Pathology of the thyroid 1
Dr: Salah Ahmed
- diseases of the thyroid include:
1- conditions associated with excessive release of thyroid hormones (hyperthyroidism
2- conditions associated with thyroid hormone deficiency (hypothyroidism)
3- mass lesions
- thyroid diseases: 1- thyroiditis
2- Graves disease (PBL)
3- Goiter (case discussion)
4- tumors
- first we talk about the clinical consequences of disturbed thyroid function (hyperand hypothyroidism) then we focus on the disorders that generate these problems
Normal thyroid tissue
Hyperthyroidism
- Thyrotoxicosis: hypermetabolic state caused by elevated circulating levels of free T3 and
T4
- referred to hyperthyroidism because it is caused most commonly by hyperfunction of the
thyroid gland
- Causes: 1- those associated with hyperthyroidism
a) primary
i- diffuse toxic hyperplasia (Graves disease)
ii- hyperfunctioning ("toxic") multinodular goiter
iii- hyperfunctioning ("toxic") adenoma
b) secondary
i- TSH-secreting pituitary adenoma (rare)
2- those not associated with hyperthyroidism
i- subacute granulomatous thyroiditis (painful)
ii- subacute lymphocytic thyroiditis (painless)
iii- struma ovarii (ovarian teratoma with thyroid)
iv- exogenous thyroxine intake
- Clinical manifestations: - include changes referred to the hypermetabolic state and
overactivity of the sympathetic nervous system:
1- Constitutional symptoms: - skin: soft, warm (vasodilatation, increased flow
-heat intolerance and excessive sweating are common (hypermetabolism
- weight loss despite increased appetite( increased muscle protein
catabolism)
2- Gastrointestinal:- hypermotility, malabsorption, and diarrhea (stimulation of gut)
3- Cardiac: palpitations and tachycardia are common (B adrenorgenic receptors,
catecholamine) elderly patients may develop congestive heart failure (aggravation of
preexisting heart disease)
4- Neuromuscular:- overactivity of sympathetic produces tremor, hyperactivity,
anxiety, irritability and nervousness . Nearly 50% develop muscle weakness (thyroid
myopathy).
5- Ocular manifestations: a wide, staring gaze and lid lag (sympathetic
overstimulation of the levator palpebrae superioris ), associated with proptosis
(exophthalmos) in Graves due to: 1- marked infiltration of the retro-orbital space by
mononuclear cells ( T cells)
2- inflammatory edema
3- accumulation hydrophilic glycosaminoglycans such as
hyaluronic acid and chondroitin sulfate
4-fatty infiltration
6- Thyroid storm: - used to designate the abrupt onset of severe hyperthyroidism
- occurs commonly in Graves disease
- results from acute elevation in catecholamine levels:
1- infection 2- surgery 3- stress 4- cessation of treatment
- patients often febrile and present with tachycardia
- it is a medical emergency
- most patients die of cardiac arrhythmias
7- Apathetic hyperthyroidism: thyrotoxicosis occurring in the elderly, in whom old age
and various co-diseases may blunt the typical features of thyroid hormone excess seen
in younger patients.
Ocular manifestation: wide, staring gaze and lid lag
- Diagnosis:
is based on clinical features and laboratory data
1- measurement of serum TSH concentration (decreased, in rare cases of
secondary hyperthyroidism, TSH levels are either normal or raised)
2- free thyroid hormone assay: increased levels of free T4, occasionally T3 (T3
toxicosis)
3- measurement of radioactive iodine uptake by the thyroid gland: useful in
determining the etiology. For example
i- diffuse increased uptake (Graves disease)
ii- increased uptake in a solitary nodule (toxic adenoma)
iii- decreased uptake (thyroiditis).
Hypothyroidism
- is caused by any structural or functional derangement that interferes with the
production of thyroid hormone.
- either primary (thyroid abnormality) or secondary ( hypothalamic or pituitary
disease)
- causes: 1- Primary
1- surgery, radioiodine therapy, or external radiation
2- Hashimoto thyroiditis
3- iodine deficiency
4- inborn error of metabolism (enzyme deficiency)
5- drugs (lithium, iodides, p- aminosalicylic acid)
6- rare developmental abnormalities of the thyroid (thyroid dysgenesis)
2- Secondary
1- Pituitary or hypothalamic failure (uncommon)
- Clinical manifestations: - two forms: 1- cretinism 2- myxedema
1- Cretinism: - hypothyroidism developing in infancy or early childhood
- common in areas of endemic dietary iodine deficiency (Himalayas,
China, Africa, and other mountainous areas)
- now becomes less frequent because of the widespread
supplementation of foods with iodine
- rarely cretinism may also result from inborn errors in metabolism
(e.g., enzyme deficiencies)
- Clinical features: impaired development of the skeletal system and
central nervous system with severe mental retardation, short stature,
coarse facial features, a protruding tongue, and umbilical hernia
2- Myxedema: - hypothyroidism developing in older children and adults (Gull
disease)
- Manifestations: 1- generalized fatigue, apathy
2- patients are cold intolerant, and often obese
3- mucopolysaccharide -rich edema accumulates in
skin, subcutaneous tissue, and number of visceral sites,
with broadening and coarsening of facial features,
enlargement of the tongue, and deepening of the voice
iv- Bowel motility is decreased, resulting in constipation
v- shortness of breath and decreased exercise capacity
(reduced cardiac output)
vi- pericardial effusions are common; in later stages the
heart is enlarged, and heart failure may supervene.
- Laboratory diagnosis:
- Measurement of the serum TSH is the most sensitive screening test
(increased in primary, not increased in secondary hypothyroidism)
- Serum T4 is decreased
Cretinism
Thank you