The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
1
The thyroid gland
Thyroid lump or thyroid swelling or goitre
It is a common thyroid problem, affecting about 5% of the population that
presents as a lump in the neck or sometimes presents with an acute painful
enlargement. It can be divided to 3 main types:
1- Diffuse goiter.
2- Multinodular goitre.
3- Solitary nodule.
1-
Diffuse goitre
A- Simple goitre
This form of goitre usually presents between the ages of 15 and 25 years
It occurs sporadically and is of unknown aetiology.
The goitre is soft and symmetrical and the thyroid is enlarged to two or three
times its normal size.
There is no tenderness, overlying bruit, and lymphadenopathy.
T3, T4, and TSH are normal and no thyroid autoantibodies are detected.
A diffuse goitre rarely needs further treatment and in most cases the goitre
regresses unless it is very large and causing cosmetic symptoms or
compression of other local structures (resulting in stridor or dysphagia).
Thyroxine therapy is sometimes justified in an attempt to shrink the goitre.
In some, however, the unknown stimulus to thyroid enlargement persists and,
as a result of recurrent episodes of hyperplasia and involution during the
following 10–20 years, the gland becomes multinodular with areas of
autonomous function (Multinodular goitre).
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
2
B- Hashimoto’s thyroiditis
Thyroiditis refers to an inflammation of the thyroid.
Hashimoto’s thyroiditis is characterised by destructive lymphoid infiltration
of the thyroid, leading to a varying degree of fibrosis and thyroid
enlargement.
Hashimoto’s thyroiditis increases in incidence with age and affects more
women than men.
Many present with a moderately sized diffuse goitre, which is
characteristically
firm or rubbery in consistency. It is sometimes impossible
to differentiate it from simple goitre by palpation alone. Around 25% of
patients are hypothyroid at presentation, the others are normal, but these
patients are at risk of developing overt hypothyroidism in future years.
Anti-thyroid peroxidase antibodies are present in the serum in more than
90% of patients with Hashimoto’s thyroiditis. Thyroxine therapy is indicated
as a treatment for hypothyroidism, and also to shrink an associated goitre.
Although rare, there is an increased risk of thyroid lymphoma.
Spontaneous atrophic hypothyroidism, a term used for hypothyroid patients
without a goitre in whom TSH receptor-blocking antibodies may be more
important than anti-peroxidase antibodies.
However, these syndromes can both be considered as variants of the same
underlying disease process, and sometimes are given the nomenclature of
autoimmune hypothyroidism.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
3
C- Transient thyroiditis
I. Subacute (de Quervain’s) thyroiditis
- It is a transient inflammation of the thyroid gland occurring after
infection with Coxsackie, mumps or adenoviruses.
- There is pain in the region of the thyroid that radiates to the jaw, the ears,
and is made worse by swallowing, coughing and movement of the neck.
- The thyroid is usually palpably enlarged and tender.
- Systemic upset is common.
- Affected patients are usually females aged 20–40 years.
II. Silent thyroiditis
Is another form of Subacute but Painless transient thyroiditis, also
occur after viral infection and in patients with underlying autoimmune
disease.
III. Drug-induced thyroiditis
- The condition can also be precipitated by drugs, including amiodarone,
interferon-α, and lithium. Symptoms continue as long as the drug is taken.
In all these forms, inflammation in the thyroid gland occurs and is
associated with release of colloid and stored thyroid hormones, with damage to
follicular cells and impaired synthesis of new thyroid hormones. As a result, T4
and T3 levels are raised for 4–6 weeks until the preformed colloid is depleted.
Thereafter, there is usually a period of hypothyroidism of variable severity until
follicular cells recover and normal thyroid function is restored within 4–6
months. During this time there is negligible radioisotope uptake, because the
damaged follicular cells are unable to trap iodine and because TSH secretion is
suppressed.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
4
Low-titre thyroid autoantibodies appear transiently in the serum, and the
ESR is usually raised.
The pain if present usually responds to (NSAIDs).
Occasionally, it may be necessary to prescribe prednisolone 40 mg daily for 3–4
weeks. The thyrotoxicosis is mild and treatment with a β-blocker is usually
adequate. Antithyroid drugs are of no benefit because thyroid hormone synthesis
is impaired rather than enhanced. Thyroxine can be prescribed temporarily in
the hypothyroid phase.
