hypothyroidism Flashcards
What is hypothyroidism?
Clinical syndrome resulting from insufficiency secretion of thyroid hormones (T3/T4) from the thyroid gland
What are the causes of hypothyroidism?
- PRIMARY HYPOTHYROIDISM/ MYXOEDEMA (decreased thyroid hormone production)
*Acquired “SAIDIT”
- Severe iodine deficiency - MOST COMMON worldwide
- Autoimmune: Hashimoto’s thyroiditis MOST COMMON
- Iatrogenic (post-surgery, radioiodine, hyperthyroid medication)
- Drug induced: antithyroid drugs, amiodarone, lithium, iodine
- Infiltrative disorders e.g. amyloidosis, sarcoidosis, haemochromatosis
- Thyroiditis (postpartum)
*Congenital: Cretinism - SECONDARY HYPOTHYROIDISM (5% of cases)
- Pituitary and Hypothalamic disease- resulting in reduced TSH and TRH and, hence, reduced stimulation of thyroid hormone production
- E.g. pituitary adenoma, pituitary apoplexy, Sheehan’s syndrome, pituitary surgery, infiltrative disorders, drugs e.g. cocaine
Describe the epidemiology of hypothyroidism?
● 0.1-2% of adults
● 6 x more common in FEMALES
● Most common age of onset > 40 yrs
● Iodine deficiency is seen in mountainous areas (e.g. Himalayas)
What are the presenting symptoms of hypothyroidism?
● INSIDIOUS onset
● Cold intolerance
● Lethargy
● Weight gain
● Reduced appetite
● Constipation
● Dry skin
● Hair loss
● Hoarse voice
● Mental slowness
● Depression
● Cramps
● Ataxia
● Paraesthesia
● Menstrual disturbance (irregular cycles, menorrhagia)
● History of surgery or radioiodine therapy for hyperthyroidism
● Personal/family history of other autoimmune conditions (e.g. Addison’s, T1DM)
● Myxoedema coma (severe hypothyroidism usually seen in the elderly):
*Hypothermia
*Hypoventilation
*Hyponatraemia
*Heart failure
*Confusion
*Coma
What signs of hypothyroidism can be found on physical examination?
- Face
Hertoghe sign (Loss of the lateral third of the eyebrow) classically seen in hypothyroidism although there are a few other conditions where it may also be present (e.g. atopic dermatitis, leprosy) - Hands
o Bradycardia
o Cold hands - Head/Neck/Skin
o Pale puffy face
o Goitre
o Oedema
o Hair loss
o Dry skin
o Vitiligo - Chest
o Pericardial effusion
o Pleural effusion - Abdomen
o Ascites - Neurological
o Slow relaxation of reflexes
o Signs of carpal tunnel syndrome
What investigations are used to diagnose/ monitor hypothyroidism?
- TFTs
- Decreased T4 & T3 levels
- If increased TSH → primary hypothyroidism
- If decreased TSH → secondary hypothyroidism
*Pituitary Insufficiency (may need MRI) - Antibody testing → in autoimmune hypothyroidism
- Anti-TPO → occurs in Hashimoto’s - May cause euvolemic hyponatraemia
How is hypothyroidism managed?
- Levothyroxine → lifelong replacement, adjust dose based on TFTs
- guidelines state to ‘start levothyroxine at a dosage of 25-50 micrograms per day in adults over 65 and adults with a history of cardiovascular disease.’
- TSH should be checked annually following stabilisation of dose
*Raised TSH and Normal T4 suggests poor compliance with levothyroxine
- Dose should be increased by up to 50% in pregnancy (as early as 4-6 weeks of pregnancy)
- Overreplacement with thyroxine increases risk of osteoporosis
- Calcium carbonate reduces absorption of levothyroxine - Myxoedema Coma → severe hypothyroidism causing impaired mental status, hypothermia, hypotension → IV levothyroxine (T4) & liothyronine (T3) + IV hydrocortisone, oxygen + rehydration
What complications may arise from hypothyroidism?
● Myxoedema coma
● Myxoedema madness (psychosis with delusions and hallucinations or dementia)
Summarise the prognosis of hypothyroidism
● Lifelong levothyroxine is required
● Myxoedema coma mortality = 80%
What is meant by subclinical hypothyroidism?
Subclinical Hypothyroidism → raised TSH but normal T3/T4
- <65 yrs + symptoms of hypothyroidism ⇒ trial of levothyroxine
- Older or asymptomatic ⇒ observe and repeat TFTs in 6 months
