THE MECHANISM
The GH-IGF-1 Axis
Tap each node to see what it does and what goes wrong when it breaks
Step 1 · Hypothalamus
GHRH
Growth Hormone Releasing Hormone
GHRH is the trigger. When your body needs to grow (or is stressed), the hypothalamus fires GHRH. Think of it like the hypothalamus sending a text to the pituitary saying "turn on the growth factory." Somatostatin is the hypothalamus's "stop" text, sent after growth occurs.
Board angle: Octreotide works as a somatostatin analogue, which is exactly why it shuts down GH release. It mimics the "stop" signal.
Board angle: Octreotide works as a somatostatin analogue, which is exactly why it shuts down GH release. It mimics the "stop" signal.
↓
Step 2 · Anterior Pituitary
GH
Growth Hormone (Somatotropin)
The pituitary releases GH in pulses, mainly after the first REM cycle of sleep. This is why kids grow at night.
In gigantism and acromegaly, a somatotroph adenomaA benign tumor of the growth hormone-secreting cells in the anterior pituitary. Autonomous = it ignores all feedback signals. keeps firing GH nonstop regardless of what the hypothalamus says. It's gone rogue. No off switch.
Why the glucose test works: Normally, eating glucose tells GH to shut up (sugar means you're fed, not stressed). In a GH-secreting adenoma, glucose suppression fails because the tumor doesn't listen.
In gigantism and acromegaly, a somatotroph adenomaA benign tumor of the growth hormone-secreting cells in the anterior pituitary. Autonomous = it ignores all feedback signals. keeps firing GH nonstop regardless of what the hypothalamus says. It's gone rogue. No off switch.
Why the glucose test works: Normally, eating glucose tells GH to shut up (sugar means you're fed, not stressed). In a GH-secreting adenoma, glucose suppression fails because the tumor doesn't listen.
↓
Step 3 · Liver
IGF-1
Insulin-like Growth Factor 1 (Somatomedin)
GH tells the liver to make IGF-1. IGF-1 is the actual growth signal that reaches bones, tendons, and muscles.
Why screen with IGF-1 and not GH? GH has a half-life of about 20 minutes and pulses unpredictably. One random GH level tells you almost nothing. IGF-1 is stable and reflects the running average of GH over days. If IGF-1 is elevated, GH has been chronically high.
Liver disease caveat: A cirrhotic liver can't make IGF-1 even with high GH. So a patient with liver disease can have low IGF-1 despite elevated GH. Board trap incoming.
Why screen with IGF-1 and not GH? GH has a half-life of about 20 minutes and pulses unpredictably. One random GH level tells you almost nothing. IGF-1 is stable and reflects the running average of GH over days. If IGF-1 is elevated, GH has been chronically high.
Liver disease caveat: A cirrhotic liver can't make IGF-1 even with high GH. So a patient with liver disease can have low IGF-1 despite elevated GH. Board trap incoming.
↓
Step 4 · Growth Plates
Bone & Soft Tissue
Where size happens
In children (open growth plates): IGF-1 drives linear growth. The long bones get longer. Kid becomes extremely tall. This is gigantism.
In adults (closed growth plates): The bones can't get longer. Instead they get wider. Hands and feet expand. Jaw protrudes. Forehead pushes forward. Organs enlarge. This is acromegaly.
The hat and shoes clue: "My hat doesn't fit anymore" = skull/jaw expanding. "I went up a shoe size" = feet widening. Classic board-exam signal for acromegaly.
In adults (closed growth plates): The bones can't get longer. Instead they get wider. Hands and feet expand. Jaw protrudes. Forehead pushes forward. Organs enlarge. This is acromegaly.
The hat and shoes clue: "My hat doesn't fit anymore" = skull/jaw expanding. "I went up a shoe size" = feet widening. Classic board-exam signal for acromegaly.
Tap any node to expand the detail. Each step matters for the quiz later.
