small blood vessels causing hypoxia, which leads to further sickling and occlusion

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7
Q

what is the point mutation in sickle cell disease?

A

point mutation in the beta-globin gene resulting in the substitution of glutamic acid in position 6 by valine (non-polar so insoluble)

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8
Q

summarise the epidemiology of sickle cell disease?

A

Rarely presents before 4-6 months (because HbF can compensate for the defect in adult haemoglobin)

Common in Africa, Caribbean, Middle-Eastand other areas with a high prevalence of malaria

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9
Q

what are the presenting symptoms of sickle cell disease?

A
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10
Q

what are the signs of sickle cell disease on physical examination?

A

Signs secondary to VASO-OCCLUSION, ISCHAEMIA or INFARCTION

  • Bone - joint or muscle tenderness or swelling (due to avascular necrosis)
  • Short digits - due to infarction in small bones of the hands

Retina - cotton wool spots due to retinal ischaemia

Jaundice – indication of haemolysis

Signs secondary to SEQUESTRATION CRISES

Signs of anaemia

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11
Q

what are the signs secondary to sequestrian crises?

A

Organomegaly

  • spleen is enlarged in early disease
  • later on spleen will reduce in size due to splenic atrophy

Priapism

  • Microvascular occlusion of the penis so blood can’t leave and it remains painful and erected for a long time
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12
Q

what are the symptoms of sickle cell disease secondary to vaso-occlusion or infarction?

A

Autosplenectomy ( splenic atrophy or infarction) - leads to increased risk of infections with encapsulated organisms ( eg pneumococcus meningococcus)

Abdominal pain - due to messenteric ischaemia

Bones

  • Painful crises affect small bones of the hands and feet causing dactylitis in CHILDREN
  • Painful crises mainly affect the ribs, spine, pelvis and long bones in ADULTS
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13
Q

which bones are affected in painful crises in children?

A

small bones of hands and feet- cause dactylitis in children

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14
Q

which bones are mainly affected in painful crises in adults?

A

ribs, spine, pelvis and long bones

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15
Q

what are the symptoms of avascular necrosis in sickle cell disease?

A

Myalgia and Arthralgia

Leg ulcers

Low flow priapism

CNS

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16
Q

what are the symptoms of sickle cell disease that affect the lungs?

A

ACUTE CHEST SYNDROME

  • breathlessness
  • cough
  • fever
  • pain
17
Q

what are the appropriate investigations for sickle cell disease?

A

bloods

blood film

sickle solubility test

Haemoglobin electrophoresis= DEFINITIVE

Hip X ray

18
Q

Describe blood results in sickle cell disease?

A

FBC

  • Leukocytosis is a presentation in infants
  • Low Hb
  • Reticulocytes: HIGH - in haemolytic crises, LOW - in aplastic crises

U&Es

19
Q

describe blood film in sickle cell disease?

A

sickle cells

anisocytosis ( variation in size of red cells)
Features of hyposplenism

  • Target cells
  • Howel-Jolly bodies
20
Q

what are the results for the sickle cell solubility test?

A

Shows HbS

Absence of HbA (if homozygous HbS)

High HbF

21
Q

What may be seen on the hip x ray in sickle cell disease?

A

Femoral neck is a common place for avascular necrosis

22
Q

What investigations should you consider for sickle cell disease?

A

MRI or CT Head - If there are neurological complications

Plain X-rays of long bones – to confirm presence of bone infarction

Bacterial cultures – to confirm infection (can cause sickle cell crisis)

CXR – if resp symptoms present

23
Q

How do you manage an acute ( painful crises) for sickle cell disease?

A

Oxygen

IV Fluids – V IMPORTANT

Strong analgesia(IV opiates – codeine or morphine(children))

  • Can also give subcut analgesia
  • Many cause pruritus which should be managed with diphenhydramine (anti-histamines)
  • PCA – Patient controlled analgesia

Antibiotics

Cross match blood

Give transfusion if Hb or reticulocytes fall sharply

24
Q

outline the management for sickle cell disease?

A

ACUTE (PAINFUL CRISES)

  • Oxygen
  • IV Fluids – V IMPORTANT
  • Strong analgesia (IV opiates – codeine or morphine(children))
  • Antibiotics
  • Cross match blood
  • Give transfusion if Hb or reticulocytes fall sharply

Infection Prophylaxis– as splenic infarction leads to hyposplenism

  • Penicillin V
  • Regular vaccinations (particularly against capsulated bacteria e.g. pneumococcus)

Folic Acid-If severe haemolysis or in pregnancy

Hydroxyurea/Hydroxycarbamide– if frequent crises

  • Increases HbF levels
  • Reduces the frequency and duration of sickle cell crisis
  • Most common complication is neutropenia and hepatic/renal impairment
  • Contraindicated in BM suppressive disorders e.g. leukopenia and thrombocytopenia
  • For patients who are intolerant ro hydroxycarbamide, L-glutamine can be given but this should be avoided in patients with renal or hepatic impairment

Red Cell Transfusion

  • For SEVERE anaemia
  • Repeated transfusions (with iron chelators) may be required in patients suffering from repeated crises

Advice

  • Avoid precipitating factors, good hygiene and nutrition, genetic counselling, prenatal screening

Surgical

  • Bone marrow transplantation – may be curative
  • Joint replacement in cases with avascular necrosis

Febrile children may risk septicaemia – repeated admission can be avoided with ceftriaxone (AB)

25
Q

what are the possible complications of sickle cell disease?

A

Aplastic crises

  • Infection with Parvovirus B19 can lead to a temporary cessation of erythropoiesis (which can cause red cell count to plummet in sickle cell patients because their red cells have a shortened life span and can’t tolerate a cessation of erythropoiesis)

Cholelithiasis and liver complications

Infection

Leg ulcers

Lung damage

Opioid dependence

Poor growth in children

Chronic renal failure

Haemolytic crises

Pigment gallstones

Retinal disease

Renal papillary necrosis

Cardiomyopathy

Iron overload from repeated transfusion - Treat with desafirox (oral) as venesection in pts with SCA is almost impossible and pt is anaemic!!!

26
Q

what is the cause of aplastic crises in patients with sickle cell disease?

A

Infection with Parvovirus B19 can lead to a temporary cessation of erythropoiesis (which can cause red cell count to plummet in sickle cell patients because their red cells have a shortened life span and can’t tolerate a cessation of erythropoiesis)

27
Q

summarise the prognosis of patients with sickle cell disease?

A

Most patients with sickle cell disease who manage their disease well will survive until around the age of 50 yrs

Mortality is usually the result of:

  • Pulmonary or neurological complications in ADULTS
  • Infection in CHILDREN

Haematology (23 decks)

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