Friday 8 October 2010

MRCP revision battle 27.1: Heparin induced thrombocytopenia (HIT)

Today we have an epic set of battles with some real hard-hitters hidden amongst them, including sarcoidosis which is a differential for around 110% of MRCP questions (or at least thats what it feels like)   But if you get to the last battle you will be rewarded with lots of pictures (the joys of poikilocytosis) and then a link to look at some interesting non-medical pictures...

So the carrot is dangled, and here are the sticks:

MRCP revision battle 27.1: Heparin induced thrombocytopenia (HIT)
MRCP revision battle 27.2: Sarcoidosis
MRCP revision battle 27.3: Lofgren's syndrome
MRCP revision battle 27.4: Pancreatitis
MRCP revision battle 27.5: Visual field defects
MRCP revision battle 27.6: Paroxysmal nocturnal haemoglobinuria
MRCP revision battle 27.7: Poikilocytosis

MRCP revision battle 27.1: Heparin induced thrombocytopenia (HIT)

Heparin induced thrombocytopenia is one of those fabulous conditions whose name explains it all: low platelets, caused by heparin.  It is often abbreviated to HIT, which confused me greatly when I first had a patient affected by it and my consultant declared "ah, he's got HIT" which made me wonder who he was suspecting of abuse on the ward...

Technically there are 2 types of HIT:
  • Type 1 - occurs in first 2 days, is non-immune and the platelet count spontaneously recovers 
  • Type 2 - occurs 4 to 10 days after starting heparin, is immune-mediated and potentially life-threatening.

However, when HIT is mentioned, people generally mean type 2.

HIT is caused by antibodies against the heparin-platelet factor 4 complex.  These antibodies can be found in 90% of patients with HIT... but may also be present in unaffected patients taking heparin.

Ironically, although HIT is characterised by low platelets it is an incredibly pro-thrombotic condition.  As a result patients are likely to get PEs/DVTs and warfarin must absolutely not be started (since warfarin is initially prothrombotic too).  As you can see HIT causes something of a management problem - thrombosis due to the treatment you would give for thrombosis...

Management of HIT will involve specialist haematological input but in terms of MRCP question answers think:
  • stop heparin
  • stop/reverse warfarin
  • give lepirudin (=highly specific direct inhibitor of thrombin)

Note that HIT is more likely with unfractionated than LMW heparin.

Onwards to sarcoidosis...

MRCP revision battle 27.2: Sarcoidosis

Sarcoidosis is a multi-system granulomatous disorder of unknown cause.

It is asymptomatic in up to 40% of cases, being discovered incidentally on a routine CXR.

Features of sarcoidosis may be divided into pulmonary and non-pulmonary:

Pulmonary features of sarcoidosis:
  • dry cough
  • progressive dyspnoea
  • chest pain

Non-pulmonary features of sarcoidosis include:
  • lymphadenopathy (commonest in non-whites)
  • erythema nodosum (commonest in white females)
  • polyarthralgia
  • hepatomegaly
  • splenomegaly (around 25%)
  • anterior uveitis (around 25%)
  • glaucoma
  • Bells palsy
  • lupus pernio
  • hypercalcaemia
  • renal stones
  • pituitary dysfunction
  • cardiomyopathy...

90% of patients with sarcoid will have an abnormal CXR.
Staging of CXR in sarcoid is:
  • 0 = clear CXR
  • 1 = bilateral hilar lymphadenopathy
  • 2 = bilateral hilar lymphadenopathy plus pulmonary infiltration
  • 3 = pulmonary infiltration only
  • 4 = fibrosis, honeycombing, pleural involvement

  • raised ESR
  • lymphopenia
  • raised LFTs
  • raised serum ACE
  • raised calcium (5%)
  • tuberculin skin test is positive in around a third

  • BHL alone doesn't need treatment
  • acute sarcoidosis : NSAIDs and bed rest
  • prednisolone ( 40mg OD for 4-6 weeks then reducing dose over one year) is indicated if:
    • parachymal lung disease
    • uveitis
    • hypercalcaemia
    • neurological/cardiac involvement

Lets move on to briefly consider lofgrens syndrome...

MRCP revision battle 27.3: Lofgren's syndrome

Lofgrens syndrome is a subtype of sarcoidosis, characterised by:
  • erythema nodosum
  • bilateral hilar lymphadenopathy
  • fever
  • athralgia

It affects females more than males (85:15)

It carries a good prognosis - unlike sarcoidosis is unlikely to become chronic and most cases resolve in 6 months to 2 years.

On to something which often doesn't have a good prognosis... pancreatitis...

MRCP revision battle 27.4: Pancreatitis

Acute pancreatitis tends to present as epigastric/central abdominal pain radiating to the back with vomiting.  The pain may be improved by sitting forward.

Signs may be few; periumbilical discoloration (Cullen's sign) or flank discoloration (Grey Turner's sign) are rare.

