BOF: 2.70
A 53-year-old female who was on amiodarone presents with weight loss
despite a good appetite, heat intolerance, tremors and excessive sweating.
On examination she has exophthalmos and a palpable goitre. Pulse rate
was 120 beats per minute regular and she had a fine tremor of her hands
Thyroid function tests showed the following values: thyroid stimulating
hormone (TSH), < 0.03 mIU/L (normal, 0.5-5.0 mIU/L); thyroxine (T4),
15.3 µg/dL (normal, 4.0-10.5 µg/dL); triiodothyronine (T3), 256
ng/dL (normal, 80-200 ng/dL); free thyroxine index (FT4I), 19.4
(normal, 4.7-10.0). She was positive for thyroid peroxidase (“microsomal”) antibodies, and
thyroid stimulating immunoglobulin.
In this patient the most
suitable initial treatment would be a combination of:
a) Steroids and azathioprine
b) Carbimazole and radioactive
iodine
c) Potassium perchlorate and
carbimazole
d) Carbimazole and surgery
e) Steroids and carbimazole
Answer: c)
The clinic features suggest
the patient has thyrotoxicosis. Amiodarone may induce thyrotoxicosis.
There are
two types of amiodarone-induced thyrotoxicosis:
Type I
caused by excess iodine in amiodarone (usually occurs where there is latent
disease in the thyroid; Graves’ disease or nodular goiter)
Type 11
which is a thyroiditis induced by amiodarone (normal thyroid)
Treatment of the two types is
different
Treatment of amiodarone-induced thyrotoxicosis
Type 1
Thionamide (methimazole,
carbimazole, propylthiouracil)
Potassium perchlorate
Type 2
Prednisolone
Hence it is important to
differentiate the two types before commencing treatment. This can be
difficult.
The following table will help:
|
|
Type I |
Type II |
|
Goitre |
Present |
Absent |
|
Thyroid antibodies (microsomal, thyroglobulin, anti
receptor |
Present |
Absent |
|
Interleukin levels |
Normal |
Raised |
|
Colure flow Doppler sonography |
Increased flow |
Decreased flow |
In this patient the features of goitre, exophthalmos suggest she
has pre-existing thyroid disease and hence would favour type I amiodarone
induced thyrotoxicosis.
The presence of thyroid antibodies lends further weight to this
diagnosis.
