Flashcards in MEH - Thyroid Dysfunction Deck (27)
Where does the word 'thyroid' come from?
Greek "oval shield"
Should a normal thyroid be felt on examination?
What is the pre-tracheal fascia?
This attaches the thyroid gland to the trachea and larynx, meaning that the thyroid moves upwards on swallowing
Describe briefly the embryology of the thyroid gland
It forms initially under the tongue, and is connected to the skin by the thyroglossal duct. It then moves down past the hyoid bone to in front of the larynx, and the thyroglossal duct closes up
What is a thyroglossal duct cyst?
The thyroglossal duct usually disappears, but it may remain and form a cyst. It will always be in the anterior part of the midline of the neck. When tongue poked out, it will be drawn in
Why can TSH levels be used as an effective screening test for hyper/hypothyroidism?
Very rare for pituitary adenoma to produce TSH and cause thyrotoxicosis, so 98% of metabolic thyroid disease is due to primary abnormality of thyroid gland itself.
What does it suggest about thyroid function if TSH is raised?
Thyroid gland is underfunctioning (hypothyroidism)
What does it suggest about thyroid function if free T4 is increased?
It is over-functioning (hyperthyroidism)
Why is there a wide range of acceptable values for TRH, TSH and T4?
They are constantly responding to the environment
Are autoimmune endocrine diseases more common in women or men?
Women - we don't know why
What are the three goitre structures?
- single nodule
Give three points in a woman's life at which physiological goitre may occur
How does iodine deficiency cause goitre?
Reduced thyroxine levels lead to increased TSH, which causes generalised thyroid enlargement, usually nodular
What is multinodular goitre?
Condition of unknown cause which affects 5% of western populations. Normal thyroid function at first, although after many years some may develop hyperthyroidism
What would be the symptoms in a child with iodine deficiency?
- intellectual disability
- abnormal gait
- short stature
What is a retrosternal multinodular goitre?
A multinodular goitre may enlarge inferiorly into the superior mediastinum to form a retrosternal goitre. This can cause tracheal compression
What is myxoedema?
Non-pitting oedema due to deposition of mucopolysaccharides around eyes, hands and feet.
What can cause hypothyroidism?
- autoimmune destruction of the thyroid (Hashimoto's disease)
- severe iodine deficiency
- post-surgical removal of the thyroid
How is hypothyroidism treated?
Give some clinical signs of thyrotoxicosis
- weight loss
- warm, sweaty hands
- fine hand tremor
- tachycardia/atrial fibrillation
- bounding pulse
- proximal myopathy
- lid lag
- staring eyes
Why do staring eyes occur in thyrotoxicosis?
The levator palpebrae superioris muscle is 90% skeletal muscle and 10% smooth muscle - this smooth muscle is supplied by the sympathetic nervous system. Over stimulation of this leads to staring eyes and lid lag
Give some causes of thyrotoxicosis due to hyperthyroidism
- Graves' disease
- toxic multinodular goitre
- toxic adenoma
What is Graves' disease?
An autoimmune condition affecting the thyroid. Thyroid stimulating immunoglobulin (TSI) attaches to and stimulates the TSH receptor. This causes symptoms of thyrotoxicosis with additional symptoms of exophthalmos and pre-tibial myxoedema
How is thyrotoxicosis treated?
- carbimazole, which prevents thyroid peroxidase coupling and iodinating the tyrosine residues on thyroglobulin, reducing production of T4
- surgical excision of thyroid
- ablative dose of radioactive iodine
How do thyroid cancer present?
As a thyroid nodule - they do not cause either hyper- or hypothyroidism
Which conditions can cause goitre but no metabolic dysfunction?
- multinodular goitre
- iodine deficiency
- thyroid cancer