Diagnosis and Red Flags: Is It 'Just' a Migraine?

While migraine without aura is a biological condition, there is no blood test or brain scan that can diagnose it. Instead, doctors use a gold-standard set of rules called the ICHD-3 (International Classification of Headache Disorders, 3rd edition) ^[1]. Diagnosis is a process of matching your symptoms to these criteria while simultaneously watching for “red flags” that might suggest your head pain is caused by another underlying condition—known as a secondary headache ^[2][3].

The Rules for Diagnosis: ICHD-3

To be diagnosed with migraine without aura, your experience must follow a specific pattern over time. A single bad headache is rarely enough for a firm diagnosis. According to the ICHD-3, you must have had at least five attacks that meet the following criteria ^[2][4]:

1. Duration: Each attack lasts between 4 and 72 hours (when untreated or unsuccessfully treated) ^[2].
2. Pain Characteristics: The headache must have at least two of these four features ^[2]:
   • Located on only one side of the head (unilateral).
   • A pulsating or throbbing quality.
   • Moderate or severe pain intensity.
   • Aggravation by (or causing avoidance of) routine physical activity, such as walking or climbing stairs.
3. Associated Symptoms: During the headache, you must have at least one of the following ^[2]:
   • Nausea and/or vomiting.
   • Sensitivity to both light (photophobia) and sound (phonophobia).
4. No Better Fit: The symptoms cannot be better explained by another ICHD-3 diagnosis ^[2].

If you meet some but not all of these (for example, you have all the features but have only had three attacks), a doctor may give a diagnosis of probable migraine ^[5]. This is a clinician’s classification while evaluating your pattern, not an automatic label.

Distinguishing Migraine from Other Headaches

Migraine is often confused with other primary headache disorders. Your doctor will look for key “discriminators” to tell them apart:

• Tension-Type Headache: These are typically felt on both sides of the head, feel like a steady “band” or pressing (not pulsating), and often lack the nausea seen in migraine. While they can include mild photophobia or phonophobia, they do not usually have both ^[6][7].
• Cluster Headache: This is much rarer and involves strictly one-sided, excruciating pain, often centered around the eye ^[8]. Unlike the desire to lie still in a dark room with a migraine, people with cluster headaches are often restless and may pace the room ^[9]. They also experience “autonomic” symptoms on the same side as the pain, such as a red/tearing eye or a stuffy nose ^[10].

Red Flags: When to Seek Urgent Care

While migraine is a “primary” headache (the disease itself), a “secondary” headache is a symptom of another medical problem. Doctors use the SNNOOP10 checklist (an acronym for screening secondary causes) to look for these more serious conditions ^[3][11]. Please be aware that a known migraine diagnosis does not make a changed headache automatically safe.

🚨 EMERGENCY: Call 911 or go to an emergency department immediately if you experience:

• A thunderclap headache that reaches its maximum, “worst ever” intensity within one minute ^[12].
• New focal weakness, numbness, confusion, seizures, or difficulty speaking or seeing, even if the symptom resolves ^[13].
• A severe headache accompanied by a fever and a stiff neck or an unexplained rash.
• A new, severe headache during pregnancy or the postpartum period ^[14].
• A painful red eye with visual changes ^[10].

⚠️ PROMPT CARE: Schedule an urgent outpatient visit if you experience:

• S (Systemic symptoms/Secondary risk): A new headache if you have a history of cancer, an impaired immune system, or recent head trauma ^[3].
• O (Older age): A new or different headache pattern starting after age 50 ^[15].
• P (Pattern change): A headache that is fundamentally different from your usual attacks or is progressively getting worse.
• P (Positional): Pain that significantly changes when you go from lying down to standing up, or vice versa ^[16].
• P (Precipitated by exertion): Pain triggered strictly by coughing, sneezing, or physical straining ^[17].

The Role of Brain Scans (MRI and CT)

A common misunderstanding is that everyone with a migraine needs a brain scan. In reality, medical guidelines from the American Headache Society (AHS) advise against routine neuroimaging (like MRI or CT) for patients whose headaches fit a stable, stereotyped (looks the same every time) migraine pattern and who have a normal neurologic and funduscopic (eye) exam ^[18][19].

• When imaging is NOT needed: If your attacks are stereotyped, have occurred for years, and your doctor finds no issues during a physical exam, a scan is unlikely to show any abnormality that would change your treatment ^[18][20].
• When imaging IS needed: Scans are used for atypical presentations, the “first or worst” headache of your life, or when one of the red flags listed above is present ^[18][21]. In emergencies like a thunderclap headache, a CT is often used first; an MRI is often preferred for nonurgent atypical patterns ^[22][23].

Seeking an MRI purely for “reassurance” is a personal decision that should be individualized. Be aware that scans often find incidentalomas—small, harmless variations in brain structure that are not related to your pain but can sometimes require stressful follow-up ^[24].

When to follow up: Describe migraine as a recurrent condition with a variable course. Reassess with your clinician when your attacks change, during preventive trials, or if your disability or mood worsens.