Understanding
Thyroid Disease

What the hormones do

• Control metabolic rate — how fast the body uses energy
• Regulate heart rate, temperature and digestion
• Essential for brain development in babies and children
• Influence mood, weight, fertility and cholesterol

Thyroid problems are common

• Women are affected about 5–8 times more often than men
• Risk rises with age and with a family history
• Autoimmune disease is the most common cause in Australia
• Most conditions respond very well to treatment

Three main ways it misbehaves

• Underactive — too little hormone (hypothyroidism)
• Overactive — too much hormone (hyperthyroidism)
• Enlarged or lumpy — goitre and nodules, which may or may not affect hormone levels

Why TSH is the key blood test

Because of this loop, TSH acts like a mirror of thyroid function: a high TSH usually means the thyroid is underactive (the pituitary is shouting at a sluggish gland), while a low TSH means there is too much thyroid hormone (the pituitary goes quiet). One small blood sample picks up problems early — often before symptoms appear.

Who's in charge of production?

Thyroid cells take up iodine (from seafood, dairy, iodised salt and bread fortification in Australia) and build T4 and T3. Nearly all body T3 is made by converting T4 in other tissues. Pregnancy, illness and some medicines shift these requirements — which is why thyroid blood tests are checked more often at those times.

Common causes

• Hashimoto's thyroiditis — the immune system attacks the thyroid (most common cause in Australia)
• Thyroid surgery or radioactive iodine for previous overactivity — leaving too little working tissue
• Medicines — lithium, amiodarone; too little or too much iodine
• Rarely — pituitary problems (the "secondary" form)

What the blood tests show

• TSH high — the pituitary is pushing a sluggish gland
• Free T4 low — confirms the gland is falling behind
• Thyroid antibodies (TPO) — point to Hashimoto's as the cause
• Cholesterol often rises; anaemia can appear on routine tests

Common causes

• Graves' disease — antibodies switch the gland permanently "on" (most common, especially under 50)
• Toxic nodular goitre — one or more nodules produce hormone on their own (more common over 60)
• Thyroiditis — a temporary leak of stored hormone after pregnancy or a viral illness; often settles by itself
• Medicines — excess thyroid hormone replacement or amiodarone

What the blood tests show

• TSH low or undetectable — the pituitary switches off
• Free T4 and/or T3 high — confirms the excess
• TRAb (Graves' antibody) and scan patterns separate the causes
• Untreated, it strains the heart and can thin the bones — treatment matters

What actually happens

• The immune system makes TRAb antibodies that mimic TSH
• They permanently order the gland to produce hormone — bypassing the brain's control loop
• TSH falls to zero; the gland itself often enlarges into a smooth goitre
• Can occur at any age, but typically women 20–50

Thyroid eye disease (TED)

• The same antibodies inflame tissues behind the eyes
• Eyes look bulgy or staring; grittiness, double vision, pressure
• Smoking greatly increases the risk and severity — quitting is treatment
• Active phase lasts 12–24 months, then stabilises; severe cases referred to specialists

Course & outlook

• Roughly half achieve lasting remission after a 12–18 month course of antithyroid tablets
• Others move on to radioactive iodine or surgery
• Pregnancy, fertility and eye disease all influence the choice — discuss plans early
• Lifelong monitoring is standard, as late relapse or underactivity can occur

Iodine deficiency

Worldwide the top cause. When iodine is scarce, TSH rises and the gland swells to compensate. Rare in Australia since bread salt fortification began in 2009, but still seen in strict exclusion diets.

Autoimmune disease

Hashimoto's can swell the gland (often with a pebbly texture) before it shrinks; Graves' produces a smooth, firm enlargement with overproduction.

Nodular change

With age, local patches of thyroid tissue grow independently, forming lumps. Multinodular goitres are very common in people over 60 and usually grow slowly over years.

Pregnancy, hormones & other

Pregnancy hormones can enlarge the gland slightly. Less commonly, thyroiditis, cysts, benign tumours — or rarely cancer — present as swelling.

