Case Discussion - Thyroid Gland

Q. What is your diagnosis ?
A1. Toxic diffuse goitre (1ry toxic goitre)
A2. Toxic nodular goitre (2ry toxic goitre)
Q. Why this is a goitre ?
A. Because there is a swelling in the lower part of
the front of the neck which is the anatomical site
of the thyroid gland, having the shape of the
thyroid gland (butterfly) and this swelling moves
up and down with deglutition.
Q. Why it is toxic ?
A. Because the patient has manifestations of
thyrotoxicosis in the form of:
• From history : Palpitation, nervousness,
irritability, intolerance to hot weather,
increased appetite associated with loss of
weight ,
• From general examination : Tachycardia,
arrhythmia, tremors, eye signs of
thyrotoxicosis
• From local examination : Dilated veins,
expansile pulsations, warmth, palpable thrill,
audible bruit..
Q. What are the eye signs of thyrotoxicosis ?
A.
1. Infrequent blinking (staring look)
2. Apparent rim of sclera above the cornea.
3. Lid lag : the upper lid does not follow the
eyeball on looking down.
4. Absence of forehead corrugation on looking
upwards
5. Absence of convergence on looking to anear
object
6. Exophthalmos : A. Apparent exophthalmos B.
True exophthalmos
7. Tremors of the eyelids
Q. What is the pathogenesis of each of these
eye signs ?
A.
# Infrequent blinking, apparent rim of sclera
above the cornea, lid lag and apparent
exophthalmos are all due to upper eyelid
retraction which is caused by spasm of MullerÕs
muscle (thyroxine makes this muscle
oversenstised to the effect of circulating
catecholamines).
# Absence of forehead corrugation is caused by
true exophthalmos.
# Absence of convergence on looking to a near
object is due to paresis of the medial recti.
# True exophthalmos is due to exophthalmos
producing substance which causes deposition of
oedema fluid and round cell infiltration in the
retro-orbital space.
Q. How to differentiate between true &
apparent exophthalmos ?
A. By 1) Naffziger's test; 2) Frazer's test; 3) Ruler
test (See clinical notes for details of these tests)
Q. Define hyperthyroidism and thyrotoxicosis.
A. Hyperthyroidism is the term referred to the
manifestations caused by the increased level of
circulating thyroid hormones. Thyrotoxicosis is a
syndrome consisting of manifestations caused by
the increased level of circulating thyroid hormones
as well as others that are not due to increased
level of circulating thyroid hormones
(Exophthalmos and Pretibial myxoedema).
Q. What are the types of toxic goitre ?
A. There are three types
1) Toxic diffuse goitre (1ry toxic goitre) (Grave's
disease)
2) Toxic nodular goitre (2ry toxic goitre)
(Plummer's disease)
3) Toxic nodule.
Q. Are there other causes of thyrotoxicosis ?
A. Yes. the following are rare causes of
thyrotoxicosis :
1. Thyrotoxicosis factitia : Due to intake of
thyroxine (e.g. for weight reduction)
2. Infantile thyrotoxicosis : A baby born to a
thyrotoxic mother
3. Jod Basedow disease : Due to high intake of
iodides in a colloid goitre
4. De Quervain thyroiditis (in some cases)
5. Hashimoto thyroiditis (in early cases)
6. Some tumours secrete thyroxine e.g. struma
ovarii.
Q. How do you treat a case of toxic nodular
goitre (2ry toxic goitre) ?
A. Subtotal thyroidectomy.
Q. How would you prepare a case of toxic
goitre for operation ?
A. 1. Antithyroid drugs e.g. Neomercazole until
the patient is euthyroid,
2. Propranolol (Inderal) for regulation of heart rate,
3. Lugol's Iodine
Q. When do you contraindicate antithyroid
drugs in preop. preparation ?
A. In retrosternal goitre.
Q. Why ?
A. Because antithyroid drugs cause enlargement
of the thyroid gland which may lead to mediastinal
syndrome.
