Pituitary, Thyroid & Parathyroid Disorders - Cheat Sheet
Your last-minute revision companion for endocrine crisis management, hormone axis dysfunction, and exam-critical nursing interventions. Master the paired opposites (too much vs. too little), the two life-threatening crises, and the must-know labs and treatments.
Posterior Pituitary: ADH Disorders
Common values
Value
135–145 mEq/L
Symbol
Na+
Quantity
Normal serum sodium
Value
280–295 mOsm/kg
Symbol
Posm
Quantity
Normal serum osmolality
Value
1.005–1.030
Symbol
USG
Quantity
Normal urine specific gravity
Value
<120 mEq/L
Symbol
Na+
Quantity
SIADH hyponatremia threshold (symptomatic)
Important facts
- ADH RETENTION: SIADH = Soaked (retains water, low sodium, restrict fluids)
- ADH LOSS: DI = Dry (loses water, high sodium, replace fluids + DDAVP)
- SIADH labs: LOW serum sodium, LOW osmolality; HIGH urine sodium & osmolality
- DI labs: HIGH serum sodium & osmolality; LOW urine osmolality & specific gravity
- SIADH cornerstone: FLUID RESTRICTION (even when thirsty); hypertonic saline (3%) only for severe/symptomatic hyponatremia
- CORRECT sodium SLOWLY in SIADH (≤8–10 mEq/L per 24 hrs) to avoid osmotic demyelination syndrome
- DI management: replace fluids + central DI → desmopressin (DDAVP) synthetic ADH; nephrogenic → high fluid intake + NSAIDs/thiazides
- SIADH triggers: malignancy (especially SCLC), CNS disorders (meningitis, head trauma, seizures), pulmonary disease, surgery, drugs (carbamazepine, SSRIs, vincristine)
- DI post-op risk: highest after pituitary surgery; monitor output/specific gravity closely
- Seizure precautions for SIADH (severe hyponatremia <120 mEq/L causes cerebral edema)
Key definitions
Antidiuretic Hormone (ADH/Vasopressin)
Example
Normal ADH levels → kidneys concentrate urine (high specific gravity) and retain water
Posterior pituitary hormone that promotes kidney water reabsorption to conserve body water and maintain osmolality.
SIADH (Syndrome of Inappropriate ADH)
Example
Small-cell lung cancer patient with low sodium (125 mEq/L) and concentrated urine despite hypo-osmolal state
Excessive ADH secretion causing water retention, dilutional hyponatremia, and concentrated urine despite low serum osmolality.
Diabetes Insipidus (DI)
Example
Post-hypophysectomy patient losing 15 L/day of dilute urine with urine specific gravity of 1.002
Deficiency of ADH (central) or renal unresponsiveness (nephrogenic) causing massive dilute polyuria and hypernatremia risk.
Diagrams to know
- ADH feedback loop: osmolality/volume change → posterior pituitary → ADH release → kidney aquaporin channels → water reabsorption
- SIADH vs DI comparison chart (H2O retention vs loss, sodium direction, urine vs serum osmolality)
Thyroid Disorders: Hyperthyroidism & Thyroid Storm
Common values
Value
0.8–1.8 ng/dL
Symbol
FT4
Quantity
Normal Free T4
Value
2.3–4.2 pg/mL
Symbol
FT3
Quantity
Normal Free T3
Value
0.5–5.0 mIU/L (varies by lab)
Symbol
TSH
Quantity
Normal TSH
Value
>39.5–40°C (often 40–41°C hyperpyrexia)
Symbol
T°
Quantity
Thyroid storm temperature threshold
Important facts
- Hyperthyroidism labs: ↑T3, ↑T4, ↓TSH (in primary disease); radioiodine uptake elevated
- Hyperthyroid signs: weight LOSS despite ↑appetite, heat intolerance, diaphoresis, tachycardia/palpitations/AFib, hypertension, tremor, insomnia, diarrhea, warm moist skin, nervousness
- Graves'-specific: exophthalmos (bulging eyes—autoimmune) + goiter; occurs in both eyes (infiltrative ophthalmopathy)
- Antithyroid drugs (methimazole & PTU): block hormone synthesis; effects take 4–8 weeks; must TEACH TO REPORT sore throat/fever (agranulocytosis = bone-marrow suppression)
- PTU preferred in FIRST TRIMESTER pregnancy (crosses placenta less than methimazole; methimazole teratogenic—aplasia cutis)
- Beta-blockers (propranolol): DO NOT treat the underlying disease, only symptom relief (tachycardia, tremor, anxiety); effect is rapid
- Iodine (Lugol's solution, SSKI): GIVE AFTER antithyroid drugs (NOT before); reduces gland vascularity/hormone release within 24–48 hrs; DILUTE in juice, give through STRAW (stains teeth); brief effect only
- Radioactive iodine (I-131): ablates thyroid → permanent hypothyroidism in most patients (need lifelong levothyroxine); avoid pregnancy for 6 months post-treatment
- Thyroidectomy: most definitive cure; keep tracheostomy set, O2, suction at bedside (airway emergency); support neck; check behind neck for hemorrhage (not just front of dressing)
- Post-thyroidectomy complications: hemorrhage (most common early), laryngeal nerve damage (hoarseness = recurrent laryngeal nerve injury), hypocalcemia/tetany (parathyroid damage)
Key definitions
Thyroid Hormone (T3 & T4)
Example
Excess T4/T3 = tachycardia, weight loss, heat intolerance (metabolism speeds up)
Metabolic hormones produced by thyroid follicles; set basal metabolic rate; require iodine.