IV. Acute thyroiditis (also called suppurative thyroiditis)
- Caused by bacteria. Symptoms include a painful thyroid, generalized
illness, and occasionally symptoms of mild hypothyroidism.
- Symptoms improve after treatment of the infectious cause.
V. Post-partum thyroiditis
- The maternal immune response, which is depressed during pregnancy to
allow survival of the fetus, is enhanced after delivery and may unmask
previously unrecognized subclinical autoimmune thyroid disease.
- Symptoms of thyroid dysfunction
are rare. However, symptomatic
thyrotoxicosis presenting
for the first time within 12 months of childbirth
is likely to be due to post-partum thyroiditis and the diagnosis is
confirmed by a negligible radioisotope uptake.
- The clinical course and treatment are similar to painless subacute
thyroiditis.
- Post-partum thyroiditis tends to recur after subsequent pregnancies and
eventually patients progress over a period of years to permanent
hypothyroidism.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
5
D- Iodine-associated thyroid disease
I. Iodine deficiency
Thyroid enlargement is extremely common in certain mountainous parts of the
world, where there is dietary iodine deficiency (endemic goitre). Most patients are
euthyroid with normal or raised TSH levels, although hypothyroidism can occur
with severe iodine deficiency.
Iodine supplementation programmes have abolished this condition in most
developed countries.
II. Iodine-excess thyroid dysfunction
Iodine has complex effects on thyroid function.
1- Very high concentrations for short periods, iodine inhibit thyroid hormone
release (as in iodine treatment of thyroid storm and prior to subtotal
thyroidectomy).
2- Lower concentrations of iodine effects varies according to whether the patient
Iodine-deficient diet, or
Underlying thyroid disease, or
Duration.
In iodine-deficient parts of the world, transient thyrotoxicosis may be
precipitated by prophylactic iodinsation programmes.
In iodine sufficient areas, thyrotoxicosis can be precipitated by Iodine-excess
in individuals who have underlying thyroid disease predisposing to thyrotoxicosis,
such as multinodular goitre or Graves’ disease in remission.
Induction of thyrotoxicosis by iodine is called the Jod–Basedow effect.
Chronic excess iodine administration can, however, result in hypothyroidism.
Increased iodine within the thyroid gland down-regulates iodine trapping, so
that uptake is low in all circumstances.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
6
Amiodarone
The anti-arrhythmic agent amiodarone affect the thyroid by:
Has a structure that is analogous to T4.
Contains huge amounts of iodine.
Cytotoxic effect on thyroid follicular cells.
Inhibits conversion of T4 to T3.
Only 20% of patients receiving amiodarone develop hypothyroidism or
thyrotoxicosis and so thyroid function should be monitored regularly.
The thyrotoxicosis can be classified as either:
Type I: a Jod–Basedow effect in patients with underlying thyroid disease, or
Type II: thyroiditis due to cytotoxicity, resulting in a transient thyrotoxicosis.
These patterns can overlap and can be difficult to distinguish.
There is no widely accepted management algorithm. Antithyroid drugs may be
effective in type I form. Prednisolone is beneficial in type II form. Potassium
perchlorate can also be used to inhibit iodine trapping in the thyroid. If the cardiac
state allows, amiodarone should be discontinued.
2-
Multinodular goitre
Patients with diffuse thyroid enlargement in the absence of thyroid
dysfunction or positive autoantibodies (i.e. ‘simple goitre’) may progress to
develop nodules. These nodules grow at varying rates and start to secrete
thyroid hormone ‘autonomously’, thereby suppressing TSH-dependent growth
and function in the rest of the gland. Ultimately, complete suppression of TSH
occurs in about 25% of cases leading to (toxic multinodular goitre).
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
7
There are reports that the prevalence of foci of thyroid cancer is increased
in multinodular goitres, but for practical purposes patients can be reassured
that it is a benign condition and malignancy need only be considered in
patients with a large ‘dominant’ nodule that is ‘cold’ (i.e. does not take up
radioisotope).
Diffuse and multinodular goitre has a 1:20 chance of malignancy.
Clinical features and investigations
Multinodular goitre presents with either:
Thyrotoxicosis, or
Large goiter, or
Sudden painful swelling caused by haemorrhage into a nodule or cyst.
