Gastroparesis is one of those Step 1 topics that looks deceptively simple (“delayed gastric emptying”) until a vignette forces you to separate it from mechanical obstruction, dumping syndrome, and functional dyspepsia—often in a diabetic patient with vague nausea and early satiety. If you can explain why the stomach won’t move, how to prove it, and what meds actually help (and which ones worsen it), you’re in great shape for test day.
What Gastroparesis Is (and Is Not)
Definition:
Gastroparesis = delayed gastric emptying in the absence of mechanical obstruction.
What it is NOT (classic Step traps):
- Mechanical gastric outlet obstruction (e.g., malignancy, pyloric stenosis): delayed emptying with a physical blockage.
- Dumping syndrome: rapid gastric emptying (often post-gastrectomy), classically with postprandial symptoms.
- Small bowel obstruction: more diffuse abdominal distension, obstipation, air-fluid levels; not isolated gastric emptying dysfunction.
High-Yield Pathophysiology
Normal gastric emptying requires:
- Antral contraction (grinding)
- Coordinated pyloric relaxation
- Antroduodenal coordination
- Enteric nervous system signaling, including vagal input
- Interstitial cells of Cajal (GI pacemaker cells)
In gastroparesis, the key issue is impaired neuromuscular function—often due to autonomic (vagal) neuropathy or damage to pacemaker/enteric signaling.
Major mechanisms (Step-friendly)
- Diabetes mellitus: chronic hyperglycemia → autonomic neuropathy (vagal) ± impaired nitric oxide signaling → poor antral contraction and pyloric dysfunction.
- Postsurgical: vagal nerve injury (e.g., fundoplication, esophagectomy, gastric surgery) → decreased gastric motility.
- Medications: drugs that slow gastric motility (opioids, anticholinergics, GLP-1 agonists).
- Systemic disease: hypothyroidism, scleroderma (can affect GI motility broadly), Parkinson disease.
- Idiopathic: common in practice, still fair game for exams.
Why hyperglycemia matters (very HY)
Acute hyperglycemia can worsen gastric emptying even without longstanding neuropathy. On exams, this supports:
- Tight glucose control as part of treatment
- Delayed emptying symptoms being worse with poor glycemic control
Etiologies & Associations (High-Yield)
| Cause | Clues in vignette | Mechanism |
|---|---|---|
| Diabetes (most tested) | Longstanding DM, neuropathy, retinopathy; postprandial nausea/early satiety | Autonomic neuropathy → impaired motility |
| Postsurgical vagal injury | History of upper abdominal surgery; early satiety/vomiting | Loss of vagal stimulation |
| Medications | Opioids, anticholinergics, GLP-1 agonists (semaglutide, etc.) | Decreased GI motility |
| Parkinson disease | Tremor/rigidity + GI symptoms | Autonomic dysfunction |
| Hypothyroidism | Constipation, weight gain, cold intolerance | Slowed GI motility |
| Scleroderma | Dysphagia/GERD + bloating | Smooth muscle atrophy/fibrosis + dysmotility |
First Aid cross-reference (conceptual):
- Diabetes complications → autonomic neuropathy → gastroparesis
- Opioids/anticholinergics → decreased GI motility
- Scleroderma → GI dysmotility (Exact page numbers vary by edition, but these associations are explicitly covered in the diabetes and GI motility sections.)
Clinical Presentation (What Shows Up in Vignettes)
Classic symptoms
- Nausea and vomiting (often of undigested food hours after meals)
- Early satiety
- Postprandial fullness
- Bloating
- Epigastric pain (variable)
- Weight loss (in severe cases)
Physical exam / labs (supportive, not diagnostic)
- Epigastric distension, succussion splash (nonspecific)
- In diabetics: wide glucose swings due to unpredictable absorption
Complications (HY)
- Dehydration, electrolyte abnormalities (vomiting)
- Malnutrition/weight loss
- Bezoar formation (retained food → concretion)
- Erratic glycemic control (especially in insulin-dependent diabetics)
Diagnosis: Stepwise and Testable
Step 1: Exclude mechanical obstruction
Because gastroparesis is defined by absence of obstruction, the first move is often:
- Upper endoscopy (EGD) or
- Upper GI series / imaging if obstruction suspected (depending on vignette)
Red flags that push obstruction higher:
- Progressive symptoms, GI bleeding, severe weight loss, older age, palpable mass
- Persistent non-bilious vomiting with visible obstruction clues
Step 2: Confirm delayed gastric emptying
Gold standard (most testable):
Gastric emptying scintigraphy (radio-labeled meal; delayed emptying at set time points).
