MRCP revision battle 35.1: Graves' disease

Today is going to be a bit of a thyroid binge with a little gap to end on...


MRCP revision battle 35.1: Graves' disease
MRCP revision battle 35.2: Subacute (de Quervain's) thyroiditis
MRCP revision battle 35.3: Hashimoto's thyroiditis
MRCP revision battle 35.4: Drugs causing hypothyoidism
MRCP revision battle 35.5: Thyroid storm
MRCP revision battle 35.6: Anion gap




MRCP revision battle 35.1: Graves' disease


Graves' disease is an autoimmune condition which causes hyperthyroidism.  Autoantibodies against the thyroid gland are present.  This may be antithyroid peroxidase antibodies or antithyroglobulin antibodies (neither are specific as they may also found in Hashimotos)  or TSH receptor antibody (specific)


Features of Graves' disease include:

• eye disease (see revision battle 29.2 to recap which features are Graves' disease specific)
• pretibial myxoedema - only found in Graves
• thyroid acropachy = clubbing, painful toe and finger swelling - also only in Graves
• diffuse thyroid enlargement

Associated with Graves' disease include:

• diabetes 
• vitiligo
• Addisons

Treatment options for Graves are:

1. titrate antithyroid drugs
• start at 40mg carbimazole
• continue for 12-18 months
• less side effects
2. block and replace
• start at 40mg carbimazole, levothyroxine once euthyroid
• treat for 6 to 9 months
• more side effects
3. radioiodine

on to battle 35.2...

MRCP revision battle 35.2: Subacute (de Quervain's) thyroiditis

Subacute (de Quervain's) thyroiditis is the label given to a viral infection which causes a painful goitre and potentially transient hyper or hypo thyroidism.


In addition to a painful goitre the patient may have a fever and dysphagia.


Classically it occurs following a upper respiratory tract infection but it may occur after any viral illness (mumps, adenovirus) and also post-partum.


Histology would show multi-nucleated giant cells.
Radioiodine uptake is typically less than 1% at 24 hrs.


Treatment is with NSAIDs.  It resolves spontaneously.


Onwards to Hashimotos...

MRCP revision battle 35.3: Hashimoto's thyroiditis

Hashimoto's thyroiditis is an autoimmune condition causing hypothyroidism.


It is associated with high titres of antithyroid peroxidase antibodies or antithyroglobulin antibodies (neither are specific as they may also found in Graves' disease)


Patients with Hashimotos have a goitre due to lymphocytic and plasma cell infiltration.  The gotire is firm and non-tender.


Clinically patients' with Hashimotos may be hypothyroid, euthyroid or occasionally initially even hyperthyroid!



So lets move away from this autoimmune cause of hypothyroidism to look at drugs causing hypothyroidism...

MRCP revision battle 35.4: Drugs causing hypothyoidism

Drugs which can cause hypothyroidism include:

• lithium
• interferon
• amiodarone
• phenytoin
• aspirin
• oestrogens
• furosemide

 On  to the final bit of thyroid for the day: thyroid storm

MRCP revision battle 35.5: Thyroid storm

Thyroid storms may be precipitated by:

• recent thyroid surgery
• radioiodine
• infection
• MI
• trauma

Iatrogenic thyroxine excess doesn't usually cause a storm.


Features of a thyroid storm include:

• fever >38.5C
• tachycardia
• confusion
• nausea and vomiting
• hypertension
• heart failure

Treatment:

• treat precipitating event
• propranolol
• antithyroid drugs eg propylthiouracil or carbimazole
• dexamethasone/hydrocortisone - blocks T4 to T3 
• Lugol's solution
• ?digoxin to slow heart.

Thats the end of the thyroid binge - now to 'mind the gap..'

MRCP revision battle 35.6: Anion gap

If you have a patient with metabolic acidosis you need to calculate their anion gap.  This is very simple to do, so long as you can remember the following formula (which unfortunately I never can):

Anion gap = (Na + K) - (Cl + HCO3)

A 'normal' anion gap is 10 to 18mmol/l (which can be recalled as roughly the ages you attend secondary school for)


Causes of a raised anion gap may be recalled as LUKES:

• lactic acid (shock, infection, hypoxia)
• urate (renal failure)
• ketones (diabetes, alcohol)
• ethylene glycol/methanol
• salicylate

A more comprehensive list can be recalled by 'cute dimples' = cyanide, urate, toulene, ethylene glycol, diabetic ketoacidosis, isoniazid, methanol, propylene glycol, lactic acid, salicylates




Causes of a metabolic acidosis with a normal anion gap can be recalled as FUSEDCARS:

• fistula (pancreatic)
• uretogastric conduits
• saline administration
• endocrine (hyperparathyroidism)
• diarrhoea
• carbonic anhydrase inhibitors (acetazolamide)
• ammonium chloride
• renal tubular acidosis
• spironolactone

Hopefully thats demystified the anion gap for you.