Board Trap: Gigantism vs Acromegaly is ONLY About Growth Plate Status
The cause is identical (usually a pituitary adenoma). The diagnosis workup is identical. The treatment is identical. The only difference is whether the epiphyseal plates are open or closed when GH excess starts. Open plates = gigantism (linear growth). Closed plates = acromegaly (widening growth only). Some people get GH excess as a teen and end up with BOTH: they're very tall AND have acromegalic features.
🔑
One disease, two names, one difference. Growth plates open = Gigantism. Growth plates closed = Acromegaly. The tumor is the same. The workup is the same. The plates decide the phenotype.
QUICK REFERENCE
The Six Players
Tap each card to flip it. Board-critical facts on the back.
Before Growth Plate Fusion
Gigantism
GH excess in childhood
Linear growth explodes. The bones get longer, not just wider.
tap to flip
The Setup
Somatotroph adenoma secreting GH before epiphyseal plates close. IGF-1 drives linear bone growth. Long bones lengthen unrestricted. Child grows far beyond normal height trajectory.
Key Features
- Height at or above 99th percentile
- Advanced bone age on X-ray
- Broad hands and feet (soft tissue + bone)
- Sweating, elevated glucose
- Normal Tanner staging (not precocious puberty)
key pattern: Open growth plates + GH excess = linear growth = gigantism. Closed plates + same excess = only widening = acromegaly.
After Growth Plate Fusion
Acromegaly
GH excess in adulthood
Bones widen instead of lengthen. Ring and shoe sizes increase. Jaw juts forward.
tap to flip
The Setup
Same root cause as gigantism. But fused epiphyses can't lengthen. GH and IGF-1 drive periosteal bone widening and soft tissue overgrowth instead. Slow, insidious onset over years.
Key Features
- Shoe/ring size increasing (classic board clue)
- Jaw protrusion (prognathism), widened nose
- Carpal tunnel syndrome (bilateral)
- Cardiomegaly (#1 cause of death if untreated)
- Sleep apnea, colon polyps, diabetes
key pattern: "My hat and shoes don't fit anymore" = acromegaly. Insidious, diagnosed late. Always post-epiphyseal closure.
Primary Mediator
IGF-1
Insulin-like Growth Factor 1
The real growth signal. GH just tells the liver to make it. IGF-1 does all the work.
tap to flip
Why IGF-1 Matters More Than GH
GH has a 20-minute half-life and pulses unpredictably throughout the day. A single random GH level is nearly useless. IGF-1 is stable and reflects the running average of GH over days.
Board Logic
- Screen with IGF-1 first, not random GH
- Elevated IGF-1 = chronic GH excess
- Confirm with oral glucose suppression test
- Liver disease caveat: cirrhosis lowers IGF-1 even with high GH
key pattern: IGF-1 is the screening test. Never use a random GH level to screen. Random GH can be normal even in a GH-secreting tumor.
Root Cause
Somatotroph Adenoma
GH-secreting pituitary tumor
Autonomous. Ignores all feedback. GH production doesn't stop regardless of glucose, IGF-1, or somatostatin.
tap to flip
The Tumor
Located in the anterior pituitary. Grows silently. Macroadenomas (>1cm) compress the optic chiasm above → bitemporal hemianopia. Compresses normal pituitary → hypopituitarism.
Key Features
- Bitemporal hemianopia (chiasm compression)
- Headaches (dural pressure)
- Hypopituitarism if large enough
- Order MRI AFTER biochemical confirmation
key pattern: Bitemporal hemianopia + tall stature + sweating = pituitary adenoma compressing the optic chiasm from below. Check IGF-1 first, MRI second.
