Verification & Expansion of Your Migraine Pathophysiology Summary

Section 1 - Triggering Phase ("Hyperexcitable Brain") ✅ Mostly Accurate

"It seems probable that there is not a single 'migraine generator' shared by all people with migraine and that there is not a single 'migraine generator' within individuals from attack to attack."

Section 2 - Cortical Spreading Depression (CSD) ✅ Accurate, with important caveats

• Bradley & Daroff: "2-4 mm/min"
• Adams & Victor: "2.2-3 mm/min"
• Guyton & Hall: consistent with ~3 mm/min

"It is debated whether or not CSD can lead to activation of the trigeminocervical system and thus trigger the headache phase." - Bradley & Daroff

Section 3 - Trigeminovascular System Activation ✅ Accurate, Expandable

• Trigeminal nerve supplying meninges and large cerebral vessels ✅
• Release of CGRP, Substance P, Neurokinin A ✅
• Resulting vasodilation and sterile neurogenic inflammation ✅

"Activation of these fibers releases substance P, CGRP, and other peptides into the vessel wall, which serves to sensitize the trigeminal system to the pulsatility of cranial vessels, and to increase their permeability, thereby promoting an inflammatory response."

Section 4 - Central Sensitization ✅ Accurate

"Recurrent and/or prolonged activation of the trigeminocervical system can lead to peripheral and central sensitization. Sensitized neurons have lower thresholds for activation, increased spontaneous activity, and receptive field expansion. Approximately three-fourths of people with migraine have evidence of cutaneous allodynia during a migraine attack."

Section 5 - Brainstem Dysfunction ✅ Accurate, with additions

"Plasma and platelet concentrations of 5HT vary with different phases of the migraine attack. Urinary concentrations of 5HT and its metabolites are elevated during most migraine attacks. Migraine may be precipitated by agents (e.g., reserpine and fenfluramine) that release 5HT from intracellular storage sites."

Neurotransmitter Table - Corrections & Additions

Section on Triptans - Accurate but Incomplete

"One hypothesis... activation of 5HT1B/1D receptors may cause constriction of intracranial blood vessels... An alternative hypothesis proposes that both 5HT1B and 5HT1D receptors serve as presynaptic autoreceptors that block the release of neurotransmitter or proinflammatory neuropeptides at nerve terminals in the perivascular space."

Points Missing From Your Summary

Summary of Accuracy

• Bradley and Daroff's Neurology in Clinical Practice, block26
• Adams and Victor's Principles of Neurology 12th ed., block2
• Goodman & Gilman's The Pharmacological Basis of Therapeutics, block4
• Guyton and Hall Textbook of Medical Physiology, block6
• Recent PubMed reviews: PMID 38887982 (PACAP treatments, 2024), PMID 41087022 (sex differences in migraine, 2025)

• Color-coded cascade: Trigger → Brain Hyperexcitability → CSD → Trigeminovascular Activation → Central Sensitization → Migraine Headache
• Each step has its own color and key bullet points

• Prodrome, Aura, Headache, Postdrome - each with clinical details

• 8 mediators including CGRP, Serotonin, NO, Dopamine, Glutamate, SP, NKA, and PACAP - with roles and clinical notes (gepants, anti-CGRP mAbs, etc.)

• Written in plain language ("The brain fires first, not the blood vessels")
• Each step has a "Think of it as..." analogy (e.g., Aura = "an electrical storm in the brain")
• Color-coded numbered steps with arrows

• Each phase explained in simple what happens / what you feel format
• Chemicals table uses everyday language ("Makes blood vessels swell + sends pain signals")
• Triptans box explains the two mechanisms simply with numbered points

• 8 key exam facts in icon + short phrase format - perfect for last-minute revision
• e.g. "CSD = basis of AURA", "Triptans work best taken EARLY", "3x more common in women"

• No dense jargon (no "oligemia", "perisynaptic", etc.)
• No complex debate text
• Plain analogies used throughout

Pathophysiology of Migraine — Simplified for UG Students

First, the Big Picture

"Migraine is primarily a disorder of the nervous system — the brain dysfunction comes first. Blood vessel changes are secondary, not the cause." — Harrison's Principles of Internal Medicine 22e

Step 1 — Why Some People Get Migraine: The Hyperexcitable Brain

"Migraineurs are particularly sensitive to environmental and sensory stimuli; migraine-prone patients do not habituate easily to sensory stimuli."

• First-degree relatives of a migraineur have 2-4x higher risk of also getting migraines
• In a specific type called Familial Hemiplegic Migraine (FHM), mutations are found in ion channel genes (CACNA1A, ATP1A2, SCN1A) — these genes control how excitable brain cells are
• In most common migraine, the genetics are more complex but the principle is the same: a lower threshold for brain activation

Step 2 — The Trigger Fires the Starting Gun

Step 3 — The Prodrome ("Warning Phase") — Hours Before the Headache

• Yawning excessively
• Craving sweet food
• Mood swings (irritable or euphoric)
• Fatigue, drowsiness
• Needing to urinate more

"The sensory sensitivity that is characteristic of migraine is probably due to dysfunction of monoaminergic and other sensory control systems located in the brainstem and hypothalamus."