TSH (Thyroid-Stimulating Hormone)
Example
Graves' disease: LOW TSH + HIGH free T4 (feedback loop shows gland is overactive)
Anterior pituitary hormone driving thyroid secretion; inverse feedback (low TSH = high T3/T4 in primary hyperthyroidism).
Graves' Disease
Example
Exophthalmos + goiter + tachycardia + heat intolerance = classic Graves' presentation
Autoimmune hyperthyroidism; TSH-receptor antibodies stimulate thyroid; most common cause of hyperthyroidism.
Thyroid Storm (Thyrotoxic Crisis)
Example
Poorly controlled hyperthyroid patient post-op: fever 41°C, HR 160, delirium → requires emergency intervention
Life-threatening exacerbation of hyperthyroidism with uncontrolled hormone release; triggered by infection, surgery, stress, or iodine exposure.
Diagrams to know
- HPG axis: hypothalamus (TRH) → anterior pituitary (TSH) → thyroid (T3/T4); negative feedback (high T3/T4 suppresses TRH & TSH)
- Post-thyroidectomy assessment sequence: airway patency → hemorrhage → voice/nerve function → hypocalcemia signs (Chvostek/Trousseau)
Reactions or equations
Thyroid hormone effects: ↑T3/T4 → ↑metabolic rate, ↑heat production, ↑O2 consumption, ↑cardiovascular workload
Note
This is why thyroid storm is a medical emergency—uncontrolled metabolic overdrive
Conditions
Acute hyperthyroidism or thyroid storm
Thyroid Disorders: Hypothyroidism & Myxedema Coma
Common values
Value
25–50 mcg once daily (elderly/cardiac: start ~25 mcg)
Symbol
Synthroid
Quantity
Levothyroxine initial dose (adult)
Value
75–150 mcg once daily
Symbol
Synthroid
Quantity
Levothyroxine typical maintenance
Value
<32°C (profound hypothermia)
Symbol
T°
Quantity
Myxedema coma core temperature threshold
Important facts
- Hypothyroidism labs: ↓T3, ↓T4, ↑TSH (in primary disease); indicates gland failure with compensatory ↑TSH from pituitary
- Hypothyroid signs: weight GAIN, cold intolerance, fatigue/lethargy, bradycardia, constipation, dry coarse skin/hair, hair loss, depression, slowed cognition, myxedema (non-pitting facial/periorbital edema)
- Levothyroxine (synthetic T4): ORAL on EMPTY stomach, 30–60 min BEFORE breakfast, same time daily; DO NOT take with calcium, iron, antacids (block absorption)
- Levothyroxine dosing: START LOW & GO SLOW in elderly/cardiac patients (excess T4 increases myocardial O2 demand → angina/arrhythmia); usual adult ~100 mcg/day initially
- Levothyroxine effect: gradual (takes weeks to reach steady state); NEVER stop abruptly (risk of relapse/coma)
- Over-replacement signs: hyperthyroid symptoms (tachycardia, tremor, heat intolerance, palpitations, weight loss) → reduce dose
- Under-replacement signs: persistent fatigue, cold intolerance, weight gain, bradycardia → increase dose
- Myxedema coma triggers: cold exposure, infection, sedatives, abrupt levothyroxine discontinuation, severe untreated hypothyroidism
- Myxedema coma management: IV levothyroxine (loading dose ~200–500 mcg IV, then lower maintenance doses), airway/ventilation support, WARM GRADUALLY (passive warming—active causes vasodilation/shock), IV glucose (hypoglycemia risk), IV fluids, corticosteroids (because of adrenal insufficiency often present)
Key definitions
Hypothyroidism
Example
Patient on levothyroxine post-radioactive iodine therapy; requires lifelong replacement
Insufficient thyroid hormone; slows metabolism; most commonly from Hashimoto's thyroiditis (autoimmune) or post-ablation.
