Primary and Secondary Hypothyroidism Flashcards
(11 cards)
What is primary hypothyroidism?
- Very common endocrine disease seen in herbalism practice
- Associated with a deficiency of
thyroid hormones - thyroid gland itself does not create enough hormones - Decreased production of T4 causes
an increase in the secretion of TSH
by the pituitary gland - pituitary is saying ‘come on!!’ - When TSH created in large quantities this stimulates hypertrophy and
hyperplasia of the thyroid gland - they thyroid gland gets bigger. The body hopes this will help but this can cause a goitre and press on surrounding structures.
What are the signs and symptons of hypothyroidism?
Very numerous, and non specific - not present in every case
e.g.
* Fatigue
* Depression
* Poor concentration
* Weight gain
* Constipation
* Intolerance of cold
* Sleep apnoea
* Menstrual irregularities
* Sexual dysfunction
* Subfertility
* Oedema
* Carpal tunnel syndrome
* Muscle and/or joint pain
* Dull facial expression
* Drooping eyelids
* Puffy face
* Periorbital Oedema
* Dry or thinning hair
* Dry or coarse skin
* Bradycardia
* Slow speech
* Hoarse voice
* Goitre
* Macroglossia
* Thinning/loss of outer eyebrow
* Non-pitting pretibial oedema
* Hyporeflexia
What causes hypothyroidism?
- Autoimmune disease (Hashimoto’s thyroiditis) - most common cause in iodine sufficient countries
- Iodine deficiency - most common cause worldwide
- Congenital hypothyroidism - born this way
- Post partum - underactive after giving birth
- Medical or surgical treatment for Hyperthyroidism - if someone has an overactive thryoid the treatment can cause perm damage which then results in hypothryroidism
- Radiation treatment to the neck
What is Hashitmoto’s disease?
- Most common cause of hypothyroidism in iodine sufficient countries, but common condition generally
- Autoimmune disease associated with lymphocytic infiltration of the thyroid gland - white blood cells get into the thyroid gland
- Destruction of thyroid cells by anti-thyroperoxidase (anti-TPO) antibodies
- In the early stages as cells are destroyed, T4 & T3 may be released into the circulation due to cell damage, causing transient hyperthyroidism
- However, ultimately, autoimmune destruction of the thyroid gland results in insufficient production of thyroid hormones
- Wide range of effects due to deficiency of thyroid hormone, resulting derangements
in metabolic processes, & myxedematous infiltration
What is postpartum hypothyroidism?
- Also where white blood cells attack the thyroid
- Lymphocytic thyroiditis affects up to 10% of postpartum women
- Affects up to 25% of post-partum women with type 1 diabetes mellitus) up to 12 months after delivery.
- Frequently transient, resolving within 12 months
- Increased risk for recurrence of postpartum thyroiditis with future pregnancies or permanent hypothyroidism.
What are the other causes of hypothyroidism?
- Prior treatment for a past thyroid conditions or cancer which damage the thyroid gland (radioactive iodine, thyroidectomy or radiation for head and neck cancers)
- Also, people who take drugs which decrease thyroid hormone secretions e.g. amiodarone, lithium, anticonvulsants, certain chemotherapy drugs, or drugs affecting the immune system such as interferon alpha or Tyrosine kinase Inhibitors (TKIs)
What are the risk factors for hypothyroidism?
- Family history of thyroid disease.
- History of other autoimmune conditions (e.g. pernicious anaemia, coeliac disease, type 1 diabetes, SLE, rheumatoid arthritis, Sjögren’s syndrome.
- History of other conditions (e.g. primary adrenal insufficiency, Turner syndrome).
- Pregnancy and post-partum
- Vitamin D deficiency
- Use of certain medications (e.g. amiodarone, lithium, anticonvulsants, certain chemotherapy drugs, and drugs affecting the immune system such as TKIs).
- Prior treatment for thyroid conditions or cancer (radioactive iodine, thyroidectomy or radiation for head and neck cancers).
- Dietary iodine deficiency or excess.
- Being assigned female at birth (ratio approximately 1:10)
- Incidence of all cause hypothyroid increases with age especially in those over 60
(30-50 for Hashimoto’s in AFAB, 40-60 for AMAB)
What are the conventional tests and investigations for hypothyroidism?
Observation (signs):
* Dull facial expression, drooping eyelids, puffy eyes or face
* Dry or thinning hair, dry or coarse skin - have they noticed this themselves?
