Hypothyroidism Flashcards
What is hypothyroidism?
Insufficient production of thyroid hormones, leading to metabolic slowdown
What head and neck features are seen in hypothyroidism?
(1) Macroglossia
= tongue is abnormally large compared to the mouth
(2) Puffy face
(3) Possible goitre
(depending on the cause)
What are the peripheral features of hypothyroidism?
(1) Dry, thick skin
(2) Brittle hair
(3) Scanty secondary sexual hair
(4) Queen Anne’s sign
(loss of outer 1/3 of eyebrows)
(5) Cold intolerance
What are the cardiac manifestations of hypothyroidism?
Bradycardia and cardiomegaly
How does hypothyroidism affect the nervous system?
(1) Carpal tunnel syndrome
(2) Slow relaxing reflexes
(3) Cerebellar ataxia
(4) Peripheral neuropathy
(5) Difficulty concentrating
What are the menstrual abnormalities in hypothyroidism?
Menorrhagia
(heavy menstrual bleeding)
What bedside test findings might suggest hypothyroidism?
(1) Bradycardia
(2) Goitre
(3) Dry skin
(4) Loss of outer 1/3 of the eyebrows
What blood tests are used to diagnose hypothyroidism?
(1) Thyroid function tests (TFTs)
= Raised TSH and low T3/T4
(2) Antibody testing
= Anti-TPO, Anti-thyroglobulin, Anti-TSH receptor
(to check for autoimmune causes)
(3) Iodine levels
= To determine if deficiency or excess is a factor
What imaging studies are used for hypothyroidism?
- Ultrasound scan (USS) of the neck
- Thyroid biopsy - not done unless necessarily
What is the primary treatment for hypothyroidism?
Levothyroxine (LT4) replacement therapy
How often should TSH levels be monitored in non-pregnant patients?
Every 3 months initially, then annually once stable
What specialist referral is required for hypothyroidism?
All patients with overt or subclinical hypothyroidism should be followed up by an endocrinology specialist
How does pregnancy affect levothyroxine dosing?
The dose is usually increased by 25-50 mcg due to increased metabolic demands
When should TFTs be checked during pregnancy?
Immediately upon confirmation of pregnancy, and results should be interpreted using the pregnancy-specific reference range
What are the foetal/neonatal complications of hypothyroidism?
(1) Low birth weight & growth restriction
(2) Neurodevelopmental delay
(3) Congenital hypothyroidism
= if iodine deficiency or maternal autoantibodies are present
When should TFTs - thyroid function tests be checked before conception?
Before attempting pregnancy, ensure the patient is in a euthyroid range.
If abnormal, conception should be delayed until TSH stabilises with levothyroxine treatment
What do thyroid function tests include?
TSH (Thyroid-Stimulating Hormone)
= (1) Elevated in primary hypothyroidism
(2) Low in secondary hypothyroidism
Free T4 (Thyroxine)
(1) Low in hypothyroidism
Free T3 (Triiodothyronine)
(1) May be low or normal in hypothyroidism
What are the bone complications of an early menopause?
Osteoporosis
What are the most common causes of hypothyroidism?
(1) Autoimmune thyroiditis =Hashimoto’s
(2) Iodine deficiency
(3) Post-thyroidectomy
(4) Congenital hypothyroidism, and certain medications (eg, lithium, amiodarone)
What is the most common cause of hypothyroidism worldwide?
Iodine deficiency
What does the loss of the lateral third of the eyebrow relate to?
Hashimoto’s thyroiditis
= Queen Anne’s sign
A 68-year-old woman is brought to the emergency department after being found unresponsive at home. She has a background of osteoarthritis, hypothyroidism, hypertension, depression and vascular dementia. Her regular medications include paracetamol, codeine, levothyroxine, ramipril, sertraline and amlodipine. Her family have expressed concerns about her adherence to medications because of a decline in her memory.
The patient’s observations are: temperature 33.2°C, HR 42, BP 106/64, RR 12, oxygen saturations 96% on air. On examination, she is unresponsive. Periorbital oedema is noted. She has bibasal lung crackles and pitting oedema to the ankles. Blood results are pending.
What is the best next step in management?
IV hydrocortisone or IV levothyroxine
When is Tinel’s sign positive?
When tapping over a nerve causes tingling, pain, or paresthesia in its distribution
Difficulty concentrating, hair loss and joint pain are all associated with what disease?