Step 4 — Cortical Spreading Depression: The Electrical Storm (Causes the Aura)

1. A sudden intense burst of neuronal firing starts in the occipital cortex (back of the brain - the visual area)
2. This wave of depolarization spreads forward across the cortex at a rate of 2-4 mm per minute (very slow compared to normal nerve signals)
3. Behind the wave, neurons go quiet (depression/suppression)
4. Blood flow initially increases briefly, then decreases (oligemia)
5. The whole wave does not follow blood vessel boundaries - ruling out simple vasospasm as the cause

• Positive symptoms first (brain firing): Flashing lights, zig-zag lines, sparkles - called a "scintillating scotoma"
• Negative symptoms follow (brain suppression): Blind spots, numbness, difficulty speaking
• Symptoms march across the visual field slowly over ~20-30 minutes (mirroring the 2-4 mm/min spread rate)

Important: CSD clearly explains the AURA. Whether CSD directly triggers the headache phase is still debated in the literature (Bradley & Daroff, 2023).

Step 5 — Trigeminovascular Activation: Where the Pain Comes From

"The innervation of the large intracranial vessels and dura mater by the trigeminal nerve is known as the trigeminovascular system."

The Trigeminal Nerve is the Pain Nerve of the Head

• The meninges (coverings of the brain)
• Large cerebral blood vessels
• The dura mater

What Happens When They Fire?

• Blood vessels swell and dilate
• Plasma proteins leak out of vessels into surrounding tissue
• Inflammatory soup forms around the meninges
• The meninges become swollen and sensitive

"CGRP receptor antagonists, gepants, have now been shown to be effective in the acute and preventive treatment of migraine, and four monoclonal antibodies to CGRP, or its receptor, have been shown to be effective in migraine prevention."

Step 6 — Central Sensitization: Why Everything Becomes Painful

"Recurrent and/or prolonged activation of the trigeminocervical system can lead to peripheral and central sensitization. Sensitized neurons have lower thresholds for activation, increased spontaneous activity, and receptive field expansion."

1st order neuron sensitized → trigeminal nerve endings
        ↓
2nd order neuron sensitized → trigeminal nucleus caudalis
        ↓  (allodynia begins here - scalp tenderness)
3rd order neuron sensitized → thalamus + cortex
        ↓  (whole-body allodynia, photophobia, phonophobia)

• Combing hair or wearing glasses hurts during an attack
• Bright light becomes unbearable (photophobia)
• Normal sounds are painful (phonophobia)
• Smells become overwhelming (osmophobia)

Clinical importance: Once allodynia (central sensitization) is established, triptans become LESS effective. This is why early treatment is emphasised.

Step 7 — Brainstem Neurotransmitter Changes

"In the late 1950s, methysergide was suggested to antagonize certain peripheral actions of 5-HT and was introduced as a migraine preventive... The triptans were designed to stimulate selectively subpopulations of 5-HT receptors."

Why Do Triptans Work? (Pharmacology Simplified)

"Triptans arrest nerve signaling in the nociceptive pathways of the trigeminovascular system, at least in the trigeminal nucleus caudalis and trigeminal sensory thalamus, in addition to promoting cranial vasoconstriction."

1. 5-HT1B activation (on blood vessel smooth muscle) → cranial vasoconstriction → reduces the dilated, inflamed meningeal vessels
2. 5-HT1D activation (on trigeminal nerve terminals - presynaptic) → blocks release of CGRP and Substance P → stops the neurogenic inflammation

The Complete Pathway: One Glance Summary

TRIGGERS (stress, sleep, hormones, food, light)
           ↓
HYPOTHALAMUS + BRAINSTEM over-activate
(prodrome: yawning, cravings, fatigue — hours before pain)
           ↓
CORTICAL SPREADING DEPRESSION  [in 25-30%]
(wave of depolarization, 2-4 mm/min, occipital → frontal)
           ↓  → AURA (zig-zag lights, numbness, dysphasia)
TRIGEMINOVASCULAR ACTIVATION
(trigeminal nerve fires → CGRP + Substance P + NO released)
           ↓
STERILE NEUROGENIC INFLAMMATION
(meningeal vessels dilate, plasma leaks, inflammation forms)
           ↓
PAIN SIGNALS → trigeminal nucleus caudalis → thalamus → cortex
= THROBBING HEADACHE (usually unilateral, 4-72 hours)
           ↓
CENTRAL SENSITIZATION
(allodynia, photophobia, phonophobia, osmophobia)
           ↓
POSTDROME (fatigue, brain fog, neck stiffness — the "hangover")

Summary Table — High-Yield for Exams

• Harrison's Principles of Internal Medicine, 22nd Edition (2025, McGraw-Hill) — Chapter 441
• Bradley and Daroff's Neurology in Clinical Practice — Chapter 102 (Pathophysiology section)
• Adams and Victor's Principles of Neurology, 12th Edition — Pathogenesis of Migraine
• Guyton and Hall Textbook of Medical Physiology — Chapter 49 (Headache)
• Goodman & Gilman's The Pharmacological Basis of Therapeutics — Chapter 5 (Serotonin and triptans)

• Right of Step 2: Genetics box (FHM mutations, family risk)
• Left of Step 3: Aura Types (visual, sensory, motor, speech)
• Right of Step 4: Why CGRP Matters + drug names (gepants, mAbs)
• Left of Step 6: Sensitization Cascade (1st → 2nd → 3rd order neurons)
• Right of Step 7: Why Triptans Work (5-HT1B + 5-HT1D explained simply)
• Left of Step 7: Neurotransmitters (CGRP, 5-HT, dopamine, NO, PACAP, glutamate)

• Small transition labels on each arrow shaft ("Brain enters alert state", "Electrical wave begins", etc.)
• Colour key legend
• Full source citations in the footer