Too little thyroid hormone and the body’s metabolic accelerator comes off: heart rate
down, temperature down, bowels down, weight up. This page is built as the deliberate
mirror image of NG-284 (Hyperthyroidism) — same sections, same diagrams, opposite findings.
The reversible trap is identical: in primary disease TSH goes the OPPOSITE way to T3/T4,
so hypothyroidism has a HIGH TSH.
🧊 LOW & SLOWSlow heart · cold, dry skin · weight gain · constipation · flat and forgetful.
🧪 TSH ↑ · T3/T4 ↓Primary disease: TSH is the opposite of the hormones.
💊 LEVOTHYROXINELifelong · Early morning, empty stomach · Very-active = too much · Oh baby, it’s pregnancy safe.
🚨 MYXEDEMA COMAFalling consciousness + hypothermia + respiratory failure. ❌ No electric blankets.
🦋
THE GLAND & WHY IT SLOWS DOWN
STEP 1 · CAUSE
Same butterfly gland as NG-284 — this time it cannot keep up with the order it is being given.
🦋 Anatomy first — and yes, hypothyroid can have a goitre too
A goitre is not a direction. In Hashimoto’s the gland is often enlarged
and rubbery early on and shrunken and atrophic later. In iodine deficiency the gland swells trying
to trap what little iodine there is.
🧠 Big gland ≠ busy gland. Always read the labs, never the neck.
⚙️ What T3 and T4 do (identical to NG-284)
They set the basal metabolic rate — how fast every cell burns fuel: temperature, heart rate,
gut motility, growth and brain development, and drug clearance.
Take the hormone away and every one of those slows down. That single sentence generates the whole
symptom list — you do not need to memorize it.
🧠 No hormone = no throttle. Predict the symptom, don’t recall it.
⭐ Cause #1 — Hashimoto’s thyroiditis
Autoimmune. Antibodies (anti-TPO, anti-thyroglobulin) and lymphocytes gradually destroy the
gland. It is the most common cause of hypothyroidism where iodine intake is adequate.
Onset is slow and vague — fatigue and weight gain get blamed on stress or age for years.
Most common in women, and it clusters with other autoimmune disease (type 1 diabetes,
celiac disease, vitiligo, pernicious anemia).
🧠 HashimOtO = LOW & SLOW — the two O’s look like the two “low” arrows.
📋 The other causes — most of them are things WE did
Treated hyperthyroidism — after radioactive iodine or a thyroidectomy. Expected, not a
complication.
Drugs — amiodarone, lithium, some immune-checkpoint cancer drugs.
Iodine deficiency — the leading cause worldwide.
Neck radiation for head and neck cancer or lymphoma.
Central / secondary — a pituitary or hypothalamic problem. Here TSH is low or normal
with a low T4 (see the labs section).
Congenital — screened for at birth, because untreated it causes irreversible intellectual
disability and stunted growth.
🧠 Always ask: “Have you ever had thyroid surgery, radioactive iodine, or neck radiation?”
🔬 Down at the microscope — Hashimoto’s
Instead of tall, hungry cells eating the colloid (hyperthyroid), the picture here
is lymphocytes invading and destroying the follicles. Function falls as tissue is lost, which is why
hypothyroidism from Hashimoto’s is usually permanent.
🧠 Hyper empties the pantry. Hashimoto’s burns down the kitchen.
🤰 The one group you must not miss
Untreated hypothyroidism in pregnancy is linked to miscarriage, pre-eclampsia and impaired
fetal neurological development.
Levothyroxine requirements usually increase during pregnancy, so doses are reviewed and TSH is
monitored more often.
Never stop levothyroxine because a patient becomes pregnant — it is the opposite of what is needed.
🧠 Pregnant + hypothyroid = MORE drug, not less.
🧊
LOW & SLOW — THE SIGNS
STEP 2 · CLUES
Same drawing as NG-284, read down the other column. Every finding is the mirror.
🧍 Head to toe — hyper on the left, hypo on the right
🧠 This is the same diagram as NG-284. If you can rebuild one column from the other,
you own both diseases.
❤️ Cardiac — quiet, but not safe
Bradycardia<60
Diastolic hypertension with a narrow pulse pressure (e.g. 110/90)
Low-voltage ECG; pericardial and pleural effusions in severe disease
High cholesterol and LDL → accelerated atherosclerosis
Reduced exercise tolerance, non-pitting edema
Starting or increasing levothyroxine too fast can unmask angina or precipitate an arrhythmia,
especially in older patients — which is why doses are started low and titrated.
🧠 Narrow pulse pressure = a slow, tight circulation. Hyper does the opposite.
🌡️ Cold — and DRY, not sweaty
Cold intolerance, low body temperature, cool dry coarse skin, brittle nails,
coarse hair with hair loss including the outer third of the eyebrows.
These patients pile on sweaters and blankets in a warm room.
