Haem Flashcards
LO1: Basics of purine metabolism
Purines are broken down to form hypo-xanthine and sequentially oxidised by xanthine oxidase to form urate.
Clinical features of acute gout
- Rapid build up of paint
- “Exquisite pain”
- Affected joint red, hot, swollen
- Most common joint = 1st MTP joint of the big toe
- Management = Reduce inflammation (vs managing hyperuricaemia more for chronic gout) - impt differentiator
Gout aetiology + epidemiology
- Crystal arthropathy - monosodium urate crystals
- Needle shaped crystals - sets off intensive inflammatory reactions
- Epidemiology
- Males 3% (post puberty except Lesch Nyhan)
- Females 0.5% (more common post menopause)
Why do humans have issues with urate
In other animals, urate is then broken down to form allantoin by urease.
Allantoin is highly water soluble and freely excreted in the urine.
we do not have functional urease (while we do have the rudimentary gene)
- Urate is relatively insoluble
- Urate circulates in the bloodstream at concentrations just below it max solubility, meaning that it is constantly on the brink of precipitating out to form urate crystals.
Plasma concentrations of monosodium urate
- Men: 0.12-0.42 mmol/l
- Women: 0.12-0.36 mmol/l (one reason why women get less gout than men)
- Solubility at 37oC = 0.40mmol/l
- Solubility drops at cooler temperature and lower pH (more acidic)
3 Key Principles of purine metabolism
- You can make purines by 2 ways: de novo synthesis (green box) or salvage mechanism aka recycling (blue box)
* De novo = difficult, inefficient, highly metabolically expensive, body only uses this if there is extremely high requirements of purines e.g. bone marrow due to high cellular division whereby salvage alone is insufficient
* Salvage = highly energy efficient, body predominantly uses this pathway - Rate limiting step in de novo purine synthesis is catalysed by enzyme PAT (PPRP Amido Transferase)
*
* PAT under feedback inhibition by outputs GMP and AMP (the left and right dotted arrows)
* PAT is also under feed forward effect whereby activity is stimulated by higher levels of PPRP (substrate)
* Break and accelerator example - HPRT/HGPRT = hypoxanthine-guanine phosphoribosyltransferase is the main enzyme that recycles partially catabolised purine and bring them back up the metabolic pathway (salvage pathway)
* Absolute deficient = Lesh Nyhan
* No HGPRT = no recycling of purines to GMP or IMP
* Lack of GMP/IMP = reduced negative inhibition of PAT
* De novo synthesis pathway goes into overdrive, excessive purine synthesis
* The massive loads of purines has no where else to go (because there is not corresponding need) and is broken down the purine pathway (IMP → Inosine → hypoxanthine → Xanthine → Urate)
* Additionally, lack of guanine recycling causes accumulation of PPRP (forward accelerator)
Two types of gout
- Acute - Podagra (pod/foot aggravation)
- Chronic - Tophaceous (not acute pain but chronic deposition of urate crystals in soft tissue, tophi in earlobes and adjacent to joints- chalky, cottage cheese)
Treatment acute gout (reduce inflammation)
- NSAIDS (1st line)
- Colchicine (2nd line, inhibit polymerisation of tubulin which in contact of gout 1. reduce cell turnover and 2. reduce motility of neutrophils to prevent neutrophils from participating in inflammation)
- Glucocorticoids
- DO NOT ATTEMPT TO MODIFY PLASMA URATE CONCENTRATION (reducing can paradoxically increase urate crystal formation)
Treatment chronic gout or interval non-acute attacks (managing hyperuricaemia)
- Drink plenty water
- Reverse factors putting up urate (diuretics especially thiazide diuretics)
- Reduce synthesis with allopurinol (inhibit xanthine oxidase)
- Increase renal excretion with probenecid (uricosuric)
Allopurinol cannot be given with ____ + why
- Do not give together with AZATHIOPRINE - steroid sparing agent, used to gently suppress bone marrow to act as immune suppressor, prodrug for 6-mercaptourine → thioinosinate which interfere with purine metabolism
- If given with allopurinol which is inhibitor of xanthine oxidase and given azathioprine (which makes purine and adds to purine pathway), you amplify the effects of azathioprine to toxic levels = shut down bone marrow and result in pancytopenia (cardinal medical sin - also do not give trimethoprim with methotrexate)
Diagnosis of gout (3)
- Tap effusion
- View under polarised light
- Use red filter
Study birefringence
- birefringence = property of the crystal to rotate the axis of the polarised light
- Urate crystals = negatively birefringence (urate crystal = needle light = negative)
- Negative means it rotates 90 degrees to the filter (blue needle)
- Pyrophosphate (psuedogout) is blue in the axis of the red compensator (py = positive)
Psuedogout
(the only other crystal arthropathy)
- Occurs in patients with osteoarthritis
- Pyrophosphate crystals
- Self-limiting 1-3 weeks
- Affects different joints (osteo joints)
- Positively birefringence, blue in line with axis of red compensator
Diagnostic requirement for coeliac disease
endomysial antibodies and tissue transglutaminase antibodies
Duodenal biopsy of pt with coeliac disease will show
On gluten rich diet showing villous atrophy
Off gluten showing normal villi
MALToma associated with Coeliac found in the _______ and is B/T lymphocyte origin
MALToma associated with Coeliac found in the duodenal and is of T lymphocyte origin (Enteropathy Associated T-cell lymphoma)
Treatment for essential thrombocytopenai
Treatment
- Aspirin - prevent thrombosis
- Anagrelide - inhibition of platelet function (SE palpitations and flushing)
- Hydroxycarbamide - antimetabolite, suppress other cells, mildly leukaemogenic
What should you think of when you see leuco-erythroblastic blood film?