Very large goitres may cause mediastinal compression with stridor,
dysphagia and obstruction of the superior vena cava. Hoarseness due to recurrent
laryngeal nerve palsy can occur, but is far more suggestive of thyroid carcinoma.
The diagnosis can be confirmed by a radioisotope thyroid scan and/ or
ultrasonography.
In those with a ‘dominant’, ‘cold’ nodule, fine needle aspiration is indicated to
exclude thyroid cancer.
Management
If the goitre is small and nontoxic, no treatment is necessary, but follow up.
Partial thyroidectomy is indicated for large goitres, or
131
I for the old.
Thyroxine therapy is of no benefit in shrinking multinodular goitres.
In toxic multinodular goitre treatment is usually with
131
I.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
8
3-
Solitary thyroid nodule
It is important to determine whether the nodule is benign or malignant. It is
rarely possible to make this distinction on clinical grounds alone, although the
presence of:
Cervical lymphadenopathy.
Presenting in childhood / adolescence.
Past history of head and neck irradiation.
Presenting in the elderly.
Very occasionally, a secondary deposit from a renal, breast, or lung
carcinoma presents as a painful, rapidly growing solitary thyroid nodule.
Investigations
o Regarding serum T3, T4 and TSH, the finding of undetectable TSH is very
suggestive of a benign autonomously functioning thyroid follicular
adenoma.
o For euthyroid patients, the most useful investigation is FNA of the nodule.
o Cytological examination can differentiate benign (80%) from definitely
malignant or indeterminate nodules (20%), of which 25–50% are confirmed
as cancer at surgery.
Management
Solitary nodules with a solid component in which cytology either is
inconclusive or shows malignant cells are treated by surgical excision.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
9
Thyroid malignancy
Primary thyroid malignancy is rare, accounting for less than 1% of all
carcinomas,
With the exception of medullary carcinoma, thyroid cancer is more common in
females.
Papillary carcinoma
This is the most common of the malignant thyroid tumours and accounts for
90% of irradiation-induced thyroid cancer.
It may spread is to regional lymph nodes.
Follicular carcinoma
This is always a single encapsulated lesion.
Rare metastases to LN because metastases are blood-borne and are most
often found in bone, lungs and brain.
Management for both
This is usually by total thyroidectomy followed by a large dose of 131I to
ablate any remaining thyroid tissue, normal or malignant.
Thereafter, long-term treatment with thyroxine in a dose sufficient to
suppress TSH (usually 150–200 μg daily) is important, as there is evidence
that growth of differentiated thyroid carcinomas is TSH-dependent.
Follow up is by measurement of serum thyroglobulin, which should be
undetectable in patients whose thyroid has been ablated and who are taking
a suppressive dose of thyroxine.
Prognosis
Most patients have an excellent prognosis when treated appropriately.
The thyroid gland - Dr. Omar Al- Azzawy
Part 3
3-3-2016
10
Medullary carcinoma
This tumour arises from the parafollicular C cells.
In addition to calcitonin, the tumour may secrete 5-hydroxytryptamine (5-HT,
serotonin), tachykinin peptides, ACTH and prostaglandins. As a consequence,
carcinoid syndrome and Cushing’s syndrome may occur.
Patients usually present in middle age with a firm thyroid mass.
Cervical lymphadenopathy involvement is common, but distant metastases
are rare initially.
Serum calcitonin levels are raised and are useful in monitoring response to
treatment.
Treatment is by total thyroidectomy. Since the C cells do not concentrate
iodine, there is no role for I
131
therapy.
Medullary carcinoma of the thyroid may occur sporadically, or in families as
part of the MEN type 2 syndrome.
Riedel’s thyroiditis
This is not a form of thyroid cancer, but the presentation is similar and the
differentiation can usually only be made by thyroid biopsy.
It is a very rare condition of unknown aetiology in which there is extensive
infiltration of the thyroid and surrounding structures with fibrous tissue.
There may be associated mediastinal and retroperitoneal fibrosis.
Presentation is with a slow-growing goitre which is irregular and stony-hard.
There is usually tracheal and oesophageal compression.
Other recognised complications include recurrent laryngeal nerve palsy,
hypoparathyroidism and eventually hypothyroidism.
… END …