Q. What is Lugol's iodine ?
A. It is 5% iodine and 10% KI in water.
Q. What is its mechanism of its action ?
A. 1) Inhibition of protease enzyme which releases
thyroid hormones from thyroglobulin,
2) Inhibition of organic iodine formation,
3) Prevention of the stimulant effect of TSH on
adenyl cyclase enzyme.
Q. What is the principle of subtotal
thyroidectomy in toxic goitre ?
A. Subtotal Thyroidectomy = Removal of both
lobes + Isthmus, Leaving postero-medial part of
the lobes on each side to protect the recurrent
laryngeal nerve and parathyroid glands.
Q. What are the complications of subtotal
thyroidectomy for toxic goitre ?
A. 1. Tension haematoma (due to slipped ligature
from the superior thyroid artery).
2. Dyspnoea.
3. Injury to the related nerves : i) recurrent
laryngeal nerve, and ii) external laryngeal nerve .
4. Thyrotoxic crisis.
5. Hypoparathyroidism (due to accidental removal
of the parathyroid glands).
6. Hypothyroidism in 20-30% (if the gland was
removed near totally).
7. Recurrent thyrotoxicosis in 5-10% (If no
adequate excision is done).
Q. What is thyrotoxic crisis ?
A. It is an acute exacerbation of hyperthyroidism.
It occurs if the patient is not adequately prepared
for thyroidectomy.
Q. What are the manifestations of thyrotoxic
crisis ?
A. Hyperpyrexia, restlessness, severe tachycardia,
and dehydration.
Q. Is it a dangerous condition ?
A. Yes it is. Severe tachycardia may lead to heart
failure and hyperpyrexia may lead to brain
damage.
Q.What are the indications of antithyroid
drugs in toxic nodular goitre ?
A.
1. 1. Preoperative preparation.
2. 2. Children and adolescents (high incidence
of recurrence if operated upon).
3. 3. Refusal for surgery.
4. 4. General contraindication for surgery.
Q. Does radio-iodine has a role in the
treatment of toxic nodular goitre ?
A. No, radio-iodine is ineffective in toxic nodular
goitre because of the fibrosis present in the gland.
Q. How do you treat a case of toxic nodule ?
A. Surgery (hemithyroidectomy) is the main line
of treatment. Medical treatment is indicated in
preoperative preparation, in young patients and in
patients refusing surgery or unfit for surgery.
Radio-iodine can be given to patients over 45
years as an alternative to surgery.
Q. What is the mechanism of action of
radioactive iodine in the treatment of toxic
goitre ?
A. Radioactive iodine emits beta rays which
destroys the thyroid cells without affecting much
the surrounding tissue due to their low
penetrability.
Q. What type of radioactive iodine is given in
the treatment of toxic goitre ?
A. I 131.
Q. Why I131 and not I123 ?
A. Because I131 can emit beta rays while I123
can emit only gamma rays which are ineffective.
Q. What is the dose of radioactive iodine in
treatment of toxic goitre ?
A. 10 uCi (10 micro Curi).
Q. What are the disadvantages of radioactive
iodine ?
A. 1. Isotope facilities must be present.
2. Indefinite follow up is essential.
3. Thyroid insufficiency in 80% after 10 years.
4. Recurrence of toxicity if low dose is given.
5. Risk of inducing carcinoma in adults if given in
childhood or adolescence (that is why it is not
given for patients below 45 years).
6. Risk of hypothyroidism and foetal anomalies if
given in pregnancy.
Q. What are the contraindications to radioiodine
?
A. 1. During pregnancy (risk of foetal anomalies
and foetal hypothyroidsm).
2. During lactation (risk of hypothyroidsm to the
baby).
3. Young age (risk of inducing thyroid carcinoma).
4. Toxic nodular goitre (ineffective). 5. Iodine
allergy.
Q. What is the advantage of radio-iodine in a
case of toxic nodule ?
A. No, because the thyroid tissue surrounding the
toxic nodule is suppressed and so will not uptake
iodine.