What it can feel like

• Tightness or fullness at the base of the neck; difficulty swallowing big pills or food
• A visible lump that moves up and down when you swallow
• Large goitres can press on the windpipe — a noisy breath, cough or breathlessness lying flat
• Many goitres cause no symptoms at all and are found incidentally

When enlargement is checked urgently

• A lump that is hard, fixed or growing quickly
• Hoarse voice, new swallowing trouble or noisy breathing
• Enlarged, firm lymph nodes in the neck
• These features don't mean cancer — but they always deserve prompt assessment

Getting the most from your tablet

• Take on an empty stomach — 30–60 min before breakfast (or 4 h after dinner) with water
• Separate from calcium, iron, antacids and soy by at least 4 hours — they block absorption
• Don't swap brands without checking — small variations can shift levels

Monitoring

• TSH rechecked 6–8 weeks after any dose change
• Once stable, bloods every 6–12 months
• Recheck after brand changes, significant weight change, or new medications

Too little vs too much

• Under-dosed: the hypo symptoms creep back
• Over-dosed: palpitations, tremor, sweating — and long-term bone thinning and heart strain
• Never self-adjust; report symptoms instead

Papillary (~80%)

Slow-growing, often in younger people and women. Spreads first to neck lymph nodes, which barely changes the outlook. 20-year survival above 95%.

Follicular (~10%)

Also slow-growing; can spread via the bloodstream to lung or bone in a minority. FNA can't fully separate it from benign follicular lumps — surgery sometimes confirms the diagnosis.

Medullary (~2–4%)

Arises from different cells that make calcitonin. Rare and sometimes inherited (RET gene) — family screening is arranged when it's found.

Anaplastic (<2%)

The rare aggressive form of older age, with rapid neck growth. This is the exception the whole TI-RADS system exists to catch early — or prevent.

How it's treated

• Surgery — half or all of the gland removed; often curative by itself for small papillary cancers
• Radioactive iodine after surgery for some types, to ablate leftover tissue
• Lifelong levothyroxine, dosed to keep TSH suppressed so any remaining cells stay dormant
• Follow-up — neck ultrasound and thyroglobulin blood test (a tumour marker) at set intervals

What raises the risk

• Radiation exposure to the neck in childhood (e.g. previous cancer treatment)
• Family history of thyroid cancer or inherited syndromes (FAP, MEN2)
• Female sex — women are affected about three times more often
• Most people with risk factors never develop it; screening is targeted, not automatic

Pregnancy & postpartum

• The baby depends entirely on mum's thyroid hormone until ~12 weeks — untreated hypothyroidism affects baby's brain development
• Levothyroxine is safe in pregnancy; the dose usually needs a 30% increase — test at 4–6 weeks of pregnancy if planned
• Postpartum thyroiditis affects 1 in 20 new mothers: a hyper phase, often followed by a hypo phase, within the first year
• Graves' in pregnancy uses PTU first, then carbimazole; TRAb levels are monitored near term

"Borderline" results (subclinical)

• Subclinical hypothyroidism — high TSH with normal T4. Common; treatment offered for TSH >10, symptoms, antibodies, or pregnancy planning
• Subclinical hyperthyroidism — low TSH with normal T4. Watched carefully, treated when it strains the heart or bones
• Both are retested in 6–12 weeks before acting — the axis often settles itself
• Non-thyroid illness and some drugs can mimic these patterns

Older adults

Hyperthyroidism often hides behind fatigue, weight loss and an irregular heart rhythm (atrial fibrillation) rather than the classic "wired" picture. Overtreatment risk is higher, so levothyroxine doses start lower.

Hashimoto's over time

The gland usually shrinks back after years of inflammation. Some people swing briefly hyper before settling hypo. Goitre, coeliac disease, type 1 diabetes and vitiligo cluster with it — worth screening for.

Thyroiditis patterns

Painless (postpartum or autoimmune), subacute (painful, after a virus, tender neck), drug-induced (amiodarone, lithium, immunotherapy). Most resolve; a proportion end up permanently underactive.

Worth discussing a thyroid test if you have

• Persistent unexplained tiredness, weight change, or temperature intolerance
• New racing heart, tremor, anxiety, or irregular pulse
• A lump or swelling in the neck, or a hoarse voice that won't settle
• Family history; autoimmune conditions (type 1 diabetes, coeliac); medicines such as lithium, amiodarone or immunotherapy; pregnancy planning

Seek care promptly (not routine) for

• Fast pulse with chest pain, fainting or severe breathlessness
• Fever, confusion and extreme restlessness together (thyroid storm)
• Rapidly enlarging neck lump, noisy breathing or trouble swallowing
• Severe drowsiness with cold, puffy skin (myxoedema — late severe hypo)