Thyroid

HYPERTHYROIDISM

Diagnostic findings

• v TSH

Pathogenesis

• Hypermetabolic - warm skin, ^sweating, loose nails, thin nails, diarrhoea, v exercise tolerance, osteoporosis, agitation, low cholesterol
• ^ sympathetic activity - staring, lid lag,
• Pressure effects of goitre - airway obstruction, difficulty swallowing
• Sexual function - infertility, menstrual changes
• Other - urinary frequency, nocturia
  + Grave's disease - bulging or gritty eyes > optic nerve traction > visual change

Cause - Pathology - Nuclear Scan

Grave's disease (COMMONEST)

• Autoimmune - TSH receptor antibodies > stimulate thyroid + antibodies to ocular muscle
• Nuclear scan - ^ diffuse uptake

Hashimoto's thyroiditis

• Autoimmune - TSH receptor antibiodies (stimulation) followed by immune destruction / chronic inflammation (failure)
• Nuclear scan - ^ uptake (initial), v uptake (later)

Toxic adenoma

• ^ Focal hyperplasia with autonomous function
• Nuclear scan - ^ focal uptake

Toxic multinodular goiter

• Diffise hyperplasia with autonomous function
• Nuclear scan - ^ diffuse patchy uptake

Iodine-induced

• Acute or chronic iodine load
• Nuclear scan - high uptake

Thyroiditis (various types)

• Inflammation with release of pre-formed hormone but no new synthesis
• Nuclear scan - no uptake

Thyroxine OD

• Exogenous thyroid hormone
• Nuclear scan - no uptake (-ve feedback suppression)

Complications

• High output heart failure
• Atrial fibrillation
• Glucose intolerance

Treatment principles

• v sympathetic stimulation - beta blockers
• block organification - thionamides e.g. PTU - propylthiouracil, carbimazole OR iodine (Wolf-Chaikoff effect)
• block peripheral conversion T4>T3 - iodine, steroids

Definitive treatment - pros / cons

Radioactive iodine

• Pros - effective and long lasting (esp Grave's), one treatment
• Cons - may make opthalmopathy worse, may temporarily worsen hyperthyroidism, teratogenic/mutagenic, infertility

Thioamides

• Pros - cheap, reversible
• Cons - long term administration, side effects, teratogenic (at higher doses)

Surgery

• Pros - rapid response
• Cons - General (bleeding, infection), Damage to other structures (Parathyroids/low Ca++, laryngeal nerve/hoarseness, airway obstruction)
• Post surgery, radiation treatment patients may need to go thyroxine
  Some patients on thioamides are placed on a 'block-replace' regime with thyroxine for better control

HYPOTHYROIDISM

Diagnosis

• ^ TSH, v FT4 (clinical)
• ^ TSH, <> FT4 (subclinical)
• Non-high TSH, v FT4 (secondary hypothyroidism)
  
  v TSH, v FT4 normal in acute or critical illness

Pathogenesis / Clinical features (often vague initially)

(many be altered by concurrent endocrine changes in hypopituitarism)

• Hypometabolic - fatigue, slow movement/speech, cold intolerance, weight gain, constipation, v HR, cool/dry skin, anaemia/pallor, v mentation/coma
• Altered sex function - irregular periods, infertility, v libido
• Myxoedema (glycoaminoglycan deposition) - coarse hair/skin, brittle nales, puffy face/eyes, large tongue, hoarse voice, median n compression/carpal tunnel

Causes

• Surgical removal
• Previous radiation Rx
• Inadequate iodine
• Hashimoto's thyroiditis (mid-late) - also causes encephalopathy

Complications

• Heart failure
• Hypoventilation
• Sleep apnoea
• Gastric atrophy / Pernicious anaemia
• SIADH - low serum soidum
• Hypertension
• Hyperlipidaemia

Treatment

• Thyroxine