Haem Flashcards
Define antiphospholipid syndrome
Characterized by the presence of antiphospholipid antibodies (APL) in the plasma, venous and arterial thromboses, recurrent foetal loss and thrombocytopenia.
Explain the aetiology / risk factors of antiphospholipid
syndrome
Difference between primary and secondary
Which individuals are susceptible
What is the genetic and environmental factors leading to the disease
What is the name of the main antiphospholipid antibody?
What is the effect of this antibody
Name another anti-phospholipid antibody
What other condition are these antibodies present in, and what is the implication of this?
What leads to -clotting -thrombocytopenia -anaemia in APS
AUTOIMMUNE
Antiphosholipid antibodies attack phosphilipids in the cell membrane, or plasma proteins bound to those anionic phospholipids.
Primary=happens by itself
Secondary=occurs with other AI diseases
APL may develop in susceptible individuals (e.g. those with rheumatic diseases e.g. SLE) following exposure to infectious agent –> secondary APS
Associated with mutated HLA-DR7 gene, allows production of APL antibodies
Once APL antibodies are present, second hit needed for development of syndrome (an environmental trigger)
Environmental triggers:
- Infections (syphilis, HIV, hep C, malaira)
- Drugs (CVS: procainamide, quiniine, propanalol, hydralazine; antipsychotics: phenytoin, chlorpromazine)
Main antiphospholipid antibody anti-beta2-glycoprotein I
This antibody targets anti-beta2-glcoprtein I, aka Apolipoprotein H. This lipoprotein usually inhibits agglutination
The procoagulant actions of APL is explained by their effect on b2 glycoprotein-I (clotting and platelet aggregation inhibitor), protein C, annexin V, platelets and fibrinolysis.
(remember that one of the key features of APS is arterial and venous thromboses)
Another anti-phospholipid antibody is anti-cardiolipin which targets the cardiolipin phospholipid in the inner mitochondrial membrane. This Ab is also present in syphilis, so having APS may lead to a false positive result for syphilis
See above for clotting, but autoantibodies targeting platelets and RBCs leads to thrombocytopenia and anaemia respectively.
Complement activation critical for pregnancy complications
Summarise the epidemiology of antiphospholipid syndrome
More common in young women
Accounts for 20% of strokes in < 45-yearolds and 27% of women with > 2 miscarriages.
Recognise the presenting symptoms of antiphospholipid syndrome
What is catastrophic antiphospholipid syndrome
Recurrent miscarriages (due to thrombosis leading to placental infarction),
history of arterial thromboses (stroke),
venous thromboses (DVT, pulmonary embolism),
renal failure (due to small capillaries, and the effects of clots here)
headaches (migraine),
chorea,
epilepsy
catastrophic antiphospholipid syndrome= rapid organ failure due to generalised thrombosis
Recognise the signs of antiphospholipid syndrome on physical examination
typical skin finding?
Livedo reticularis (swelling of venules due to obstructing clot).. appears as a mottled, purplish discolouration of skin
Signs of SLE (malar flush, discoid lesions, photosensitivity).
Signs of valvular heart disease (libman sachs endocarditis, see card below!)
Identify appropriate investigations for antiphospholipid syndrome and interpret the results
Diagnosis requires 1 clinical and 1 lab diagnosis criteria
Clinical criteria: 1. Hx thrombosis 2. Pregnancy complications
FBC (reduced platelets), ESR (usually normal), U&Es (APL nephropathy), clotting screen (raised APTT).
Presence of APL may be demonstrated by:
- ELISA testing for anticardiolipin and antib 2-GPI antibodies.
- Lupus anticoagulant assays: Clotting assays showing effects of APL on the phospholipiddependent factors in the coagulation cascade.
False-positive VDRL test for syphilis may be a clue to the presence of any type of APL.
Define haemolytic uraemic syndrome
Characterised by triad of:
- Microangiopathic haemolytic anaemia (it is one of the 3 causes, the other 2 are TTP and DIC)
- Thrombocytopenia
- Acute renal failure
The condition is categorised by whether it is associated with diarrhoea (D+, typical) or not (D-, atypical)
Epidemiology of HUS
Mainly children < 5 years of age
What causes haemolytic syndrome
1) Bacterial infection with E Coli O157:H7 (due to shiga like toxin), or shigella. This initially causes bloody diarrhoea too (D+). Infected from outbreaks after eating uncooked contaminated meat.
2) D negative form include pneumococcal lung infection, drugs (ciclosporin, some chemo agents), bone marrow transplant and pregnancy
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How does bacterial infection cause haemolytic uraemic syndrome
E Coli O157:H7 or shigella bind to intestinal wall and are picked up by white cells.
The kidneys have Gb3 receptor which picks up the antigens on the white blood cell. This causes death of the endothelial cells in the renal vasculature.
These dead endothelial cells are replaced by primary haemostasis with platelet plug, which then gets held together by fibrin.
Lots of endothelial cells die so there are lots of clots in the kidneys which consumes platelets. The deposited fibrin then slices RBCs up leading to MAHA.