Other tests you may see:
- 13C breath test (less common in exam questions)
- Wireless motility capsule (more Step 2-ish; less classic)
High-yield vignette language
- “Delayed emptying on gastric scintigraphy”
- “No obstruction on endoscopy”
- “Longstanding diabetes” + “early satiety, nausea, vomiting”
Treatment: What Actually Helps (and What Hurts)
Management is typically step-up: lifestyle → meds → procedures.
1) Lifestyle & nutrition (always safe, often asked)
- Small, frequent meals
- Low-fat, low-fiber diet
- Fat slows gastric emptying
- Fiber increases bezoar risk
- Liquid calories can be easier to empty than solids
- Optimize glucose control (major in diabetics)
- Stop offending drugs if possible:
- Opioids
- Anticholinergics
- Consider impact of GLP-1 agonists (they slow gastric emptying)
2) Prokinetic medications (core Step pharm)
Metoclopramide
- Mechanism: D2 antagonist (also some 5-HT4 agonism) → ↑ ACh release in enteric NS → ↑ gastric motility
- Also antiemetic via D2 blockade in CTZ
- High-yield adverse effects: extrapyramidal symptoms, tardive dyskinesia, hyperprolactinemia
Erythromycin
- Mechanism: motilin receptor agonist → increased migrating motor complex activity
- Limitation: tachyphylaxis (loses effect over time), GI cramping, QT risk
Domperidone (less emphasized in US due to access/regulatory issues)
- Peripheral D2 antagonist; fewer CNS side effects (doesn’t cross BBB well)
3) Antiemetics (symptom control; doesn’t fix emptying)
- Ondansetron, prochlorperazine, etc. (vignette-dependent)
4) Refractory cases (Step 2-style escalation)
- Gastric electrical stimulation (selected patients)
- Enteral feeding via jejunostomy if severe malnutrition
- Endoscopic/surgical pyloromyotomy in select cases (emerging; not classic Step 1 but fair conceptually)
HY Differentials You Must Separate from Gastroparesis
Gastroparesis vs Gastric outlet obstruction
| Feature | Gastroparesis | Gastric outlet obstruction |
|---|---|---|
| Definition | No mechanical obstruction | Mechanical blockage present |
| Key test | Gastric emptying scintigraphy | EGD / imaging shows obstruction |
| Classic causes | Diabetes, vagal injury, meds | Cancer, PUD scarring/edema |
| Vomiting | Undigested food, chronic | Can be severe; may have visible obstruction signs |
Gastroparesis vs Dumping syndrome
| Feature | Gastroparesis | Dumping syndrome |
|---|---|---|
| Emptying | Delayed | Rapid |
| Typical setting | DM, neuropathy, meds | Post-gastrectomy/bypass |
| Symptoms | Early satiety, nausea, vomiting | Early: diarrhea, cramping, vasomotor; Late: hypoglycemia |
USMLE High-Yield Fact Bank (Rapid Review)
- Gastroparesis = delayed gastric emptying without obstruction.
- Most classic association: diabetes → autonomic (vagal) neuropathy.
- Gold standard test: gastric emptying scintigraphy.
- Always rule out mechanical obstruction first (EGD/imaging).
- Treatment pearls:
- Small frequent meals; low fat/low fiber
- Metoclopramide (D2 antagonist) → watch for EPS/tardive dyskinesia
- Erythromycin (motilin agonist) → tachyphylaxis
- Optimize glucose; stop opioids/anticholinergics/meds that slow motility
- Complications: bezoars, malnutrition, dehydration, erratic glycemic control.
How Gastroparesis Gets Tested (Vignette Pattern)
A very typical question stem:
- Patient with longstanding diabetes
- Early satiety + nausea/vomiting (often after meals)
- Possibly wide glucose variability
- Endoscopy shows no obstruction
- Next step / best test: gastric emptying scintigraphy
- Best initial management: dietary changes + glucose control
- Best medication: metoclopramide (with EPS warning) or erythromycin
If the vignette mentions chronic opioid use or anticholinergic meds, they’re often fishing for:
- Medication-induced gastroparesis and the importance of discontinuation