Myxedema
Example
Puffy, doughy facial appearance + coarse dry skin in severe chronic hypothyroidism
Non-pitting edema in hypothyroidism caused by glycosaminoglycan/fluid accumulation in subcutaneous tissue (face, periorbital).
Myxedema Coma (Myxedema Crisis)
Example
Elderly patient found unresponsive in cold environment; temperature 32°C, BP 80/50, respiratory depression → requires emergency IV levothyroxine
Life-threatening decompensated hypothyroidism with hypothermia, hypotension, hypoglycemia, hypoventilation, and decreased consciousness.
Diagrams to know
- Levothyroxine absorption pathway: empty stomach → rapid GI absorption → peripheral conversion T4 → T3 (active form)
- Myxedema coma cascade: untreated hypothyroidism → decompensation → hypothermia + hypotension + respiratory depression → coma
Reactions or equations
Hypothyroid metabolic effects: ↓T3/T4 → ↓metabolic rate, ↓heat production, ↓O2 consumption, ↓cardiovascular workload → bradycardia, hypotension
Note
Severe hypothermia + profound bradycardia + hypotension can mimic death; continue resuscitation in myxedema coma
Conditions
Chronic hypothyroidism or myxedema coma
Parathyroid Disorders: PTH, Calcium & Phosphate
Common values
Value
8.5–10.5 mg/dL
Symbol
Ca
Quantity
Normal total serum calcium
Value
4.5–5.5 mg/dL (physiologically active)
Symbol
Ca2+
Quantity
Normal ionized calcium
Value
2.5–4.5 mg/dL
Symbol
PO4
Quantity
Normal serum phosphate
Value
10–65 pg/mL (lab-dependent)
Symbol
PTH
Quantity
Normal PTH
Value
<7 mg/dL
Symbol
Ca
Quantity
Severe hypocalcemia (symptomatic)
Important facts
- Normal serum calcium: 8.5–10.5 mg/dL (ionized Ca 4.5–5.5 mg/dL is physiologically active)
- Calcium & phosphate MOVE OPPOSITE: ↑PTH → ↑Ca, ↓phosphate; ↓PTH → ↓Ca, ↑phosphate
- Normal phosphate: 2.5–4.5 mg/dL
- Hyperparathyroidism presentation (BONES, STONES, GROANS, MOANS): bone pain/osteoporosis/fractures, kidney stones (hypercalciuria), GI upset (constipation/ulcers/pancreatitis), psychiatric symptoms (mood changes, anxiety, depression)
- Hyperparathyroidism management: hydration (IV normal saline) + loop diuretics (furosemide) to promote urinary calcium loss (NOT thiazides—they retain calcium); bisphosphonates/calcitonin; parathyroidectomy (definitive); monitor for hypocalcemia post-op
- Hypoparathyroidism labs: LOW PTH, LOW calcium, HIGH phosphate
- Hypoparathyroidism acute: TETANY—neuromuscular hyperexcitability from hypocalcemia; POSITIVE CHVOSTEK'S (facial twitch on cheek tap), POSITIVE TROUSSEAU'S (carpal spasm with BP cuff), numbness/tingling (perioral, fingers), muscle cramps, laryngospasm (airway emergency), seizures
- Hypoparathyroidism management: acute tetany → IV calcium gluconate stat (have ready after any neck surgery); chronic → oral calcium + active vitamin D (calcitriol); high-calcium low-phosphate diet; seizure/airway precautions
- Post-thyroidectomy/parathyroidectomy: assess voice (laryngeal nerve), check for tremor/numbness (hypocalcemia), monitor serum calcium levels
- Hypercalcemic crisis: polyuria/dehydration, cardiac arrhythmias (shortened QT), altered mental status, renal failure
Key definitions
Parathyroid Hormone (PTH)
Example
↑PTH → pulls calcium from bone + increases GI/renal calcium retention → serum Ca rises
Hormone from parathyroid glands that RAISES serum calcium by increasing bone resorption, GI absorption, and renal reabsorption; LOWERS phosphate.
Hyperparathyroidism
Example
Post-menopausal woman: high PTH + high calcium + kidney stones + bone pain
Excess PTH causing hypercalcemia and hypophosphatemia; primary (parathyroid adenoma/hyperplasia), secondary (renal disease), or tertiary.
