Monday 20 September 2010

MRCP revision battle 16.1: Pagets disease of bone

In between catching up on seemingly endless loads of washing (do socks breed when left alone in a wash basket?) a few hours of MRCP revision has been done and 7 new battles have been written...

MRCP revision battle 16.1: Pagets disease of bone
MRCP revision battle 16.2: Pneumocystis carinii
MRCP revision battle 16.3: Myasthenia gravis
MRCP revision battle 16.4: Lambert-Eaton syndrome
MRCP revision battle 16.5: Hemiballismus
MRCP revision battle 16.6: Prolactin
MRCP revision battle 16.7: Erbs palsy

MRCP revision battle 16.1: Pagets disease of bone

Pagets disease of bone is accelerated, disorganised bone turnover due to increased number and activity of osteoclasts and osteoblasts.

It is rare in under 40s.

Predisposing factors include:
  • increasing age
  • northern latitude
  • family history
  • being male

Features of Pagets include:
  • bone pain
  • bowing of tibia
  • bossing of skull
  • secondary arthritis
  • deafness/other cranial nerve compression
  • high output heart failure
  • pathological fractures
  • bone sarcomas (occur in 1% over 10 yrs)

My way of remembering the features of pagets is this slightly random rhyming story:
"Bowing to the Boss, oh what a pain,
I'm deaf and arthritic and since the fracture I'm lame
my heart's now a failure, and oh what a shame
I've got bone sarcoma - thats the end of the game"

Bloods in Pagets show:
  • raised ALP
  • normal calcium (unless a long period of immobility)
  • normal phosphate

Treatment is alendronic acid

That wasn't too bad... onwards to battle 16.2...

MRCP revision battle 16.2: Pneumocystis carinii

Pneumocystis carinii, AKA pneumocystis jiroveci, is a unicellular eukaryote.

It can cause pneumonia in patients with HIV and accounts for 40% of all AIDS-defining illness.
If CD 4 count is less than 200 PCP prophylaxis (=co-trimexazole) should be started.

Features of PCP:
  •  dyspnoea
  • dry cough
  • fever
  • few chest signs on examination
  • desaturation on exercise

CXR typically shows mid-lower bilateral interstitial infiltrates, but it may look normal.

Sputum cultures are often negative so BAL may be needed.

Treatment is:
  • co-trimexazole
  • IV pentamidine if severe
  • steroids if hypoxia
    • use of steroids decreases respiratory failure by 50% and death by 1/3)

On to battle 3 of the day and a classic condition - myasthenia gravis.

MRCP revision battle 16.3: Myasthenia Gravis

Myasthenia gravis is an autoimmune condition in which muscles become easily tired and weak.  It affects 1 in 20 000.

90% of patients have autoantibodies to nicotinic acetylcholine receptors.
If these are negative consider looking for MUSK antibodies (= muscle specific kinase)

The key feature of MG is repetitive stimulation leading to decreased evoked response.

The order in which muscle groups are affected in MG is:
  • extraoccular (--> diplopia)
  • bulbar
  • face
  • neck
  • lumb
  • trunk

Reflexes are normal in MG.

Test of choice: tensilon test = edrophonium

Treatment of MG is:
  • cholinesterase inhibitors eg pyridostigmine
  • prednisolone if pyridostigmine unsuccessful (but be aware that paradoxically steroids can worsen MG)
  • plasmaphoresis/IV IG if respiratory muscle involvement.

If there is hyperplasia of thymus/thyroma, up to 60% of cases will remit after surgery.

Up to 10% of patients with MG will have hyperthyroidism.

Drugs which exacerbate MG include:
  • penicillamine
  • quinidine
  • beta blockers
  • lithium
  • phenytoin
  • gentamycin

Now on to the 'similar but different' Lambert-Eaton syndrome...

MRCP revision battle 16.4: Lambert Eaton Syndrome

Lambert-Eaton syndrome is a rare condition affecting voltage-gated calcium channels which results in:
  • muscular weakness that improves with activity
  • autonomic symptoms (dry mouth, constipation, impotence)
  • hyporeflexia

It is most commonly a paraneoplastic phenomenon, usually due to small cell lung cancer (very rarely due to breast or ovarian cancer).  It can also be autoimmune.