Acromegaly Complications
The Long Game
What kills if untreated
Cardiomegaly is the #1 cause of death. But there are several other complications that make it to boards.
tap to flip
High-Yield Complications
- Cardiomegaly (IGF-1 on cardiomyocytes) = #1 killer
- Carpal tunnel syndrome (median nerve compression)
- Sleep apnea (macroglossia, soft tissue expansion)
- Diabetes mellitus (GH is anti-insulin)
- Colon polyps / colonoscopy screening required
- Hyperhidrosis tracks with disease activity
key pattern: Cardiomegaly is the top killer in untreated acromegaly. Normalize IGF-1 = protect the heart. Sweating that gets worse = disease not controlled.
Treatment Ladder
Surgery to Radiation
4-step management
Transsphenoidal surgery first. Then octreotide. Then pegvisomant. Radiation is the last resort.
tap to flip
The Escalation Ladder
- 1. Transsphenoidal surgery (cure when it works)
- 2. Octreotide (somatostatin analogue, suppresses GH release)
- 3. Pegvisomant (GH receptor blocker, different mechanism)
- 4. Radiation (last resort, slow, risk of hypopituitarism)
Critical Distinction
Octreotide suppresses GH secretion. Pegvisomant blocks GH action at the receptor. Different points of attack.
key pattern: Surgery fails → octreotide. Octreotide fails → pegvisomant. Never jump to radiation when medical options remain.
RECOGNITION
What They Look and Feel Like
Gigantism vs acromegaly side by side, and what connects them both
Gigantism
GH excess BEFORE epiphyseal closure
📷 Coarsened facial features · tap to expand
| Feature | What You See | Why |
|---|---|---|
| Height | 99th percentile or higher | Open growth plates respond to IGF-1, bones lengthen |
| Bone age | Advanced (bone age > chronologic age) | Excess GH/IGF-1 accelerates ossification |
| Facial bones | Frontal bossing, jaw protrusion | Flat bones of skull still respond to GH even with open plates |
| Hands/feet | Broad, doughy | Soft tissue hypertrophy from IGF-1 |
| Glucose | Elevated (138 mg/dL in stem) | GH is catabolic, drives gluconeogenesis, causes insulin resistance |
🔥The dead giveaway: tall kid + broad hands + sweating + elevated glucose + advanced bone age. That cluster on a board exam is gigantism until proven otherwise.
Acromegaly
GH excess AFTER epiphyseal closure
📷 Enlarged hands · tap to expand
| Feature | What You See | Why |
|---|---|---|
| Height | Normal (plates already closed) | Can't lengthen what's already fused |
| Hands/feet | Ring/shoe size increasing over years | Periosteal bone widening + soft tissue expansion |
| Face | Jaw juts forward (prognathism), widened nose | Membranous bone continues to respond to GH |
| Carpal tunnel | Bilateral hand numbness/tingling | Soft tissue overgrowth compresses median nerve |
| Heart | CardiomegalyThe #1 cause of death in untreated acromegaly. The heart muscle (also soft tissue) hypertrophies, leading to heart failure over decades. | Most dangerous long-term complication. Kills before diabetes does. |
💡"My hat and shoes don't fit anymore." Classic board setup for acromegaly. If you also see Paget's mentioned, distinguish: Paget's = high alk phos + sclerotic bones + older patient. GH excess = normal alk phos + soft tissue growth + young-to-middle age.
Features Shared by Both
Same root cause, same metabolic wreck
📷 Pituitary macroadenoma on MRI · tap to expand
Metabolic Effects
- Insulin resistance (GH is anti-insulin)
- Glucose intolerance or frank diabetes
- Dyslipidemia
Autonomic / Secretory
- Hyperhidrosis (excessive sweating)
- Oily skin (sebaceous gland overgrowth)
- Fatigue, weakness
Mass Effects (Adenoma)
- Headaches (pressure)
- Bitemporal hemianopia (optic chiasm compression)
- Hypopituitarism if big enough
Organomegaly
- Cardiomegaly (biggest killer)
- Visceromegaly (liver, spleen, kidney)
- Macroglossia (enlarged tongue)
- Thyroid enlargement
Board Trap: Sweating is Not Just "A Symptom"
Hyperhidrosis (excessive sweating) is one of the most reliable clinical markers of active GH excess and is actually used to track disease activity. If a patient with treated acromegaly says their sweating has gotten worse, that's a red flag for recurrence or inadequate control. The boards love this as a "symptom that tracks with disease activity."
