Aetiology and diagnosis
- Affects 2% women and 0.2% of men
- The commonest causes are
- Graves disease
- Toxic nodular goitre
- Toxic solitary nodule
- Thyroiditis
- Serum free T4 is normally increased
- Serum total T4 can be variable due to changes in serum levels of thyroid binding globulin
- Occasionally free T3 is increased in T3-toxicosis
- Diagnosis of thyrotoxicosis can be confirmed by the measurement of TSH level
- A normal TSH excludes the diagnosis (except in rare case of TSH secreting pituitary tumours)
Clinical features of thyrotoxicosis
- Palpitation, tachycardia, cardiac arrhythmias, cardiac failure
- Sweating, tremor
- Hyperkinetic movements
- Nervousness
- Myopathy
- Tiredness and lethargy
- Weight loss
- Heat intolerance
- Diarrhoea and vomiting
- Irritability
- Emotional disturbance
- Behavioural abnormalities
- Ophthalmic signs
- Irregular menstruation and amenorrhoea
- Pretibial myxoedema
- Thyroid acropachy
- Vitiligo
- Alopecia
Pretibial myxoedema
- Occurs in 1-2% patients with Graves' disease
- Painless thickening of the skin in nodules or plaques
- Usually occurs on shins or dorsum of foot
- Strongly associated with ophthalmopathy
Thyroid acropachy
- Occurs in less than 1% patients with thyrotoxicosis
- Closely resembles finger clubbing
- Almost all patients also have ophthalmopathy or pretibial myxoedema
Graves' disease
- Usually occurs in women between 20 and 40 years
- Immunological disorder due to release production of thyroid stimulating IgG antibodies
- Bind to TSH receptor stimulating thyroid hormone production
- Produces a diffuse goitre
- Clinically patients have features of thyrotoxicosis often with eye signs:
- Exophthalmos and proptosis - usually bilateral
- Diplopia due to weakness of external ocular muscles
- Chemosis and corneal ulceration
Treatment of thyrotoxicosis
- Rapid symptomatic relief can be achieved with beta-blockers
Thyroid function can be reduced by
- Anti-thyroid drugs
- Radioactive iodine
- Surgery
Anti-thyroid drugs
- Inhibit synthesis of thyroxine by reducing incorporation of iodine into tyrosine residues
- Most commonly used drugs are carbimazole and propylthiouracil
- Used short-term (3-4 months) prior to definitive treatment (radioiodine or surgery)
- Used long-term (12-24 months) induce remission in Grave's disease
- 40% of patients with Grave's disease respond to carbimazole
- Side effects of carbimazole include agranulocytosis, aplastic anaemia, hepatitis
- Patients need to be warned to seek medical attention if they develop sore throat etc.
- Advantage - no surgery or the use of radioactive materials
- Disadvantages
- Treatment is prolonged
- Failure rate after 2 years treatment is approximately 50%
- Impossible to predict which patients will remain in remission
- Some goiters enlarge during treatment
Radioactive iodine
- 131I is commonest isotope used
- 400 MBq renders 50% patients hypothyroid but about 20% remain hyperthyroid
- Contraindicated in children, pregnancy and breast feeding
- Pregnancy should be avoided for 4 months after treatment
- Advantage - no surgery or prolonged drug therapy
- Disadvantages
- Isotope facilities must be available
- 80% hypothyroid at 10 years
- Indefinite follow up required
Surgery
- Indications for surgery in Grave's disease are:
- Relapse after adequate course of anti-thyroid drugs
- Large goitre
- High T4 levels at diagnosis (>75 pmol/l)
- Subtotal thyroidectomy is treatment of choice.
- Preserves about 4g (10%) of thyroid tissue
- Patients must be euthyroid prior to operation
- Advantages - goitre is removed and cure rate is high
- Disadvantages
- 5% develop recurrent thyrotoxicosis
- 20% develop postoperative hypothyroidism
- 0.5% develop parathyroid insufficiency
Picture provided by Zhao jun, Second Hospital of Xijan, Jiaotong University, China
Thyroid storm
- Uncommon life-threatening exacerbation of thyrotoxicosis
- Has a mortality of 50%
Precipitating factors
- Thyroid surgery
- Radioiodine
- Withdrawal of antithyroid drugs
- Iodinated contrast agents
- Acute illness (e.g. stoke, infection, trauma)
Clinical features
- Severe thyrotoxicosis
- Fever
- Delirium
- Seizure or coma
- Jaundice
Treatment
- Propylthiouracil 600mg loading dose
- Lugol's iodine at least one hour later
- Beta-blocker
- Supportive measures
- Treatment of precipitating cause
Bibliography
Franklyn J A. The management of hyperthyroidism. N Eng J Med 1994; 330: 1731-1738.
Sheldon J, Reid D J. Thyrotoxicosis: changing trends in treatment. Ann R Coll Surg
Eng 1986; 68: 283-285.
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