Hypothyroidism
What are the TSH, Free T4, and T3 levels in primary hypothyroidism
eg, Hashimoto’s Thyroiditis?
TSH: Elevated
Free T4: Low
T3: Low or normal
What are the TSH, Free T4, and T3 levels in secondary hypothyroidism?
TSH: Low or normal
Free T4: Low
T3: Low
What are the TSH, Free T4, and T3 levels in subclinical hypothyroidism?
TSH: Elevated (mild increase)
Free T4: Normal
T3: Normal
What are the normal levels for TSH?
0.4–4.0 mU/L
What are the normal levels for Free T4?
10–26 pmol/L
What are the normal levels for T3?
1.5–3.1 nmol/L
A 38-year-old woman presents with fatigue, weight gain and cold intolerance. She also reports constipation and dry skin. On examination, her skin is cool to the touch and her reflexes are slow.
What laboratory finding would most likely confirm the diagnosis suggested by her presentation?
Increased thyroid-stimulating hormone (TSH) levels
What is the half life of TSH?
4-6 weeks
A 50-year-old with well-controlled hypothyroidism has recently started a new medication. You repeat her TFTs and this shows she now has under treated disease. She has had recent symptoms of increased tiredness, palpitations and breathlessness with a low MCV on blood tests. You are worried this new medication may be affecting the absorption of levothyroxine
What medications have likely caused this?
(1) Calcium chloride
(2) Digoxin
(3) Hormone Replacement Therapy
(4) Ferrous Sulphate
A classical sign of poor compliance/ adherence to levothyroxine is what?
normal free T4 but elevated TSH
A 55-year-old woman presents to her GP with lethargy and weight gain. Blood tests lead to a diagnosis of hypothyroidism. She attends her GP to discuss treatment options, including levothyroxine.
Which of the following side effects of levothyroxine should she be counselled on?
A. Weight gain
B. Hair loss
C. Hypoglycaemia
D. Osteoporosis
E. Headache
D
What is the recommended starting dose of levothyroxine for severe hypothyroidism or patients over 50 years old?
25 mcg once daily, with the dose slowly titrated
What is the recommended starting dose of levothyroxine for other patients with hypothyroidism?
50 mcg once daily
When should levothyroxine be increased during pregnancy?
Levothyroxine should be increased by 25 mcg as soon as pregnancy is confirmed, even if the patient is euthyroid
Why is levothyroxine increased during pregnancy?
Pregnancy causes a natural increase in free thyroxine to support the foetus until the 12th week.
Untreated hypothyroidism can lead to neurodevelopmental delays, so the dose is increased to mimic this surge and protect the foetus
The heel prick test is taken when?
at 5-8 days of life
Children with auto-immune thyroiditis are at higher risk of developing other auto-immune mediated conditions, such as what?
(1) Type 1 diabetes
(2) RA
(3) Vitiligo
Which antibody is most associated with Hashimoto’s thyroiditis - an autoimmune cause of hypothyroidism?
Anti-TPO antibodies
= Thyroid-stimulating hormone receptor antibodies are most assocaited with Grave’s Disease
How does thyroid function affect weight?
Hypothyroidism causes weight gain, while hyperthyroidism leads to weight loss
Which medications should be taken at least 4 hours apart from levothyroxine? and why?
Iron supplements, calcium carbonate, and antacids
= to avoid reduced absorption
What is Myxoedemic coma and how is it treated?
Potentially fatal complication of undiagnosed hypothyroidism or poor adherence to levothyroxine therapy
which leads to : normal free T4 but elevated TSH
= thyroxine and hydrocortisone
Why does TSH remain high in those who have a poor adherence to levothyroxine therapy?
the pituitary senses a need for more thyroid hormone
A 45-year-old woman attends a follow-up appointment having been diagnosed with Hashimoto’s thyroiditis and started on levothyroxine. She asks about associated conditions, as she has heard that Hashimoto’s thyroiditis is linked to certain cancers.
What cancer should you inform her that she is at increased risk of developing?
MALT lymphoma
A 43-year-old woman presents for a follow-up in the clinic. She was diagnosed with Hashimoto’s thyroiditis four months ago and is currently being treated with levothyroxine 75 mcg od. What is the most important blood test to assess her response to treatment?
TSH
“Hypothermia, hyporeflexia, bradycardia and seizures”
These symptoms suggest what?
Myxoedemic coma