Causes of pancreatitis can be remembered by I GET SMASHED:
  • idiopathic
  • gallstones
  • ethanol
  • trauma
  • steroids
  • mump
  • autoimmune
  • scorpion venom
  • hyperlipidaemia, hypercalcaemia, hypothermia
  • ERCP
  • drugs (steroids, ocreotide, sulphonamides, tetracyclines, azathioprine, sodium valproate)

  • bloods including amylase 
    • note amylase normalises in 24-48hrs; serum lipase is more sensitive and specific
  • AXR: ?sentinel loop ?loss of psoas shadow
  • CT abdo is the investigation of choice
  • score using the Modified Glasgow criteria.

Modified Glasgow criteria (helpfully spells out 'pancreas'):
  • Pa O2 <8
  • Age >55
  • Neurophils: WCC >15
  • Calcium: <2
  • Renal function: urea >16
  • enzymes: LDH >600; AST >200
  • Albumin: <32
  • Sugars: glucose >10
3 or more suggests severe pancreatitis.

Management of acute pancreatitis is:
  • lots of IV fluid, catheter for fluid balance
  • analgesia
  • close observation
  • treat cause

Complications of pancreatitis include:
  • early
    • sepsis
    • shock
    • ARDS
    • renal failure
    • DIC
    • hypocalcaemia
    • hyperglycaemia - 5% need insulin
  • late
    • necrosis and pseudocyst (=fluid in lesser sac)
    • abscess
    • fistulae
    • chronic pancreatitis

Now for something completely different, visual field defects...

MRCP revision battle 27.5: Visual field defects

Visual fields pop up frequently in MRCP questions so it pays to learn this well!

The basic anatomy is illustrated below:

Armed this this anatomy lets look at the various patterns of field defect...

1: Bitemporal hemianopia
  • caused by compression of the optic chiasm
  • upper affected more than lower = due to pituitary tumour
  • lower affected more than upper = due to craniopharyngioma
  • I personally remember this as UP  London City

2: Homonymous quadrantanopia

  • superior homonymous quadrantanopia is a lesion in the temporal lobe
  • inferior homonymous quadrantanopia is a lesion in the parietal lobe
  • this can be remembered by thinking PITS - parietal inferior temporal superior
  • if the defect is incongruous it is in the optic tract
  • if the defect is congruous it is in the optic radiation/cortex

3: Homonymous hemianopia
  • injury to the brain (eg bleed, tumour) on the opposite side to the field defect

4: Central scotoma

  • usually caused by optic neuritis

5: Binasal hemianopia
  • rare
  • ?calcification of carotids

Note that the fovea is supplied by both the PCA and MCA so may be spared in a PCA CVA.

In the calcarine sulcus peripheral regions are processed anteriorly while central regions are processed posteriorly.

Finally remember cortical blindness:
  • caused by bilateral occipital infarcts
  • pupillary responses are preserved
  • possibly small macular sparing
  • patient may deny they have vision loss (=Anton's syndrome)

Wow, that was lots for one battle... lets move on to some urine for light relief...

MRCP revision battle 27.6: Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria is a condition in which blood cells are sensitive to complement-mediated lysis due to an inherited lack of surface glucosylphosphatidylinositol (GPI)

Features of paroxysmal nocturnal haemoglobinuria include:
  • cola coloured/red urine in morning due to increase in RBC lysis overnight
  • intravascular haemolysis
  • pancytopenia
  • thrombosis

Diagnosis is by urinary haemosiderin or + Ham's test (rarely done now)

Treatment is anticoagulation, transfusions when needed and possibly the smart new monoclonal antibody called eculizimab.

Now on to the last battle and some pretty pictures...

MRCP revision battle 27.7: Poikilocytosis

Poikilocytosis = abnormality of red blood cell shape.

Here's a quick crash course of the various shapes and their causes.  Blood slides are all from wiki commons.

1. Teardrop cells - myelofibrosis

2. Helmet cells - microangiopathic haemolytic anaemias

click here to link to an image covered by copyright

3. Elliptocytes = Pencil cells - seen in hereditary elliptocytosis and iron deficiency

4. Sickle cells - seen in sickle cell disease

5. Spherocytes - seen in any haemolysis and in hereditary spherocytosis

6. Target cells - seen in liver disease, post splenectomy, iron deficieny, thalassaemia, haemoglobinopathies

click here to link to an image covered by copyright

7. Acanthocyte/burr cell - acanthocytes are seen in liver disease.  Burr cells (=slightly less spikey than acanthocytes) appear in uraemia.

8. Schistocyte  = shredded red blood cells, seen in DIC, mechanical heart valves, microangiopathic diseases, haemolytic anaemias

Thats all the battles for today; as promised at the beginning  click here if you want to see some interesting pictures of what your workplace might look like if abandoned for a few years...