Bone marrow
Means there is infiltration
What causes leuco-erythroblasti blood film?
- Root issue: bone marrow infiltration by
- Cancer
- Haemopoietic: leukaemia/lymphoma/myeloma
- Non-Haemopoieotic: breat/bronchus/prostate
- Severe infection
- Military TB
- Severe fungal infection
- Myelofibrosis
- Masive splenomegaly
- Dry tap on BM aspirate
- Cancer
Morphological features of leuco-erythroblastic blood film
- Teardrop RBC
- Nucleated RBC
- Immature myeloid cells
Fe deficiency is always due to ____ unless proven otherwise
OCCULT BLOOD LOSS
from GI cancers or urinary tract cancers
Common distinguishing features of haemolysis of RBC
- Anaemia (though may be compensated)
- Reticulocytosis
- Raised bilirubin (unconjugated)
- Raised LDH (intracellular enzyme released into plasma when RBC lyse)
- Reduced haptoglobin (because haptoglobin binds to free haemoglobin in the blood released from lysed cell)
Causes of inherited haemolytic anaemia
Think of the structure of RBC
Membrane:
- hereditary spherocytsis
- hereditary elliptocytosis
Enzyme:
- G6PD def
- pyruvate kinase def
- Pyrimidine-5’-nucleotidase def
Hb:
- Thalassaemia (number)
- Sickle cell disease (functional)
- unstable Hb variant
Features that suggest this haemolytic anaemia is inherited
Are the common lab features of all Haemolytic anaemia present?
Ethnic background (why are these anaemias so common worldwide?)
Is there a family history/lifelong history with first presentations in childhood/recurrent episodes?
Pigment gallstones?
What is one test to distinguish between immune and non-immune causes of haemolytic anaemia
Direct Antiglobulin (DAT or Coombs test)
Autoimmune and non-immune causes of acquired haemolytic anaemia
Auto-immune causes of acquired haemolytic anaemia
- Spherocytes, DAT+ve
- Cancer of immune system: lymphoma
- Disease of immune system: SLE
- Infection affecting the immune system: EBV, HIV
Non-immune causes of acquired haemolytic anaemia
- Infection (malaria)
- MAHA
- Red cell fragments
- Low platelets
- Bleeding/DIC
- Underlying adenocarcinoma
Haemolytic aneamis associated with systemic disorders
Associated systemic disorder
Cancer of immune system: lymphoma
Disease of the immune system: SLE
Infection (disturbing the immune system)
Explain how adenocarcinomas or DIC causes acquired, non-immune haemolytic anaemia
- Consume platelets (in DIC)
- Coagulation activation (cancer)
- Formation of fibrin strands - cheese strings
- Red cells pushed through this mesh at high pressure due to BP
- SHEEEEEAAAARRRR - red cell fragmentation (microangopathy)
- Haemolysis
List the primary and secondary causes of TRUE polycythaemia
primary (low EPO)
* Polycythaemia vera - clonal proliferation of red cells from acquired mutations in JAK2
Secondary (high EPO)
- Appropriate causes - high altitude, hypoxia, cyanotic heart disease, high affinity haemoglobin
- Inappropriate - liver cancer, renal disease (EPO tumours), lung cancer
Female aged 39 treated breast cancer 4 years previously
- recent onset jaundice and hepatomegaly
- GP bloods
- Hb 87g/l
- Reticulocyte 15x10^9/L (20-92)
- Bilirubin 50 micromol/l conjugated
DAT negative
Blood film
- leuco-erythroblastic anaemia
- leuco-erythroblastic anaemia think bone marrow
Infiltrates from cancer or infections
In this lady probably her breast cancer mets to liver and bone marrow
Investigation of raised white cell from a blood test
What do you want to do/investigate?
Ask for blood film - are the cells mature or immature? And there features
What lineage - specific e.g. granulocytes or all (granulocytes + lymphocytes)
How high?
Causes of neutrophilia
- infection (reactive)
- cancer (myeloproliferative disorders, leukaemia disorder)
- tissue inflammation (e.g. pancreatitis, colitis)
- underlying neoplasia
- corticosteroids
What infections classically do not produce neutrophilia
brucella, typhoid, many viral infections.
What features of the neutrophil on the blood film and pt would suggest this is a reactive neutrophilia?
Presence bands, toxic granulation (vacuoles), and clinical signs of infection/inflammation (pyrexia, abscess, raised X? protein
What features on a blood film suggest malignant increase in WBC?
Neutrophilia, basophilia plus immature cells myelocytes, and splenomegaly. Suggest a myeloproliferative (CML)
Neutropenia plus Myeloblasts (AML)