Hypoparathyroidism
Example
Post-thyroidectomy patient: low calcium + high phosphate + positive Chvostek/Trousseau signs + tetany
Deficient PTH (often post-neck surgery) causing hypocalcemia and hyperphosphatemia; manifests as neuromuscular hyperexcitability/tetany.
Diagrams to know
- PTH effect on calcium & phosphate: ↑PTH → bone resorption + GI Ca absorption + renal Ca reabsorption + phosphate excretion
- Chvostek's sign technique: tap facial nerve anterior to ear → facial muscles twitch (positive = hypocalcemia)
- Trousseau's sign technique: inflate BP cuff above systolic for 3 min → wrist/hand carpal spasm (positive = hypocalcemia)
Reactions or equations
PTH axis: ↓serum Ca → parathyroid chief cells → ↑PTH release → kidney/bone/gut absorption ↑Ca, ↓phosphate → serum Ca normalized (negative feedback)
Note
This feedback is sensitive and fast; disruption causes acute symptoms
Conditions
Normal calcium homeostasis
Nursing Pharmacology: Key Drugs
Common values
Value
5–20 mg TID (or divided doses up to 60 mg/day)
Symbol
Tapazole
Quantity
Methimazole dose (adult)
Value
100–150 mg TID
Symbol
Propyl-thyracil
Quantity
PTU dose (adult)
Value
10–40 mg QID
Symbol
Inderal
Quantity
Propranolol dose (hyperthyroidism)
Value
5–10 mcg BID (individualized)
Symbol
Stimate/DDAVP
Quantity
DDAVP intranasal typical dose
Important facts
- Antithyroid drugs (methimazole/PTU): TEACH PATIENT TO REPORT sore throat, fever, unusual bruising/bleeding (agranulocytosis = life-threatening bone-marrow suppression)
- PTU vs Methimazole: PTU preferred in FIRST TRIMESTER (methimazole teratogenic); methimazole after first trimester (easier dosing, fewer doses)
- Iodine (Lugol's, SSKI): GIVE AFTER starting antithyroid drugs (not before—iodine alone can worsen hyperthyroidism); DILUTE, GIVE THROUGH STRAW (stains teeth); effect within 24–48 hrs (brief—days to weeks)
- Radioactive iodine (I-131): causes hypothyroidism in 60–80% of patients within first year → lifelong levothyroxine needed
- DDAVP watch: AVOID over-replacement (can cause water intoxication/SIADH/hyponatremia); teach patient signs (headache, drowsiness, nausea, weight gain)
- Levothyroxine must-knows: TAKE ON EMPTY STOMACH (food impairs absorption); NEVER STOP ABRUPTLY (risk of relapse/myxedema coma); drug interactions (calcium, iron, antacids, phenytoin decrease absorption)
- Levothyroxine dosing adjustment: recheck TSH 4–6 weeks after dose change (long half-life ~7 days, takes weeks for steady state)
Key definitions
Methimazole
Example
Patient with Graves' disease: start ~10 mg TID, monitor CBC for sore throat/fever
Antithyroid drug blocking thyroid hormone synthesis; effect in 4–8 weeks; preferred post–first trimester; agranulocytosis risk.
Propylthiouracil (PTU)
Example
Pregnant patient with hyperthyroidism: PTU ~100 mg TID (safer than methimazole in trimester 1)
Antithyroid drug blocking synthesis + peripheral T4→T3 conversion; preferred in first trimester pregnancy; agranulocytosis risk.
Propranolol (Beta-blocker)
Example
Graves' patient: propranolol 40 mg QID for rapid symptom relief while awaiting antithyroid drug effect
Non-selective beta-blocker; controls tachycardia, tremor, palpitations in hyperthyroidism; also inhibits T4→T3 peripheral conversion.
Desmopressin (DDAVP)
Example
DI patient: DDAVP 10 mcg intranasal BID (can be titrated; watch for water intoxication/hyponatremia)
Synthetic ADH (vasopressin analog); used in central diabetes insipidus; intranasal or SC administration.
Levothyroxine (Synthroid)
Example
Hypothyroid patient: levothyroxine 100 mcg PO once daily on empty stomach, 30 min before breakfast
Synthetic T4; lifelong replacement in hypothyroidism; oral on empty stomach; slow-acting (weeks to steady state).
Calcium Gluconate
Example
Post-thyroidectomy tetany: IV calcium gluconate 10 mL of 10% solution in 50 mL saline over 2–5 min (have ready at bedside)
IV calcium replacement for acute symptomatic hypocalcemia/tetany; do NOT give IM (tissue necrosis).