Never use an electric blanket or a rapid active warming device — it vasodilates and
drops an already low blood pressure.
🧠 Hyper = hot & wet. Hypo = cold & dry. Two words each.
🍽️ Weight & gut — eating less, weighing more
Weight gain despite a reduced appetite — plus genuine fluid weight from myxedema
Constipation, hypoactive bowel sounds; paralytic ileus in extreme cases
Bloating and abdominal distension
Diet: low calorie, high fiber, plenty of fluid to manage constipation. No caffeine binges to
chase the fatigue, and no spicy irritants if the gut is already unhappy.
Warn patients that weight will not fall dramatically on replacement therapy — it corrects the
fluid more than the fat.
🧠 Eating like a bird, gaining like a bear.
🧠 Neuro & psych — the change families notice first
Fatigue, sleepiness, slowed thinking, poor memory and concentration
Depression and apathy — often mistaken for primary depression
Slow, deep, hoarse speech; slow-relaxing deep tendon reflexes
Paraesthesia and carpal tunnel syndrome
A falling level of consciousness in a known hypothyroid patient is myxedema coma until proven otherwise.
🧠 Everything about them is slow — including the reflex coming back.
😐 The myxedema face
Myxedema is mucin-rich material deposited in the dermis. It is
non-pitting — press it and no dent stays behind — which distinguishes it from the pitting edema
of heart failure or fluid overload.
🧠 Pit = fluid. No pit = myxedema.
👩 Reproductive & hematology
Heavy or irregular periods (menorrhagia) — the mirror of hyperthyroid amenorrhoea
Infertility and increased miscarriage risk
Reduced libido
Anemia — often normocytic, sometimes macrocytic when pernicious anemia coexists
🧠 Slow metabolism = more bleeding. Hyper = less.
📊 Side by side — the mirror table (identical to NG-284)
Body system
HYPOthyroid 🧊
HYPERthyroid 🔥
Heart rate
Bradycardia, low voltage ECG
Tachycardia, A-fib, palpitations
Blood pressure
Diastolic HTN, narrow pulse pressure
Systolic HTN, wide pulse pressure
Temperature
Cold intolerance, cool DRY skin
Heat intolerance, warm MOIST skin
Weight
GAIN with reduced appetite
LOSS with increased appetite
Bowels
Constipation
Diarrhea
Mood / cognition
Depressed, apathetic, forgetful
Anxious, irritable, insomnia
Reflexes
Slow relaxation phase
Brisk / hyperreflexia
Periods
Heavy / irregular (menorrhagia)
Light or absent (amenorrhoea)
Hair & skin
Coarse hair, hair loss, dry scaly skin
Fine thinning hair, smooth skin
Cholesterol
HIGH
LOW
Eyes
Puffy periorbital edema, lost outer brow
Exophthalmos, lid lag (Graves’)
Emergency
MYXEDEMA COMA
THYROID STORM
🧠 Every row is a see-saw. Learn one side, flip it, you have the other.
The mirror of thyroid storm — and the airway is what kills, not the temperature.
🚨 The whole picture in one diagram
🚨 Recognize it early — consciousness first
EarliestLethargy → stupor → unresponsive
ThenHypoventilation, CO₂ retention, hypoxia
ThenHypothermia · bradycardia · hypotension
ChemistryHyponatremia · hypoglycemia
Respiratory failure is the number-one cause of death — protect the airway before anything else.
Priority equipment at the bedside: an endotracheal intubation set-up and suction.
🧠 Storm burns; coma freezes. Both start in the brain — one agitated, one asleep.
❌ The never-do list
Never use an electric blanket or aggressive active rewarming — peripheral
vasodilation drops an already dangerously low blood pressure. Warm passively with blankets.
Never give sedatives, opioids or hypnotics without an explicit order — they are
cleared extremely slowly and can stop the breathing altogether.
Never let a patient stop levothyroxine because they “feel fine”.
🧠 Warm them slowly, wake them slowly, and guard the airway the whole time.
✅ Nursing priorities
1
AIRWAY & breathing intubation set-up + suction at the bedside; monitor rate, depth, SpO₂ and CO₂
▼
2
Circulation cardiac monitor, frequent vitals, treat hypotension as ordered
▼
3
Warm passively blankets and a warm room — no electric blankets
▼
4
Glucose & sodium check both; expect IV glucose and careful fluid management
▼
5
Find the trigger usually cold exposure, infection, a sedative, or a stopped tablet
Expect IV thyroid hormone replacement plus an IV glucocorticoid (given because
coexisting adrenal insufficiency must be covered before thyroid hormone is pushed).
🧠 Airway · Attitude (LOC) · Ambient warmth · And find the trigger.