Treatment is 3,4 diaminopyridine.

Regular CXR should be performed as Lambert-Eaton may preceed the development of small cell lung cancer by up to 4 years.

Notice how although both MG and Lambert-Eaton are characterised by muscle weakness there are lots of differences - weakness gets worse on repetition in MG but better in LE, reflexes are normal in MG but reduced in LE and there may be autonomic symptoms in LE but not MG.  Also not involvement of occular muscles is far more common in MG.

Lets now diversify to something completely different - hemiballismus...

MRCP revision battle 16.5: Hemiballismus

Hemiballismus is large amplitude, flinging hemichorea.

Its cause is damage to the contralateral subthalamic nuclei.

The commonest cause is stroke.

  • hemiballismus generally resolves spontaneously in 4 to 8 weeks
  • haloperidol (a dopamine blocker) may be used
  • tetrabenazine (a VMAT inhibitor) may be used

Bilateral hemiballismus is rare and tends to be associated with HONK.

After that brief battle onwards to the meatier topic of prolactin

MRCP revision battle 16.6: Prolactin

Prolactin is a hormone released from the anterior pituitary.
It is under the negative control of dopamine (ie dopamine prevents its release)

Raised prolactin causes a drop in GnRH, LH, oestrogen and testosterone levels.

Symptoms/signs of raised prolactin include:
  • galactorrhoea
  • decreased libido
  • amenorrhoea
  • infertility

Note that gynaecomastia is NOT associated with raised prolactin.

Causes of a raised prolactin include:
  • physiological causes
    • pregnancy
    • breast feeding/nipple stimulation
    • stress
    • post-fit
    • exercise
  • drugs
    • phenothiazides
    • metoclopramide
    • methyl-dopa
    • haloperidol
    • oestrogens
  • metabolic causes
    • hypothyroidism
    • PCOS
    • acromegaly (1/3)
    • chronic renal failure
  • disease
    • prolactinoma
      • microprolactinoma (<10mm) release more prolactin than macroprolactinomas
    • compression of pituitary stalk removing dopamine control

Treatment is with bromocriptine.
It is best to give it in the evening as it causes postural hypotension

Very nearly there.  Last battle of the day will be Erbs palsy....

MRCP revision battle 16.7: Erbs palsy

Erbs palsy is the name given to a particular brachial plexus injury, generally caused by shoulder dystocia during birth.

Any nerve root of the brachial plexus may be affected but the most commonly affected roots are C5 and C6.

This results in loss of:
  • shoulder abduction
  • elbow flexion
  • suppination

The net outcome is that the arm hangs medially rotated with the forearm pronated = "waiters tip"

So thats all for today's battles - on to today's war to check recall of yesterday's battles!

MRCP questions: War 15

As with previous 'wars' after 'battles' these are just a few quick questions to see if your brain cells have retained the information provided in battles 15.1 to 15.8.

The answers are available here

Question 1:
List the 3 commonest sites of mets from renal cell carcinomas

Question 2:
What abnormalities on blood tests might you see with renal cell carcinoma?

Question 3:
What is Von Hippel Lindau disease?

Question 4:
A patient complains of severe right shoulder pain followed by weakness of the right arm.  There is no history of trauma.  What is the likely diagnosis?

Question 5:
A patient has abdo pain.  The busy nurse just leaves their urine sample in front of you.  Ten minutes later you notice it has turned deep red.  What condition does the patient have?

Question 6:
List 3 drugs that can precipitate acute porphyria

Question 7:
A medical student excitedly tells you the urine sample they've just taken glows pink under woods light.  What condition does the patient have?

Question 8:
Your newest patient has heart block, opthalmoplegia and pigmentary degeneration of the retina.  What test do you want to do to confirm your diagnosis?

Question 9:
List 7 symptoms associated with pellegra

Question 10:
Which drug is used to treat neuroleptic malignant syndrome?