There is also acute kidney injury
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Recognise the presenting symptoms of haemolytic uraemic syndrome
GI: severe abdominal colic, watery diarrhoea that becomes blood stained (due to the E Coli/shigella infection)
General: malaise, fatigue, nausea, fever <38 (in D+ form)
Renal: oliguria/anuria, haematuria
Recognise the signs of haemolytic uraemic syndrome on physical examination
General: Pallor (anaemia), slight jaundice (haemolysis), bruising (severe thrombocytopaenia), generalised oedema, HTN and retinopathy
GI: Abdo tenderness
Identify appropriate investigations for haemolytic uraemic syndrome and interpret the results
1st investigations:
FBC: anaemia, thrombocytopaenia
Peripheral blood smear:
To identify schichtocytes and to confirm the thrombocytopaenia
Renal function: Raised creatinine
Electrolytes: Abnormalities due to diarroeah or AKI. Include hyperkalaemia, hyponatraemia, acidosis etc.
PT, PTT: Both must be normal (if not, may suggest DIC)
Raised LDH from broken down RBCs
Low serum haptoglobin (it takes up haemolysed RBCs and then is removed by the liver/spleen)
Stool culture (SORBITOL-MACCONKEY AGAR) to detect shiga toxin producting E. Coli (needs to be done early in the course of diarrhoea though)
PCR to detect shiga toxin 1/2
Complement: abnormal levels of complement in familial and some cases of atypical HUS
The most common cardiac manifestation of SLE is
Pericarditis most common
Libman sacks endocarditis also common (this is also associated with antiphospholipid syndrome)
In antiphospholipid syndrome, who are arterial and venous thromboses more common in
What are the complications of each, generally and in APS
In APS there is a hypercoagulable state, causing thromboses in arteries and veins
Arterial thromboses more common in males.
Complications: heart attach, stroke, limb ischaemia
AND
(in APS) Libman Sacks endocarditis (vegetations (mixture of immune cells and blood clots) can affect the mitral valve)
Venous thrombosis more common in females. Typically present as DVT,
Complications: pulmonary embolism
Define vitamin B12
Which foods contain b12
Outline the normal absorption of b12
How much can the body store of b12
What is the job of b12
Reduced levels of vit b12 in the body
Present in egg, meat, milk but NOT in plants,
The protein containing the b12 is broken down using pepsin. It is then bound to IF (produced by gastric parietal cells). The b12-IF complex is recognised by the enterocytes lining the terminal ileum. Once absorbed, b12 is bound to transcobalamin
Body can store 4yrs of b12
Jobs:
- Allows conversion of dUMP to dTMP which is then converted into thymidine (essential for cell division)
- Also allows for conversion of homocysteine to methionine (too much homocysteine is harmful)
- Also helps to reduce methylmalonic acid
Explain the aetiology / risk factors of vitamin B12 deficiency
b12 deficiency results in reduced cell division and a build up of homocysteine and methylmalonic acid
BLOOD:
Macrocytes are produced which are destroyed in the spleen leading to anaemia, after which megaloblasts are released into the blood. Leads to macrocytic megaloblasic anaemia
Hypersegmented nuclei (>5 lobes)
Reduced production of megakaryocyte.
Can lead to pancytopenia (as can folate deficiency)
TONGUE:
Old epithelial cells aren’t replaced, reducing ability to heal when there is wear and tear of the tongue. This leads to inflammation= GLOSSITIS
ATHEROSCLEROSIS:
Homocysteine can bind to endothelial cells leading to proinflammatory cytokine release attracting immune cells. Narrowing of arteries and ischaemia. Homocysteine also increases increases platelet aggregation. So you are at increased risk of heart attack and stroke!
NEUROPATHY:
Methylmalonic acid can build up and accumulate in myelin sheaths, which causes it to degenerate. Can slow conduction in nerves and muscles. Subacute combined degeneration of the spinal cord
Reduced intake:
-(see above)
Reduced absorption:
-Crohn’s the enterocytes in terminal ileum might be damaged (so the b12 cannot bind to transcobalamin),
- Pernicious anaemia (IgA antibodies against IF OR the parietal cells),
- Gastric bypass (food passes through stomach quickly so IF can’t get to food to bind b12 fast enough) or gastric atrophy (reduced stomach acid production so not enough b12 is released)
- Diphyllobothrium latum (fish tapeworm) infestation/bacterial overgrowth
Risk factors:
Being long term vegan and not taking vit b12 supplements
What is subacute combined degeneration of spinal cord
Mix of UMN and LMN signs
UMN sign: symmetrical corticospinal tract loss, so causes UMN motor sign
LMN: Dorsal column loss causing LMN and sensory signs
Joint position and vibration affected first leading to ataxia followed by stiffness and weakness if untreated.
Classic triad: Extensor plantars (UMN), absent knee jerks (LMN) and absent ankle jerks (LMN)
Can present with falls at night time due to a combination of ataxia and reduced vision, which is also seen in b12 deficiency.
Pain and temperature may remain intact even in severe cases, as the spinothalamic tracts are preserved.
Recognise the presenting symptoms/signs of vitamin B12 deficiency
Anaemia:
-Pallor, SoB, easy fatigue
Soreness of tongue due to glossitis
Symptoms of IHD:
-chest pain, slurred speech, paralysis
Impaired neurological function:
-loss of memory function, reduced reflexes, psychosis
Identify appropriate investigations for vitamin B12 deficiency and interpret the results
Blood film (hypersegmented neutrophils, large RBCs)
MCV>100fL suggests macrocytosis
Bone marrow sample to look at megaloblastic changes in RBC precursors
Homocysteine and methylmalonic acid elevated
Look for anti-intrinsic factor antibodies for pernicious
Endoscopic or imaging if they could have crohn’s disease
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