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Nexus letter guide · 8100

Nexus Letter for Migraines: What It Must Say

The medical opinion connecting Migraines (8100) to your service is the piece of the file a rater weighs most heavily. This is what that letter has to contain — and a complete, real example you can read before writing a word.

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The published example letter — an invented veteran and a fictional sample provider.

Key facts

Rated under
38 CFR § 4.124a, DC 8100
Diagnostic code
8100
The standard
“At least as likely as not” — 50% or greater
Connection theories
Direct (§ 3.303) or secondary (§ 3.310) · 1 pathway below

The short answer

A migraine nexus letter is a medical opinion that your migraines are "at least as likely as not" caused by your service, or by a service-connected condition such as a traumatic brain injury, PTSD, or a neck injury. It needs a migraine diagnosis (not just "headaches"), a record of when the headaches started or got worse, and a mechanism tied to your file. The nexus letter decides service connection; the rating under DC 8100 depends on how often you have prostrating attacks, so a headache log matters as much as the letter.

What a nexus letter is

A nexus letter is a written medical opinion from a licensed clinician stating that a veteran’s condition is “at least as likely as not” (a 50 percent or greater probability) connected to their military service — or to a condition already service-connected. It is the bridge between a diagnosis and service connection: the VA has your diagnosis and your service records, and the nexus opinion is what ties them together with medical reasoning a rater can weigh.

The standard · 38 CFR § 3.102

“At least as likely as not”

The opinion does not have to be certain, or even “more likely than not.” A 50 percent or greater probability meets the standard; when the evidence is in approximate balance, the benefit of the doubt goes to the veteran.

What a Migraines nexus letter must contain

  1. 1

    The diagnosis, by name and code

    Migraines named as a current, documented diagnosis — the condition the VA rates under 38 CFR § 4.124a, DC 8100 (8100). No diagnosis, no service connection: the opinion has to be about a condition that exists in your records.

  2. 2

    The theory of connection

    Direct service connection under 38 C.F.R. § 3.303 (the condition began in or was caused by service), or secondary service connection under § 3.310 (a service-connected condition caused or aggravated it). For Migraines, the secondary path is common — see the mechanisms below — and the letter must name which theory it is using.

  3. 3

    The magic words, used correctly

    The opinion must be stated to the VA's own standard: "at least as likely as not (a 50 percent or greater probability)." Weaker hedges like "possibly" or "may be related" fail; the standard is a specific legal threshold, and letters that don't invoke it get discounted.

  4. 4

    A rationale, not a conclusion

    The most common fatal flaw is the conclusory letter — an opinion with no reasoning. A rater is instructed to weigh the rationale: what in the records supports the connection, what the medical literature says about the mechanism, and why known alternative causes don't displace it. For Migraines specifically: Headache log with dates, duration, and prostrating episodes documented.

  5. 5

    A licensed clinician's signature and credentials

    The letter is medical evidence only when a licensed clinician — opining within their specialty — reviews it, exercises independent judgment, and signs it with their credentials. VA Claim Commander drafts the letter from your records and your story; your clinician signs it. An unsigned draft is a draft.

What a rater looks for in a Migraines nexus letter

  • Migraine, diagnosed

    Migraine named by a neurologist or your primary care provider, with the features that make it migraine: one-sided throbbing pain, nausea, sensitivity to light or sound, aura. "Headaches" in a problem list is weaker evidence.

  • Onset tied to service

    Headaches at sick call, after a blast or head injury, or starting during a deployment. If they began after discharge, the letter needs a service-connected cause instead.

  • A mechanism for a secondary claim

    Post-traumatic headache after a TBI, stress and poor sleep lowering the migraine threshold in PTSD, or pain referred from a service-connected neck condition. The letter should say which and point to where your records show it.

  • Other causes addressed

    Medication overuse, sleep apnea, a post-service head injury, and family history of migraine. A strong letter names the ones in your file and explains why the service-connected cause still accounts for the headaches.

  • No double counting with TBI

    If you have a service-connected TBI, headaches may already be part of that rating. A distinct migraine diagnosis can be rated separately under DC 8100, but the same symptom cannot be rated twice (38 C.F.R. § 4.14), so the letter should be clear about the diagnosis.

Direct service connection for Migraines

Direct service connection under 38 C.F.R. § 3.303 means the migraines began in service. Common anchors:

  • Headaches in service treatment records

    Sick-call visits, medication for headaches, or a neurology referral while you were in.

  • A blast, fall, or head strike

    Even without a TBI diagnosis, a documented head injury followed by headaches gives the clinician an event to connect.

  • People who saw it

    Fellow service members who saw you stop work, lie down in the dark, or get sick with headaches can describe it (38 C.F.R. § 3.159(a)(2)).

Example migraines nexus letter wording

The opinion section of a migraine nexus letter on a direct theory, for an invented veteran. A real letter is written by the clinician about your records.

Sample — Illustrative Specimen

Invented veteran · not a real medical opinion · do not copy as your own

Opinion: It is my medical opinion that the veteran's migraine without aura is at least as likely as not (a 50 percent or greater probability) related to his active service, beginning after the blast exposure documented in 2012.

Records reviewed: service treatment records, including the 2012 note after an improvised explosive device detonated near his vehicle and three later sick-call visits for headaches treated with sumatriptan; VA neurology records 2016 to 2026; and the veteran's headache log for the past six months.