THE WORKUP
How to Diagnose It
The boards test whether you know the order. Get the order wrong, get it wrong.
Here's the trap most students fall into: they order an MRI first. That's wrong. You confirm the hormone problem before you go hunting for the tumor. Why? Because a random GH level is useless (it pulses all day), and an MRI without biochemical confirmation is just expensive photography.
DIAGNOSTIC SEQUENCE
1
Serum IGF-1Also called somatomedin C. Stable marker that reflects average GH secretion over days. High IGF-1 = chronic GH excess. This is your screening test. level
Screening test. If elevated, proceed. Do NOT order a random GH level, it fluctuates too much to be useful.
2
Oral Glucose Suppression Test 🔑100g glucose, check GH at 1-2 hours. Normal: GH suppresses below 5 ng/mL. GH-producing tumor: GH stays high because the adenoma doesn't care about glucose.
CONFIRMATORY test. Give 100g oral glucose. Measure GH at 1-2 hours. Normal suppression = GH falls below 5 ng/mL. Failure to suppress = GH-secreting adenoma confirmed.
3
MRI of the pituitary gland
Only AFTER biochemical confirmation. This localizes the adenoma. Most are macroadenomas (>1cm) by the time symptoms appear because growth is slow.
⚠️
Why does the oral glucose suppression test work as a confirmation test? You already know about the feedback loop: when blood sugar rises, GH should shut off (you're fed, not stressed, so stop growing). A normal pituitary responds to glucose and kills GH secretion. A somatotroph adenoma doesn't get that memo. It just keeps pumping. GH stays high. Diagnosis confirmed.
DIAGNOSTIC REASONING
Walk Through the Workup
A patient walks in with signs of GH excess. Walk through each decision point.
Step 1: A patient has extreme tall stature, broad doughy hands, and sweating. You suspect GH excess. What is your first test?
Exactly. IGF-1 is the screening test. GH pulses unpredictably with a 20-minute half-life. One random level can be normal even in a GH-producing tumor. IGF-1 reflects the running average of GH over days. Screen with IGF-1. Confirm later.
Not quite. Random GH is the classic trap. It pulses and can look normal even with a GH-secreting adenoma. Imaging before biochemical confirmation is expensive and non-specific. The right first move is IGF-1: stable, reliable, reflects chronic GH status.
THE FIX
Treatment Algorithm
Tap each step to see the mechanism and when you'd use it
First Line
Transsphenoidal Surgery
Remove the adenoma. The cure, when it works.
The anterior pituitary is tucked right behind the sphenoid sinus, which is why surgeons go through the nose ("transsphenoidal") rather than cracking open the skull. It's elegant: no brain retraction needed for small tumors.
When it works: Microadenomas (<1cm) have cure rates above 80-90%. Macroadenomas are harder to fully resect.
Success check: Post-op IGF-1 + oral glucose suppression test. If IGF-1 normalizes and GH suppresses, you're cured. If not, move to step 2.
Board pearl: Always ask "what confirms surgical cure?" Answer: normal IGF-1 + GH suppression below 1 ng/mL on OGTT.
When it works: Microadenomas (<1cm) have cure rates above 80-90%. Macroadenomas are harder to fully resect.
Success check: Post-op IGF-1 + oral glucose suppression test. If IGF-1 normalizes and GH suppresses, you're cured. If not, move to step 2.
Board pearl: Always ask "what confirms surgical cure?" Answer: normal IGF-1 + GH suppression below 1 ng/mL on OGTT.
Second Line (Medical)
Octreotide (Somatostatin Analogue)
When surgery doesn't fully work. Mimics somatostatin to suppress GH release.