* Thinning or loss of the outer corner of the eyebrows
* Non-pitting oedema- press your thumb in and it leaves no indentation/ bounces back
* Slow speech, hoarse voice, macroglossia (tongue seems larger than normal)
* Scar from previous thyroidectomy
Other examinations to identify signs such as:
* Goitre or thyroid nodules
* Bradycardia - slow heart rate
* Diastolic hypertension
* Narrow pulse pressure - smaller difference between the two blood pressures
* Hyporeflexi - reflexes is slower than you would expect
Specific blood tests
* Suboptimal levels of T4 and T3
* Elevated levels of TSH (low levels of thyroid hormones trigger the pituitary gland to increase TSH)
* In euthyroid sick syndrome (due to severe, acute illness) the free T3 is reduced,
Reverse T3 may be raised, and TSH and T4 may be normal.
* So it is essential to measure TSH, T4, and T3 in patients with symptoms of
underactive thyroid, as sometimes its tricky to spot. Restrictions in blood tests may mean things are missed at diagnosis, and only TSH is measured.
* Biotin supplements may interfere with the accuracy of hormones assays. (Discontinue supplements containing biotin for 2-3 days before testing).
Antibody tests are also useful for suspected hypothyroidism
* Anti-TPO (anti-thyroid peroxidase)
* Anti-Tg (anti-thyroglobulin) antibodies
* TSH receptor-blocking antibodies (TBII)
Antibodies are only present only in hypothyroidism caused by autoimmune thyroiditis (10-15% of patients with
Hashimoto’s thyroiditis may be antibody negative).
Hypothyroidism may also associated with:
* Hyperlipidaemia (raised cholesterol and triglycerides)
* Anaemia (low red blood cell count due to reduced erythropoiesis)
* Low ferritin (due to the effect of reduced thyroid hormones on ferritin synthesis)
* Hyponatraemia (is low sodium, which in this case is due to excess fluid in the blood diluting sodium levels)
* Hyperprolactinaemia (due to elevated TRH levels)
* Low sex hormone binding globulin (due to effect of hypothyroidism on oestrogen levels)
Further investigations
* Ultrasound to identify if nodules on the thyroid gland are present.
* Fine needle aspiration of suspicious nodules to exclude malignancy
What are potential complications of hypothyroidism?
Hypothyroidism is associated with increased risk of the following, many of which are linked to changes in metabolism
* Insulin resistance
* Chronic kidney disease
* Coronary artery disease
* Thyroid cancer
* Heart failure (without treatment)
* Myxedema coma or death (without treatment)
* Severe mental retardation in children (without treatment).
Good prognosis with treatment. Symptoms usually reverse within in a few weeks.
What are the effects on pregnancy and neo-natal outcomes? Sub fertility
* Decreased production of T3 and/or T4 by the thyroid gland results in elevated TRH, due to reduced negative feedback on the hypothalamus.
* Elevated TRH increases prolactin release from the pituitary.
* Elevated prolactin in turn causes suppression of GnRH by the hypothalamus, resulting in low pituitary secretion of FSH.
* Lack of stimulation of ovarian follicles by FSH leads to low levels of oestrogen, and prevents normal follicular growth and maturation, leading to sub-fertility
In pregnant people, hypothyroidism, subclinical hypothyroidism (TSH raised by nothing else) and autoimmune thyroid disease without overt hypothyroidism can also increase the risk of:
* Infertility
* Pregnancy complications such as anaemia, preeclampsia, post-partum haemorrhage
* Low birth weight, and
* Impaired cognitive development in the offspring
What is secondary hypothyroidism?
Secondary hypothyroidism is not due to a problem with the thyroid itself, but to a
problem with the pituitary gland or hypothalamus, such as:
- Genetic TRH resistance or deficiency
- Pituitary or hypothalamic tumours which compress normal TRH/TSH-producing
cells, so inadequate secretion of hormones - Radiation therapy to the brain which can damage the hypothalamus or pituitary
- Drugs (such as dopamine, prednisone and opioids) which reduce TSH secretion.
Suboptimal levels of T3 and T4 are associated with low TSH: the thyroid gland receives
insufficient stimulation from pituitary thyrotropin hormones, and the hypothalamus or pituitary fails to respond to the resulting low thyroid hormone levels.
What is euthyroid sick syndrome?
* May be due to any severe, acute illness.
* Free T3 is reduced, but TSH and T4 may be normal.
* It is therefore essential to measure TSH, T4, and T3 in patients with symptoms of underactive thyroid.
What is convential treatment for hypothyroidism?
- Conventional treatment for all types of hypothyroidism is thyroid hormone
replacement (levothyroxine). - In some (rare) cases, T3 may be prescribed in combination with T4
- Surgery is not usually indicated for hypothyroidism except in the case of a large goitre with obstructive symptoms, presence of a malignant nodule or lymphoma.
- In pregnant people with hypothyroidism, the dose of medication usually needs to be
increased