⭐ Storm vs coma — one table
THYROID STORM 🔥
MYXEDEMA COMA 🧊
Underlying disease
Hyperthyroidism
Hypothyroidism
Temperature
Very HIGH (fever)
Very LOW (hypothermia)
Heart rate
>140, often A-fib
Bradycardia
Mental state
Agitated, delirious
Lethargic → comatose
The killer
Cardiac collapse / hyperthermia
Respiratory failure
Never give
Aspirin / salicylates
Electric blanket · sedatives
Bedside kit
Cooling blanket, cardiac monitor
Intubation set-up, suction
🧠 Storm = cool them down. Coma = warm them up (slowly) and breathe for them.
💊
LEVOTHYROXINE — TREAT & TEACH
STEP 5 · CARE
One drug, and almost every exam question about it is really a question about timing.
💊 The routine that makes the drug work
🧠 L·E·V·O — Lifelong · Early & empty · Very-active means too much ·
Oh baby, it’s pregnancy safe.
✅ How to take it — the teaching that matters
Same time every morning, on an empty stomach, with a full glass of water
Wait 30–60 minutes before breakfast or coffee
Separate by about 4 hours from calcium, iron, magnesium, antacids, sucralfate, fiber
supplements and soy products — they bind the drug and block absorption
Do not switch brands or between brand and generic without telling the prescriber —
small differences in absorption matter here, and the dose may need rechecking
Missed a dose? Take it when remembered that day. Never double up.
It takes 3–4 weeks to feel better and 6–8 weeks for the labs to settle
🧠 Wake up · Water · Wait.
🚨 Too much drug looks exactly like NG-284
Over-replacement produces hyperthyroid symptoms. Teach patients to report:
Long-term over-treatment raises the risk of atrial fibrillation and osteoporosis.
🧠 If they start looking like the hyperthyroid page, the dose is too high.
❌ Never stop it abruptly
Stopping levothyroxine suddenly can precipitate myxedema coma.
It replaces a hormone; it does not cure the disease. There is no “course” and no finish line.
Practical safety net: keep an emergency supply, refill early, and never run out on a holiday weekend.
🧠 “LevO leaves T4 in the body” — take it away and the body has nothing left.
⚠️ Start low and go slow in the at-risk patient
In older adults and anyone with coronary artery disease, therapy is started at a low dose
and increased gradually, because a sudden rise in metabolic rate increases myocardial oxygen demand and
can provoke angina, an arrhythmia or an MI.
Monitor heart rate, rhythm and any complaint of chest pain at every dose change.
🧠 An old heart cannot take a young metabolism overnight.
💊 Interactions worth knowing
Warfarin — levothyroxine increases its effect; watch the INR and for bleeding
Insulin and oral diabetes drugs — requirements often rise as metabolism speeds up
Amiodarone and lithium can cause the hypothyroidism in the first place
🧠 Speed everything up and every other drug’s math changes.
🥗 Lifestyle & comfort care
Low-calorie, high-fiber diet with adequate fluid for constipation
Extra blankets and warm clothing; keep the room warm
Skin: mild soap, emollients, avoid long hot showers
Plan frequent rest periods and pace activity while the drug takes effect
Reassure them the fatigue and low mood usually lift once the level is right — this is not
“just depression”
🧠 Warmth, fiber, fluid and patience.
🧠 Quiz yourself — no peeking
8 questions with answers
Q1: TSH 14 (high) with a low free T4. Where is the problem?
The thyroid gland — primary hypothyroidism. The arrows point opposite ways, which means
the pituitary is working correctly and shouting at a gland that cannot respond.
Q2: TSH 0.3 (low) with a low free T4. Now where is the problem?
The pituitary or hypothalamus — central/secondary hypothyroidism. Both arrows point the
same way, so the order is not being sent.
Q3: A patient takes levothyroxine with breakfast and a calcium supplement. What do you teach?
Take it on an empty stomach 30–60 minutes before breakfast, and move the calcium to a
different time of day — about 4 hours apart. Food and calcium block absorption.
Q4: Which new symptom on levothyroxine do you report first — mild constipation, chest
pain, dry skin, or feeling cold?
Chest pain. It suggests the dose is too high for that heart, and it is the one answer
that is an emergency.
Q5: A hypothyroid patient is found lethargic, cold, with an RR of 8.
First action?
Airway and breathing — this is myxedema coma and respiratory failure is what kills.
Get help, support ventilation, and make sure the intubation set-up and suction are at the bedside.
Q6: Why is an electric blanket the wrong choice for the same patient?
Rapid surface warming causes peripheral vasodilation, which drops an already low blood
pressure and can cause cardiovascular collapse. Warm passively with ordinary blankets.
Q7: Your patient stopped their levothyroxine two months ago because they “felt fine”.
What do you teach?
It is lifelong replacement, not a cure or a course. Feeling well means the dose is right,
not that the disease is gone. Stopping can lead to myxedema coma.
Q8: A patient on levothyroxine becomes pregnant. What usually happens to the dose?
It usually needs to increase, and TSH is monitored more frequently. Levothyroxine is safe
in pregnancy and must not be stopped.