History: The veteran reports no headaches before 2012. Since then he has had one-sided throbbing headaches with nausea and light sensitivity, and during attacks he stops what he is doing and lies down in a dark room. His log records one to two such attacks a month.

Rationale: Headaches that begin after a blast or head injury and take on migraine features are well described, and the record shows the headaches starting in service and treated continuously since. I considered family history and medication overuse: there is no family history of migraine recorded, and his use of abortive medication is within recommended limits. I considered his service-connected PTSD as a separate contributor; it may worsen the attacks, but the onset follows the blast exposure.

Filing Migraines as a secondary condition

Under 38 C.F.R. § 3.310, if a service-connected condition caused or aggravated Migraines, it is service-connected too. The nexus letter’s job becomes explaining the medical mechanism. The pathways veterans most commonly file:

PTSD / Mental HealthMigraines

Migraines secondary to PTSD / Mental Health

Chronic stress and neurological sensitization from PTSD lower the migraine threshold, increasing frequency and severity of headache episodes.

What proves it: Neurology or primary care headache records; migraine diary; nexus letter relating stress-induced cortical spreading to PTSD.

Full guide: Migraines secondary to PTSD / Mental Health

Conditions often claimed secondary to Migraines

Once Migraines is service-connected, conditions it causes or makes worse can be claimed under 38 C.F.R. § 3.310. Each one needs its own nexus opinion explaining that link.

Why nexus letters fail

  • Conclusory: an opinion with no rationale. The rater is told to weigh reasoning, and a bare “it’s related” weighs nothing.
  • Wrong standard: “may be related” or “possibly caused by” instead of “at least as likely as not.”
  • Ignores the other causes: a strong letter names the recognized non-service risk factors and explains why they don’t displace the service connection.
  • Outside the specialty: a clinician opining far from their field gets less weight than one whose practice covers the condition.
  • Unsigned: a draft nobody signed is not medical evidence — it is homework.

Who can write a Migraines nexus letter

Any licensed clinician qualified to give a medical opinion on Migraines: a physician, or another licensed clinician opining within their field. VA's test is whether the person is qualified by education, training, or experience (38 C.F.R. § 3.159(a)(1)). It does not have to be a VA doctor. Your own treating provider, who already knows your history, is often the strongest choice.

VA Claim Commander drafts the letter from your records and your own words, so your clinician starts from a complete draft; they review it, change what they disagree with, and sign only if it is their opinion.

If your own doctor won't write one, a licensed clinician through Commander Health can review your records and, only if the evidence supports it, write and sign a nexus letter for Migraines. It is a flat $500 that includes the records review, separate from any VA Claim Commander plan, and the clinician can decline if your records don't support an opinion.

Ask your own doctor: draft the request Commander Health nexus letter

Common questions

Do I need a nexus letter for a Migraines VA claim?

If service connection isn't already established for Migraines, a medical nexus opinion is usually the piece a rater weighs most heavily. It connects the diagnosis (8100) to your service — or to an already service-connected condition — using the "at least as likely as not" standard. Presumptive claims are the main exception.

What must a nexus letter for Migraines say?

Four things: the current diagnosis by name and diagnostic code; the connection theory (direct under 38 C.F.R. § 3.303, or secondary under § 3.310); the opinion stated to the "at least as likely as not (50 percent or greater probability)" standard; and a medical rationale grounded in your records and the medical literature — not a bare conclusion. It must be signed by a licensed clinician.

Who has to sign a nexus letter?

A licensed medical professional — a physician, or another clinician opining within their specialty (38 C.F.R. § 3.159(a)(1) asks for someone qualified by education, training, or experience). VA Claim Commander drafts the letter from your own records and story; a licensed clinician reviews, exercises independent judgment, and signs. An unsigned draft is not medical evidence. If your own doctor won't write one, a licensed clinician through Commander Health can review your records and, only if the evidence supports it, write and sign a nexus letter for Migraines. It is a flat $500 that includes the records review, separate from any VA Claim Commander plan, and the clinician can decline if your records don't support an opinion.

Can Migraines be claimed secondary to another condition?

Yes — veterans commonly file Migraines secondary to PTSD / Mental Health under 38 C.F.R. § 3.310. In a secondary claim, the nexus letter's job changes: instead of connecting Migraines to service directly, it explains the medical mechanism by which the service-connected condition caused or aggravated it.

What does prostrating mean for a VA migraine rating?

The regulation does not define it. In practice it means an attack that stops you and makes you lie down, usually in a dark, quiet room. A headache log that records what each attack made you stop is better evidence than a pain score.

How does VA rate migraines?

Under 38 C.F.R. § 4.124a, DC 8100: 0% for less frequent attacks; 10% for prostrating attacks averaging one in two months over the last several months; 30% for prostrating attacks averaging once a month; and 50% for very frequent completely prostrating and prolonged attacks productive of severe economic inadaptability.

Can migraines be secondary to a TBI?

Yes, headaches after a traumatic brain injury are a common secondary claim under 38 C.F.R. § 3.310. When they meet the migraine diagnosis they can be rated under DC 8100, as long as the same symptoms are not also counted in the TBI rating.

Does severe economic inadaptability mean I can't work?

No. It is about the economic effect of the attacks, such as missed shifts, leaving work early, lost pay, or accommodations. Records of that impact help the 50 percent level.

How the VA rates Migraines →Migraines research library →Migraines (DC 8100): prostrating attacks →Migraines secondary to PTSD →VA disability calculator →

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