Diagrams to know
- Antithyroid drug mechanism: blocks thyroid peroxidase → inhibits T3/T4 synthesis
- Beta-blocker mechanism in hyperthyroidism: blocks beta-1 (tachycardia), beta-2 (tremor), + inhibits T4→T3 conversion
Nursing Assessment & Post-Op Priorities
Important facts
- POST-THYROIDECTOMY AIRWAY PRIORITY: keep tracheostomy set, O2, suction AT BEDSIDE (highest risk early post-op)
- POST-THYROIDECTOMY POSITIONING: semi-Fowler's to upright; support head/neck with pillows (prevents tension on suture line)
- POST-THYROIDECTOMY HEMORRHAGE CHECK: inspect BEHIND the neck/under dressing (blood drains posteriorly, not visible from front); gentle palpation; report any oozing/swelling immediately
- POST-THYROIDECTOMY VOICE ASSESSMENT: check voice every 2–4 hrs initially; hoarseness = recurrent laryngeal nerve injury; permanent vs temporary depends on nerve injury severity
- POST-THYROIDECTOMY HYPOCALCEMIA: assess for Chvostek's and Trousseau's signs within 24–72 hrs; tingling, numbness, muscle cramps = early signs; HAVE IV CALCIUM GLUCONATE READY
- POST-THYROIDECTOMY DIET: start soft/cool (throat pain); advance as tolerated; report dysphagia (nerve damage) or difficulty breathing
- POST-PARATHYROIDECTOMY: monitor serum calcium closely (may drop acutely if hypoparathyroidism develops); have calcium gluconate ready; assess for tetany
- SIADH nursing: meticulous I&O, daily weight, strict fluid restriction, even if patient complains of thirst; monitor for hyponatremia signs (confusion, headache, seizures); neuro checks Q1–2H if severe
- DI nursing: open access to water (patient may be desperately thirsty); monitor I&O/specific gravity; teach patient to report signs of DDAVP over-replacement (headache, drowsiness, nausea, weight gain = water intoxication)
- Thyroid storm nursing: continuous cardiac monitoring (watch for AFib, arrhythmias); cooling measures (tepid sponging, cool IV fluids, fans—NOT ice packs); no aspirin (displaces thyroid hormone); monitor temp Q15 min
Key definitions
Chvostek's Sign
Example
Post-thyroidectomy patient: tapping cheek → mouth twitch appears → hypocalcemia suspected
Tap the facial nerve anterior to the ear; positive = facial muscle twitch; indicates neuromuscular hyperexcitability from hypocalcemia.
Trousseau's Sign
Example
Inflate cuff on arm to 200 mmHg for 3 min → wrist/hand goes into spasm → hypocalcemia confirmed
Inflate BP cuff above systolic for 3 minutes; positive = carpal spasm (thumb adduction, finger flexion); indicates hypocalcemia.
Diagrams to know
- Post-thyroidectomy hourly assessment sequence: airway → voice → neck (hemorrhage) → swallowing/throat → hypocalcemia signs
- Calcium gluconate IV administration safety: NEVER IM (tissue necrosis); use central line preferred (peripheral OK but risk of phlebitis); never add to bicarbonate (precipitates)
Must remember
- SIADH = SOAKED (excess ADH → water retention, LOW sodium, concentrated urine, restrict fluids). DI = DRY (deficiency ADH → massive polyuria, HIGH sodium, replace fluids + DDAVP). Opposite problems → opposite management.
- ADH-axis labs are CRITICAL: SIADH shows LOW serum sodium + LOW osmolality with HIGH urine osmolality (inappropriate for serum osmolality). DI shows HIGH serum sodium + HIGH osmolality with LOW urine osmolality. Know which is which or you fail the question.
- Thyroid storm (fever, severe tachycardia, agitation, delirium) = MEDICAL EMERGENCY. Management: cooling (NOT aspirin—displaces hormone), propranolol, PTU, iodine, steroids, continuous monitoring. Myxedema coma (hypothermia, hypotension, respiratory depression) = MEDICAL EMERGENCY. Management: IV levothyroxine, airway support, warm gradually (passive—NOT active vasodilation), glucose, steroids.
- Post-thyroidectomy airway is #1 priority: keep tracheostomy set/O2/suction AT BEDSIDE. Check for hemorrhage BEHIND the neck (not just front). Watch for hoarseness (laryngeal nerve damage) and hypocalcemia/tetany (parathyroid damage—Chvostek's/Trousseau's signs positive). Have calcium gluconate ready.
- Levothyroxine (Synthroid) MUST BE TAKEN: on EMPTY stomach, 30–60 min BEFORE breakfast, same time daily, NEVER stop abruptly (relapse/coma risk). Start LOW & GO SLOW in elderly/cardiac (excess T4 = ↑myocardial O2 demand → angina/arrhythmia). Drug interactions: calcium, iron, antacids impair absorption.
