Thyroid Disease & Common Electrolyte Disturbances

Thyroid Disease & Electrolyte Disturbances

Thyroid Function Tests

• TSH: most sensitive test; Ôåô TSH = hyperthyroidism; Ôåæ TSH = hypothyroidism
• Free T4 and T3: confirm diagnosis; Ôåæ in hyperthyroidism, Ôåô in hypothyroidism

Hypothyroidism

• Causes: Hashimoto's thyroiditis (anti-TPO Ab), post-radioiodine/thyroidectomy, iodine deficiency
• Features: weight gain, cold intolerance, constipation, bradycardia, dry skin, hair loss, fatigue, delayed relaxation reflexes, myxoedema
• Treatment: levothyroxine (T4); titrate to TSH 0.5–2.5 mU/L

Hyperthyroidism

• Causes: Graves' disease (TSH receptor Ab = TRAb), toxic multinodular goitre, toxic adenoma, thyroiditis
• Features: weight loss, heat intolerance, diarrhoea, palpitations, AF, tremor, lid lag, exophthalmos (Graves'-specific), pretibial myxoedema
• Treatment: carbimazole (blocks thyroid peroxidase), propranolol (symptom control), radioiodine, thyroidectomy

Thyroid Storm

• Precipitants: surgery, infection, iodine load, RAI in unprepared patient
• Features: high fever, tachycardia, AF, confusion/agitation, vomiting
• Treatment: propranolol, carbimazole/PTU, Lugol's iodine (>1 h after antithyroid drug), hydrocortisone, dantrolene if hyperthermia

Hyponatraemia

• Definition: Na+ <135 mmol/L; severe: <125 mmol/L
• SIADH: euvolaemic hypona, urine osmolality >100, urine Na+ >40; causes: lung cancer (SCLC), CNS disease, drugs (SSRIs, carbamazepine)
• Hypervolaemic: HF, cirrhosis, nephrotic (Ôåô effective circulating volume → RAAS)
• Hypovolaemic: GI losses, Addison's disease, diuretics
• Correction: fluid restrict (SIADH); hypertonic saline only if severe symptoms; avoid correction >8–10 mmol/L/24 h (osmotic demyelination syndrome)

Hyperkalaemia

• ECG: peaked T waves → prolonged PR → wide QRS → sine wave → VF
• Treatment: calcium gluconate (10 mL 10%) — membrane stabilisation; insulin + dextrose (shift K+ into cells); salbutamol nebuliser; calcium resonium/patiromer (remove K+); dialysis if refractory