Thursday 14 October 2010

MRCP revision battle 29.3: Hyperlipidaemia

This battle is quickly going to get complex and aims only to be an MRCP-focused overview rather than a comprehensive discussion.  It is divided into 5 stages:
  1. The basics
  2. Hypercholesterolaemia
  3. HDL - the good cholesterol
  4. Hypertriglyceridaemia
  5. Mixed



1. The Basics

Hyperlipidaemia = raised lipids.  Lipids come in 4 main 'flavours':

  1. chylomicrons = carry triglyceride
  2. LDL = mainly cholesterol (50%, 10% TG) = the 'bad' flavour
  3. HDL = mainly phospholipid = the 'good' flavour, carry cholesterol back to the liver
  4. VLDL = mainly triglyceride (60%, 20% cholesterol)

Signs:
  • corneal arcus = grey-white ring around cornea
  • xanthelasma = yellow collection of cholesterol under skin
  • xanthomata = 'lumps' of cholesterol
  • eruptive xanthomata = small yellow-orange papules that appear all over body
  • lipaemia retinalis = 'creamy' appearence of blood vessels on fundoscopy

So lets look first at cholesterol and hypercholesterolaemia.




2. Hypercholesterolamia

a. Familial
  • LDL receptor dysfunction
    • cholesterol 7.5-16
    • raised LDL
    • tendon xanthomata, corneal arcus and xanthelasma
    • heterozygous prevalance 1/500 --> MI in 40s
    • homozygous --> MI in 20s
  • Polygenic hypercholesterolaemia
    • cholesterol 6.5-9
    • raised LDL
    • xanthelasma and corneal arcus

 b. Acquired
  • nephrotic syndrome
  • renal transplant
  • cholestasis
  • hypothyroidism



3.  HDL

HDL is 'good' cholesterol

It is higher in:
  • thin people
  • exercise
  • oestrogens
  • alcohol
  • low triglycerides

It is lower in:
  • obesity
  • sedentary states
  • post-puberty males
  • smoking



4. Hypertriglyceridaemia

a. Familial
  • failure to metabolise chylomicrcons
  • features include:
    • eruptive xanthomata
    • lipaemia retinalis
    • retinal vein thrombosis
    • pancreatitis
    • hepatosplenomegaly

b. Secondary
  • diabetes
  • obestiy
  • alcohol
  • chronic renal failure
  • liver disease
  • drugs such as thiazides, beta blockers or oestrogens


5. Mixed hyperlipidaemia
  • Look for palar xanthomas and tuberous xanthomas


After that wordy and depressing battle, lets move on to treatment of hyperlipidaemia...