Hypothyroidism Flashcards
Thyroid hormones
Thyroid Stimulating Hormone (TSH
Free T4
Free T3
Thyroid stimulating hormone
Released by thyrotroph cells in anterior pituitary in response to thyrotrophin releasing hormone (TRH)
Reflect tissue thyroid hormone action
Plasma Proteins
~99% of T3 and T4 bound to plasma proteins
- TBG
- Albumin
- Pre-albumin
Primary Hypothyroidism- axis
Free T3/T4 low
TSH high
Secondary Hypothyroidism - axis
Free T3/ T4 low TSH low (or 'normal')
hypothyroidism
results from any disorder that results in insufficient secretion of thyroid hormones from thyroid gland
Myxoedema
Severe hypothyroidism and medical. emergency
Primary hypothyroidism aetiology
Goitrous
- Chronic thyroiditis (Hashimoto’s)
- Iodine deficiency
- Drug-induced
- Maternally transmitted
- Hereditary biosynthetic defects
Non-goitrous
- Atrophic thyroiditis
- Post ablative therapy
- post radiotherapy
- Congenital developmental defect
Self Limiting
- Following withdrawal of antithyroid drugs
- Subacute thyroiditis with transient hypothyroidism
- Post-partum thyroiditis
Secondary Hypothyroidism: Aetiology
Diseases of hypothalamus and pituitary. gland
Autoimmune Hypothyroidism
Hashimoto’s THyoriditis
Most common cause of hypothyroidism in western world
Hashimotos Thyroiditis Pathophysiology
Autoimmune destruction of thyroid gland and reduced thyroid hormone production
often family history of autoimmune thyroiditis or other autoimmune disorders
Hashimoto’s thyroiditis Characterisation
Antibodies against thyroid peroxidase
T-cell infiltrate and inflammation microscopically
Hypothyroidism Clinical Features:
Hair and Skin
Coarser, sparse hair Dull, expressionless face Periorbital puffiness Pale cool skin- doughy to touch Vitiligo may be present Hypercarotenaemia
Hypothyroidism Clinical Features: Thermogenesis
Fluid retention
Thermogenesis
- Cold intolerance
Fluid retention
- Pitting Oedema
Hypothyroidism Clinical Features:
Cardiac
Reduced HR
Cardiac dilatation
pericardial effusion
Worsening of heart failure
Hypothyroidism Clinical Features:
Metabolic & GI
Metabolic
- Hyperlipidaemia
Metabolic Rate
- Decreased appetite
- Weight gain
GI
- Constipation
Hypothyroidism Clinical Features: Respiratory
Deep hoarse voice
Macroglossia
Obstructive sleep apnoea
Hypothyroidism clinical features: Neurology/ CNS
Decreased intellectual and motor activities Depression, psychosis Muscle stiffness and cramps Peripheral neuropathy Prolongation of tendon jerks Carpal Tunnel Syndrome Decreased visual acuity
Hypothyroidism Clinical Features: Gynae/ Reproductive
Menorrhagia
Later oligo- or amenorrhoea
Hyperprolactinaemia
Primary Hypothyroidism : Laboratory Investigations
Increased TSH
Decreased free T3/T4
Macrocytosis (Increased MCV) Increased creatine kinase Increased LDL- cholesterol Hyponatraemia - renal tubular water loss hyperprolactinaemia - Increased TRH leads to increased prolactin
Hypothyroidism Management
Main treatment: Levothyroxine (T4)
normal metabolic rate gradually restored
-rapid restoration may cause cardiac arrhythmias
Younger patients
- Levothyroxine at 50-100 ug daily
Elderly (+ history of IHD)
- Levothyroxine25-50 ug daily and adjust every 4 weeks
Dose requirements may increase by 25-50% in pregnancy
Hypothyroidism Management- Follow Up
Check TSH 2 months after any dose change
Once stabilised, TSH checked every 12-18 months
Secondary hypothyroidism
- TSH unreliable
- Titrate dose to drug to fT4 level
Myxoedema Coma: Epidemiology
Typically affects elderly women with long-standing but frequently unrecognised or untreated hypothyroidism
Medical emergency
- Mortality up to 60%
Myxoedema Coma: Findings
ECG
- bradycardia
- Low voltage complexes
- Varying degrees of heart block
- T wave inversion
- Prolongation of QT interval
Type 2 Respiratory Failure
- Hypoxia
- Hypercarbia
- Respiratory Acidosis
Myxoedema Coma Managements
intensive care: ABC
Passively reward
- slow rise in body temp
Cardiac monitoring for arrhythmias
Close monitoring od urinwe output, fluid balance, central venous pressure, blood sugars and oxygenation
Thyroxine cautiously (hydrocortisone)