- Antithyroid drugs (methimazole/PTU): effect takes 4–8 weeks (NOT rapid). TEACH PATIENT TO REPORT sore throat, fever, unusual bruising = agranulocytosis (bone-marrow suppression). PTU preferred in FIRST TRIMESTER pregnancy; methimazole after. Iodine (Lugol's/SSKI) MUST BE GIVEN AFTER antithyroid drugs started (not before), diluted, through straw, effect within 24–48 hrs.
- PTH RAISES calcium; calcium & phosphate move OPPOSITE: ↑PTH → ↑Ca + ↓phosphate. ↓PTH → ↓Ca + ↑phosphate. Hyperparathyroidism = high Ca (BONES-STONES-GROANS-MOANS: fractures, stones, GI upset, psychiatric). Hypoparathyroidism = low Ca (TETANY: numbness, Chvostek's/Trousseau's, laryngospasm—airway emergency).
- Hypocalcemia signs (hypoparathyroidism/post-thyroidectomy): tingling (perioral, fingers), muscle cramps, positive CHVOSTEK'S (tap cheek → facial twitch), positive TROUSSEAU'S (BP cuff → carpal spasm), laryngospasm (airway), seizures. Acute tetany → IV CALCIUM GLUCONATE STAT (have ready post-op; never IM = tissue necrosis).
- Thyroid function tests: TSH is most sensitive screening. In primary disease, TSH moves OPPOSITE to hormone level: LOW TSH = hyper, HIGH TSH = hypo (feedback intact). Free T4/T3 confirm; RAIU scan shows uptake pattern (high in Graves').
- NLE loves PAIRED OPPOSITES: SIADH/DI, hyperthyroid/hypothyroid, thyroid storm/myxedema coma, hyperparathyroid/hypoparathyroid. Learn the hormone's function, reason out the signs in EACH DIRECTION, know the LIFE-THREATENING CRISES. Test by covering one side of comparison table and reciting the other.
Last minute tips
- When you see SODIUM DERANGEMENT (hyponatremia/hypernatremia), think ADH: Low Na + concentrated urine = SIADH (fluid restrict + slow correction). High Na + dilute urine = DI (fluid replace + DDAVP). Neuro signs (confusion, seizures) are the RED FLAG that you're running out of time.
- Post-op neck surgery ALWAYS screen for HYPOCALCEMIA: Chvostek's/Trousseau's positive = parathyroid damage. Don't wait for symptoms; prophylactically have calcium ready. Laryngospasm from hypocalcemia can steal the airway—it's a real emergency in the ward.
- 'Slowly correct' sodium in SIADH: The exam loves testing whether you know the RATE of correction (≤8–10 mEq/L per 24 hrs). Over-rapid correction → osmotic demyelination. Over-slow correction → seizures from hyponatremia. Know the Goldilocks zone.
- Levothyroxine timing is SACRED: empty stomach, morning, 30–60 min before food, same time daily. If patient asks 'Can I take it with my vitamins?' → NO. If 'Can I take it at dinner?' → NO. This is a classic NLE trap where students lose points by not knowing the drug timing.
- In thyroid storm, NEVER give aspirin for fever: aspirin displaces thyroid hormone from binding proteins → WORSENS the crisis. Use tepid sponging, cooling blankets, cool IVs. This is a high-yield fact that separates exam passers from those who don't.