Remember the feedback loop: somatostatin from the hypothalamus tells the pituitary to stop making GH. Octreotide is a synthetic somatostatin that works longer and more powerfully.
The adenoma STILL has somatostatin receptors (unlike its resistance to glucose). So octreotide actually works on tumor cells to suppress GH secretion.
Also used for: pre-op tumor shrinkage, patients who can't have surgery, carcinoid syndrome, glucagonoma, insulinoma, portal hypertension (remember for boards).
Side effects: GI upset (nausea, diarrhea), cholelithiasis (it slows gallbladder emptying), and bradycardia.
The adenoma STILL has somatostatin receptors (unlike its resistance to glucose). So octreotide actually works on tumor cells to suppress GH secretion.
Also used for: pre-op tumor shrinkage, patients who can't have surgery, carcinoid syndrome, glucagonoma, insulinoma, portal hypertension (remember for boards).
Side effects: GI upset (nausea, diarrhea), cholelithiasis (it slows gallbladder emptying), and bradycardia.
Third Line (Refractory)
Pegvisomant (GH Receptor Antagonist)
Blocks GH from binding its receptor. Different mechanism from octreotide.
Pegvisomant is a GH receptor blocker. Instead of suppressing GH secretion, it blocks GH from doing anything at all. Think of it like changing the locks on the door.
Why third line? It's expensive, requires daily injections, and because it blocks GH action rather than GH release, it doesn't shrink the tumor. You have to keep monitoring for tumor growth with MRI.
Board distinction: Octreotide suppresses GH release. Pegvisomant blocks GH action. Both lower IGF-1. Different points of attack.
Break it down: If the question says "IGF-1 is still elevated after surgery and octreotide," the answer is pegvisomant.
Why third line? It's expensive, requires daily injections, and because it blocks GH action rather than GH release, it doesn't shrink the tumor. You have to keep monitoring for tumor growth with MRI.
Board distinction: Octreotide suppresses GH release. Pegvisomant blocks GH action. Both lower IGF-1. Different points of attack.
Break it down: If the question says "IGF-1 is still elevated after surgery and octreotide," the answer is pegvisomant.
Last Resort
Radiation Therapy
Slowly destroys remaining tumor cells. Takes years. Hypopituitarism risk.
Radiation works by killing adenoma cells, but GH and IGF-1 drop very slowly over years (sometimes a decade). During that time you still need medical therapy.
The big risk: Hypopituitarism. Radiation isn't precise enough to spare the rest of the pituitary. Patients often need replacement therapy for thyroid, cortisol, and sex hormones afterward.
Stereotactic radiosurgery (Gamma Knife) is more precise and has a slightly better profile, but still carries hypopituitarism risk.
The big risk: Hypopituitarism. Radiation isn't precise enough to spare the rest of the pituitary. Patients often need replacement therapy for thyroid, cortisol, and sex hormones afterward.
Stereotactic radiosurgery (Gamma Knife) is more precise and has a slightly better profile, but still carries hypopituitarism risk.
💥
Treatment order to memorize: Surgery (cure) → Octreotide (suppress GH release) → Pegvisomant (block GH receptors) → Radiation (last, slow, risky). The boards love asking which drug to add when surgery didn't fully work.
GAME TIME
Eliminate the Imposters
One tall teenager. Four possible diagnoses. Clues will eliminate them one by one. You click who's out.
A 15-year-old is brought in for "just growing too fast." You have four working diagnoses. Each clue eliminates one. Click the card you think the clue rules out. Be wrong and you'll hear about it.
Familial Tall Stature
Both parents are tall
Marfan Syndrome
Fibrillin-1 mutation
Precocious Puberty
Early sex hormone surge
Gigantism (GH Excess)
Pituitary adenoma
Loading first clue...
PROVE IT
Clinical Vignettes
Six patients walk in. All of them are about to test you. Don't let them win.