Hyperthyroidism

This man has exopthalmos: a bulging outwards of the eyes, caused by hyperthyroid. He also just saw Margaret Thatcher getting dressed.

Definition

Overactive production of the thyroid hormone.

Epidemiology

Does exactly what it says in the red box on the left.

Pathophysiology

Thyroid gland produces to much thyroid. This can be due to a number of things. Thyroxine (T₃) is reponsibile for maintaining the basal metabolic rate. Metabolism is all the chemical reactions that happen in the body. Basically, your body speeds up all its processes as thyroxine levels increase. Hence, you lose weight, get a tachycardia, get diarrhoea etc.

Just imagine your body's gone a bit crazy when it's doing stuff.

Graves disease

The commonest type, usually associated with a big goitre. It happens when an IgG antibody is produced, which mimics the action of TSH, thus causing growth in gland tissue and overproduction. Look out for exophthalmos (bulgy eyes).

Toxic nodular goitre

Rare, where one of more of the lumps in a goitre becomes hypersecretory. It's unlikely you will see one of these, but doesn't hurt to be in the know!

Clinical Features

Medical Emergency - Thyroid storm is not a nice thing to get, and needs treating promptly! Presents with fever, tachycardia, delirium or coma, seizures, vomiting, diarrhoea and jaundice.

Assuming you don't get any emergency problems with your thyroid, these are some of the less emergency symptoms:

• Neck - goitre
• GI - diarrhoea/steatorrhoea, weight loss, change in appetite
• Neuromuscular - fine tremor, brisk reflexes, proximal myopathy, exopthalmos (bulgy eyes), lid lag (sclera visible betwen top of pupil and bottom of upper eyelid), weakness & fatigue, proximal myopathy
• Skin - urticaria, pruritis, sweating, sweaty palms, palmar erythema, hair thinning,
• Psychological - anxiety, psychosis, irritability, loss of libido
• Other - gynaecomastia, oligomenorrheoa/amennorhoea, tachycardia (AF)

Investigations

• TFTs - well obviously. This includes TSH, T₃ and T₄. If TSH is high, that means there is something wrong in the hypothalamus. Otherwise it's a problem in the thyroid gland.
• Autoantibodies -specifically ones for Graves' disease:
  • antimicrosomial
  • antithyoglobulin
  • TSH-receptor antibodies
• Imaging - thyroid USS

Management

Drug

Carbimazole (10mg 2-3/day) is the treatment of choice (propylthiouracil is an alternative). These are antithyroid drugs. Either they can do

• Block and replace - knock out the thyroid totally and give thyroxine
• Dose titration - give titrated amounts of antithyroid

The aim is to avoid induced hypothyroidism. TFTs are repeated monthly and patients with a sore throat or rash need an FBC as it may be a sign of bone marrow suppression leading to agranulocytosis. Radioiodine is used as first-line in teenagers (avoid in pregnancy)

Surgery

Removal of the thyroid gland (thyroidectomy) is the next option if suboptimal results are acheieved with pharmacological therapy. Complications: haemorrhage, hypoparathyroidism, vocal cord paralysis. Follow-up required for hypothyroidism.

Prognosis

Dogs can smell thyroxine. It is likely the person will develop cynophobia should they have chronic hyperthyroidism.