Comparison tables
SIADH vs Diabetes Insipidus (ADH Disorders)
| Feature | SIADH | Diabetes Insipidus |
|---|---|---|
| ADH Level | TOO MUCH (excess) | TOO LITTLE (deficiency) or renal unresponsiveness |
| Water Handling | RETAINS water (concentrated urine) | LOSES water (dilute polyuria 3–20 L/day) |
| Serum Na+ | LOW (dilutional hyponatremia <135 mEq/L) | HIGH (hypernatremia >145 mEq/L) |
| Serum Osmolality | LOW (<280 mOsm/kg) | HIGH (>295 mOsm/kg) |
| Urine Osmolality | HIGH (concentrated, inappropriate for low serum osmolality) | LOW (dilute) |
| Urine Specific Gravity | HIGH (>1.020) | LOW (1.002–1.005) |
| Thirst | SUPPRESSED (patient not thirsty despite low Na+) | INTENSE (patient desperately thirsty despite polyuria) |
| Causes | SCLC, meningitis, CNS disorders, drugs (SSRIs, carbamazepine), surgery, pulmonary disease | Central: pituitary surgery, head trauma, tumors. Nephrogenic: lithium, amphotericin, renal disease |
| Primary Management | FLUID RESTRICTION (cornerstone); hypertonic saline for severe hyponatremia; vaptans; correct slowly (≤8–10 mEq/L per 24 hrs) | REPLACE FLUIDS; central DI → DDAVP (desmopressin); nephrogenic → high fluids + NSAIDs/thiazides |
| Acute Complication | Cerebral edema, seizures, coma (from severe hyponatremia <120 mEq/L) | Hypovolemic shock, severe hypernatremia (>160 mEq/L) |
| Memory Hook | SIADH = SOAKED (retains water, low Na+, restrict fluids) | DI = DRY (loses water, high Na+, replace fluids + DDAVP) |
Hyperthyroidism vs Hypothyroidism (Thyroid Hormone Disorders)
| Feature | Hyperthyroidism (Too Much T3/T4) | Hypothyroidism (Too Little T3/T4) |
|---|---|---|
| Metabolism | SPED UP (↑metabolic rate, ↑O2 consumption) | SLOWED DOWN (↓metabolic rate) |
| Weight | LOSS (despite ↑appetite) | GAIN (despite normal/↓appetite) |
| Temperature Tolerance | HEAT INTOLERANCE (diaphoresis, warm moist skin) | COLD INTOLERANCE (prefers warm environment) |
| Heart Rate | TACHYCARDIA, palpitations, AFib, tachyarrhythmias | BRADYCARDIA, slow HR |
| GI Motility | DIARRHEA (speedy transit) | CONSTIPATION (slow transit) |
| Mood/Cognition | NERVOUSNESS, irritability, anxiety, insomnia, tremor | DEPRESSION, lethargy, slowed thinking, cognitive fog |
| Skin | WARM, moist, fine hair; smooth skin | COLD, dry, coarse hair; thin/brittle; myxedema (puffy face) |
| Lab: TSH | LOW (<0.5 mIU/L in primary disease) | HIGH (>5 mIU/L in primary disease) |
| Lab: Free T4/T3 | HIGH (↑T4, ↑T3) | LOW (↓T4, ↓T3) |
| Most Common Cause | Graves' disease (autoimmune; includes exophthalmos + goiter) | Hashimoto's thyroiditis (autoimmune) |
| Main Treatment | Antithyroid drugs (methimazole/PTU), beta-blockers, radioactive iodine, or thyroidectomy | Lifelong levothyroxine (empty stomach, morning, never stop abruptly) |
| CRISIS | THYROID STORM: fever 40–41°C, severe tachycardia, delirium → cool (NOT aspirin), propranolol, PTU, iodine, steroids | MYXEDEMA COMA: hypothermia <32°C, hypotension, respiratory depression, coma → IV levothyroxine, airway support, warm gradually, IV glucose |
Hyperparathyroidism vs Hypoparathyroidism (PTH Disorders)
| Feature | Hyperparathyroidism (Too Much PTH) | Hypoparathyroidism (Too Little PTH) |
|---|---|---|
| PTH Level | HIGH (↑PTH drives hypercalcemia) | LOW (↓PTH allows Ca to fall) |
| Serum Calcium | HIGH (hypercalcemia, >10.5 mg/dL) | LOW (hypocalcemia, <8.5 mg/dL) |
| Serum Phosphate | LOW (PTH excretes phosphate) | HIGH (no PTH to excrete phosphate) |
| Bone Effects | DEMINERALIZATION: osteoporosis, fractures, bone pain | Usually normal (unless prolonged/severe) |
| GI Symptoms | CONSTIPATION, nausea, polyuria (nephrolithiasis), GI ulcers, pancreatitis | Usually none unless symptomatic hypocalcemia |
| Neuro/Muscle | WEAKNESS, fatigue; altered mental status (confusion, mood changes) | TETANY: numbness/tingling, muscle cramps, positive Chvostek's/Trousseau's, laryngospasm, seizures |
| Kidney/Urine | POLYURIA (high urinary calcium), kidney STONES (most common) | Variable (depends on cause) |
| Classic Presentation | BONES (fractures), STONES (nephrolithiasis), GROANS (GI), MOANS (psychiatric) | Acute TETANY post-neck surgery; perioral/finger tingling; carpal spasm |
