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Yr 3 Haem > sickle cell disease > Flashcards

sickle cell disease Flashcards

1
Q

definition of sickle cell disease

A

Includes compound heterozygosity for Hb S and C and for Hb S and b-thalassaemia.

sickle cell anaemia - a chronic condition with sickling of RBC caused by inheritence of HbS

sickle cell anaemia - homozygosity for HbS (SS)

sickle cell trait - carries one copy of HbS (AS) - no disability, protective from falciparum malaria. May get some sx in hypoxia - in plane or anaesthesia - need pre-op sickle test

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2
Q

pathology of sickle cell disease

A

Autosomally recessive inherited point mutation in the b-globin gene = valine substituting glutamic acid on position 6 = HbS rather than HbA

(HbA2 adn HbF are still produced)

deoxygenation of HbS alters conformation with the resulting hydrophobic interactions between adjacent HbS and formation of insoluble polymers = sickling of red cells with increased fragility (so haemolyse) and inflexibility = vaso-occulsive crisis

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3
Q

what are sickled cells prone to doing

A

sequestation and obstruction = reduced red cell survival ie 20days

occlusion in small bv = hypoxia = further sickling and occlusion

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4
Q

precipitating factors for sickling

A

infection

dehydration

hypoxia

acidosis

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5
Q

epidemiology of sickle cell disease

A

rarely presents before 4–6 months (because of continuous production of foetal haemoglobin).

Common in Africa, Caribbean, Middle East and areas with high prevalence of malaria (carrier frequency in Afro-Caribbeans 8%).

1:700 people of African descent.

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6
Q

what are the sx of sickle cell disease

A

they are secondary to vaso-occlusion or infarction:

  • Autosplenectomy (splenic atrophy or infarction) = increased infection risk with encapsulated organisms - (e.g. pneumococcus, Haemophilus influenzae, meningococcus, Salmonella).
  • abdo pain
  • bone involvement
  • myalgia and arthralgia
  • CNS - fits and strokes eg hemiplegia
  • retina - visual loss (proliferative retinopathy)
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7
Q

bone sx of sickle cell disease

A

painful crisis affecting small bones in hands and feet (dactylitis) in children, and ribs, spine, pelvis and long bones in adults

chronic hip and shoulder pain - avascular necrosis

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8
Q

sx of sequestration crisis in sickle cell disease

A

this is where red cells pool in various organs

  • spleen
  • liver = exacerbation of anaemia
  • lungs = Acute chest syndrome: breathlessness, cough, pain, fever
  • corpora cavernosa = persistent erection (pripiasm) and impotence
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9
Q

signs of sickle secondary to vaso-occlusion, ischemia or infarction

A

bone, joint or muscle tenderness or swelling caused by avascular necrosis

short digits from infarction in small bones

retina - cotton wool spots from areas of ischemic retina

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10
Q

signs of sickle cell disease secondary to sequestation crisis

A

organomegaly - spleen in early disease, but later decreases in size because of splenic atrophy

priapism

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11
Q

general signs of sickle

A

signs of anaemia

secondary to vaso-occlusion, ischemia, infarction

secondary to sequestration crisis

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12
Q

Ix for sickle cell disease

A

blood

blood film

sickle solubility test

haemoglobin electrophoresis

Hip XR - common site for avascular necrosis of femoral head

MRI or CT head - neuro complications

aim for dx at birth to allow for infection prophylaxis early

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13
Q

blood results for SCD

A

FBC

  • anaemia 60-90g/L
  • reticulocytes are high in haemolytic crisis and low in aplastic crisis
  • high BR

