Haematology in MRCP(2)-Sickle Cell Disease

Haematology in MRCP(2)-Sickle Cell Disease

Sickle Cell Disease
Sickle cell disease is an inherited blood disorder that affects red blood cells. It is a type of hereditary haemoglobin disorder where valine has been substituted for glutamic acid at position 6 of haem beta chain, caused by a point mutation. You must remember that Sickle Cell Disease (SCD) is inherited in a Mendelian recessive manner. Therefore patients with two Sickle genes (SS) or carry one S gene but with concomitant Beta Thalassemia ( SB) are affected.

This disease is common in peoples of Equatorial African ancestry.

Clinical Presentations

Remember that all clinical features are due to two main features of the disease- haemolysis and vaso-occlusive crisis. You must understand that HbS is insoluble in the dexoygenised form and they have a shorter life span due to increased fragility, therefore causing chronic haemolysis ( similar to Thalassemia). The red blood cells with HbS also tend to aggregrate and cause thrombosis, this will leads to tissue infarction. Remember that the vaso-occlusive crisis tends to be precipitated by HADI ( hypoxia, acidosis,dehydration and infection)

Clinical features due to haemolysis

Anemia
Gallstone
Bone marrow enlargement
( these features also occur in Thalassemia patients)

Clinical fatures due to vaso-occlusive crisis

Bone pain- may cause vascular necrosis

Humerol head avscular necrosis

Leg ulcers
Genito-urinary- priapism
Cerebral-stroke
Spleen- initially may cause splenomegaly due to extra medullary haemopoiesis ( due to anemia) but later splenic infarct and hyposplenism. Patients tend to have capsulated bacteria infection and Salmonella osteomyelitis.
Chest-acute chest pain
( remember that these are all due to thrombotic events)

Physical Signs
Patients tend to be pale with jaundice. Hepatomegaly may be present. Look for chronic leg ulcers.

Investigations

Full blood count- low Hb with features suggesting haemolysis such as increased reticulocyte counts
LFT- increased bilirubin and AST
Peripheral blood film- sickled cells
Haemoglobin electrophoresis- to determine variant haemoglobin
X-ray- to look for vascular necrosis if patients present with joint pain.

Management

During sickle crisis ( oxygen, analgesia, rehydration)
Long term management
- prophylactic penicillin for prevention of penumococcal infection,
- management of anemia, however be careful about secondary iron overload due to multiple transfusions
- folate supplements

Tips for MRCP

1) Always suspect Sickle Cell Disease if a patient has anemia and chronic leg ulcers.

Haematology in MRCP-Polycythaemia

Haematology in MRCP(1)- Polycythaemia

I am going to talk about a few important topics that are frequently asked in haematology, MRCP. The first topic that I want to talk about is polycythaemia.

Polycythaemia or erythrocytosis is defined as an increased concentration of red cells, usually with a corresponding increase in hemoglobin level.

I find the following classification of polycythaemia useful and easy to remember.


There are two main types of polycythaemia- Relative polycythamia ( pseudopolycythaemia) or absolute polycythaemia ( true polycythaemia).

Relative polycythaemia means that the absolute red cell counts are normal but due to haemoconcentration because of decreased plasma volume, patient’s haemoglobin is raised. This can be due to any kind of dehydration, however, there is a popular condition often asked in MRCP, it is an obscure condition of unknown origin known as Gaisbock’s syndrome (stress polycythaemia). It is a kind of relative polycythaemia.

For true polycythaemia, the absolute red cell counts are raised and it can be subdivided into either primary ( without obvious reason) or secondary ( with an underlying reason). For primary cause, the most important disease you must learn is polycythaemia rubra vera which I will cover in my future post. For secondary polycythaemia, the haemoglobin can be raised appropriately ( due to increase physiological need) or inappropriately.

There are three common tumours that cause secondary polycythaemia- namely renal cell carcinoma, hepatoma and hemangioblastoma ( very popular question in MRCP!). As for the examples of appropriate secondary polycythaemia, the causes are easy to remember because patients with all these conditions are hypoxia chronically, therefore they need an increase haemoglobin level to survive!