| Most Common Cause | Parathyroid adenoma or hyperplasia; less common: malignancy (PTHrP), vitamin D excess | Post-thyroidectomy/parathyroidectomy (parathyroid gland damage) |
| Main Treatment | IV saline + loop diuretics (furosemide) → calcium excretion; bisphosphonates/calcitonin; PARATHYROIDECTOMY (definitive) | ACUTE tetany: IV CALCIUM GLUCONATE; chronic: oral calcium + active vitamin D (calcitriol); seizure/laryngospasm precautions |
| CRISIS | HYPERCALCEMIC CRISIS: polyuria/dehydration, cardiac arrhythmias (shortened QT), altered mental status, renal failure | TETANY/LARYNGOSPASM: loss of airway, respiratory failure; seizures |
Thyroid Storm vs Myxedema Coma (Thyroid Emergencies)
| Feature | Thyroid Storm (Thyrotoxic Crisis) | Myxedema Coma (Hypothyroid Crisis) |
|---|---|---|
| Underlying Disease | Poorly controlled HYPERTHYROIDISM (excess T3/T4) | Untreated/decompensated HYPOTHYROIDISM (deficient T3/T4) |
| Precipitant | Infection, surgery, stress, iodine exposure, drug withdrawal (antithyroid) | Cold exposure, infection, sedatives, levothyroxine discontinuation |
| Temperature | HIGH FEVER: 39.5–41°C (hyperpyrexia); can reach dangerous extremes | LOW TEMPERATURE: profound HYPOTHERMIA (<32°C) |
| Cardiovascular | SEVERE TACHYCARDIA (HR 140+), arrhythmias (AFib), hypertension, palpitations, chest pain | PROFOUND BRADYCARDIA, HYPOTENSION, shock |
| Mental Status | AGITATION, delirium, psychosis, confusion, restlessness | LETHARGY, COMA, markedly depressed consciousness |
| GI/Metabolic | Vomiting, diarrhea, hyperglycemia (from stress), increased O2 demand | Constipation, hypoglycemia, decreased O2 consumption, respiratory depression (CO2 retention) |
| Respiratory | Increased breathing from ↑metabolism; pulmonary edema risk | HYPOVENTILATION, respiratory depression, CO2 retention, respiratory failure risk |
| Mortality | HIGH if untreated (can rapidly deteriorate) | HIGH if untreated (often mimics death—may be misdiagnosed as terminal) |
| Management | COOLING (tepid sponging, cool IVs, fans—NOT ice; NOT aspirin), IV fluids, propranolol (beta-blocker), PTU (antithyroid), Lugol's iodine, corticosteroids; treat trigger | IV LEVOTHYROXINE (loading dose 200–500 mcg IV), airway/ventilation support, WARM GRADUALLY (passive; NOT active), IV glucose, IV fluids, corticosteroids; treat trigger |
| Monitoring | Continuous cardiac monitoring (arrhythmia watch), temp Q15 min, neuro checks, labs (TSH, free T4, CBC, glucose) | Continuous monitoring (may mimic brain death—keep resuscitating), temp q30 min, slow rewarming, labs (TSH, free T4, glucose, cortisol) |
Diagrams
Endocrine Axis: Pituitary-Thyroid-Parathyroid Overview
Mind map showing the three major endocrine axes covered in this chapter: posterior pituitary (ADH/water balance), anterior pituitary (TSH/thyroid hormone), and parathyroid (PTH/calcium regulation). Shows 'too much vs too little' for each, with key signs and treatments.
Hyponatremia vs Hypernatremia Differential: ADH Perspective
Flowchart algorithm for differentiating SIADH from diabetes insipidus using sodium and urine osmolality. Critical for exam: shows how to work up hyponatremia vs hypernatremia using urine osmolality as the discriminator.
Post-Thyroidectomy Immediate Assessment (First 24 Hours)
Sequential assessment flowchart for the critical first 24 hours post-thyroidectomy. Prioritizes airway (top threat), then hemorrhage, laryngeal nerve function, and hypocalcemia. Red boxes highlight emergencies requiring immediate physician notification.
Levothyroxine: Absorption & Timing Critical (Exam Trap)
Flowchart emphasizing the critical but often-missed levothyroxine timing rule. Shows how incorrect timing (taking with food/calcium) is misdiagnosed as non-compliance or need for dose increase. This is a common NLE trap.
Calcium Homeostasis: PTH Feedback Loop
State diagram showing normal calcium homeostasis (feedback loop) and what happens when PTH is absent (hypoparathyroidism) or excess (hyperparathyroidism). Illustrates why hypocalcemia triggers PTH release and why surgery disrupts this.
Common Causes of Hypothyroidism: Know Your Epidemiology
Pie chart showing that Hashimoto's autoimmune thyroiditis accounts for ~90% of hypothyroidism cases. Post-ablation/post-surgical causes are important to know for NLE but less common. This helps prioritize study time.