Thyroid action
- 90% bound to thyroxine binding globulin (TBG) in circulation. Only active T3 is utilized by cells. Many drugs and factors affect levels of TBG.
- Sick euthyroid syndrome – systemically ill patients have low T4/T3 due to downregulation of thyroid receptors. Thyroid tests should be performed after illness subsided.
- Pregnancy – TBG and T4 increased.
- Amiodarone – lowers T4 conversion
Graves
Graves disease is the most common cause of hyperthyroidism followed by toxic multinodular goitre. However, there are many other causes .
Etiology
- IgG antibodies against TSH-R, HLA DR3/B8 association
- May accompany pernicious anaemia, vitiligo, myasthenia gravis
Clinical features
- Hyperthyroidism presents with many signs and symptoms
- Lid lag – only in graves
- Detmopathy and acropachy is rare
- Atrial fibrillation – elderly
- Excessive height and weight gain – children (weight loss in adults)
Diagnosis
- Clinically
- TSH supressed, raised T4/T3
Treatment
- Carbimazole [20-40mcg/day], PTU [100-200mcg/t.i.d]
- Propranolol [40-80mg/t.i.d] – inhibit T4 conversion and provides symptomatic relief
- Stop B blockers when clinically euthyroid
- Drugs have risk of agranulocytosis
- Thyroid radiotherapy/ surgery also possible
- Give potassium iodide t.i.d to decrease gland vascularity before surgery
Thyroid storm
- Life threatening condition , untreated graves disease
- Severe hyperpyrexia, tachycardia, cardiac failure, liver failure
- Precipitated by infection or stress
- Urgent propranolol, corticosteroids, anti-thyroid drugs, potassium iodide