UE

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14
Q

blood film in SCD

A

sickle cell

anisocytosis

features of hyposplenism - target cells, Howell-jolly bodies

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15
Q

sickle solubility test

A

dithionate added to blood = increased turbidity

doesnt distinguish between SS and AS

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16
Q

Hb electrophoresis for SCD

A

confirms dx

HbS, absence of HbA in HbSS and increased levels of HbF

17
Q

management for acute painful crisis of SCD

A

oxygen

IV fluids

strong analgesia - IV opiates

AB

crossmatch blood, check FBC, and reticulocytes

septic screen - blood cultres, MSU +- CXR if high temp or chest signs

keep warm

measure PVC, reticulocytes, liver and spleen size twice daily

transfusion if Hb or reticulocytes fall sharply - helps oxygenation, as good as exchange transfusion

exchange transfusion reserved for people who are rapidly worsening

18
Q

Mx of SCD

A

infection prophylaxis

  • penicillin V.
  • Regular vaccinations (e.g. against pneumococcus)

early rescue out pt AB to prevent admissions ge ceftriaxone. Consider admission if: Hb 30 ≈ 109 /L, T° >40°C, severe pain, dehydration, lung infiltration.

folic acid - in severe haemolysis or in pregnancy

hydroxyurea - increase HbF levels and reduces frequency and duration of sickle cell crisis

exchange transfusion - in severe crisis, before surgery, pregnancy

surgical

19
Q

surgical Mx of SCD

A

bone marrow transplant in selected pts

joint replacement for avascular necrosis

20
Q

advice given to SCD

A

avoid precipitating factors

good hygiene and nutrition

genetic counselling

prenatal screening

21
Q

complications of SCD

A

complications of vaso-occluision and sequestration

splenic infarction before 2yrs due to microvascular occlusion = infection - aplastic crises - infection with B19 parvovirus, temporary cessation of erythropoiesis

haemolytic crisis

pigment gallstones

cholecystitis

renal papillary necrosis

leg ulcers - local ischemia

cardiomyopathy

poor growth

retinal disease

iron overload

lung damage: hypoxia -> fibrosis -> pul HTN

22
Q

prognosis of SCD

A

most, with good care, survive to 50yrs

Major mortality is usually a result of pulmonary or neurological complications (adults) or infection (children).

23
Q

vaso-occlusive crisis in SCD

A

common - due to microvascular occlusion

affects the marrow = severe pain

triggered by precipitants

hands and feet affected if <3yr = dactylitis

occlusion may = mesenteric ischemia - mimicking acute abdo

CNS infarction -> stroke, seizure or cognitive defetc

Transcranial doppler US indicates stroke risk - blood transfusions prevent by reducing HbS

avascular necrosis

leg ulcers

low flow priapism

24
Q

priapism in SCD

A

from vaso-occlusive crisis

also seen in CML

may respond to hydration, a-agonists eh phenylephrine, or aspiration of blood +irrigation with saline

if for >12hr - prompt cavernosus-spongiosum shunting can prevent later impotence

25
Q

Aplastic crisis in SCD

A

due to parvovirus 19

sudden reduction in marrow production, especially RBCs

self limiting <2wks

transfusion may be needed

26
Q

sequestation crisis in SCD

A

mainly affects children, in adults the spleen becomes atrophic

pooling of blood in spleen +- liver = organomegaly, severe anaemia and shock

urgent transfusion needed

27
Q

prevention of SCD

A

genetic counselling

prenatal tests

parental education prevent deaths from sequestation crisis

28
Q

exchange transfusion for SCD

A
  • blood is removed, and donor blood is given in stages.

indictations:

  • severe chest crisis
  • suspected CNS event
  • multiorgan failure

when the proportion of HbS should be reduced to <30%

inform their haematologist of admission early

29
Q

acute chest syndrome in sickle cell disease

A

entails pulmonary infiltrayes involving complete lung segments = pain, fever, tachypnoea, wheeze and cough

serious

prodromal painful crisis occur 2.5 days before abnormalities on CXR for 50% pts

causes of infiltrates are fat embolism from marrow or infection with chlamydia, mycoplama or virus

30
Q

management of SCD acute chest syndrome

A

oxygen

analgesia

empirical AB - cephalosporin + macrolide until culture results

bronchodilators eg salbutamol - if wheexing or have obstructive pul function

blood transfusion (exchange if severe)

ITU of PaO2 cannot be kept above 9.2kPa (70mmHg) when breathing air

31
Q

patient controlled analgesia in SCD

A

good option if supportive measures and oral analgesia dont control the pain

pt give bolus when needed

check RR and GCS and sats

Yr 3 Haem (16 decks)

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