Nexus Letter for Migraines Secondary to TBI: Evidence and Mechanism (2026)

Why Secondary Service Connection Applies

Secondary service connection allows a veteran to be compensated for a condition that has been caused or aggravated by an already service-connected disability. For veterans with service-connected TBI, the VA recognizes a number of conditions that can be claimed as secondary, including migraines, vestibular dysfunction, sleep disturbance, mood disorders, and cognitive impairment.

Migraines secondary to TBI is a particularly common claim because post-traumatic headache is one of the most well-documented consequences of head injury. The International Classification of Headache Disorders (ICHD-3) includes a specific diagnostic category for headache attributed to traumatic injury to the head, with subcategories for acute and persistent post-traumatic headache.

The Medical Mechanism: TBI to Migraine

The clinical literature recognizes several mechanisms by which TBI can produce or worsen migraine.

Direct Neurovascular Disruption

TBI — especially blast exposure and blunt trauma — can damage the trigeminovascular system, the network of nerves and blood vessels that play a central role in migraine generation. Disruption of this system can produce sensitization and a lower threshold for migraine attacks.

Cortical Spreading Depression

Cortical spreading depression — a wave of neuronal and glial depolarization across the cortex — is implicated in migraine aura and may be triggered or facilitated by traumatic brain injury. Veterans with prior migraine susceptibility may experience increased frequency or severity of attacks following a TBI event.

Inflammatory and Neuroendocrine Changes

TBI produces neuroinflammatory changes that can persist for months or years and contribute to ongoing headache. Disruption of hypothalamic-pituitary axis function following TBI also has downstream effects on pain processing.

Cervical and Musculoskeletal Contributors

TBI events frequently involve concurrent cervical spine injury, which can contribute to cervicogenic headache and exacerbate migraine through musculoskeletal triggers.

Sleep Disruption

Sleep disturbance is a common post-TBI symptom and is itself a well-known migraine trigger. Disrupted sleep architecture following TBI can produce a positive feedback loop in which sleep loss precipitates migraines and migraines further disrupt sleep.

Diagnosing Post-Traumatic Migraine

A clear diagnosis of migraine — typically by a neurologist, headache specialist, or qualified primary care physician — is foundational to the claim. Diagnostic criteria include the following.

Migraine Without Aura

Recurrent headache attacks lasting 4–72 hours, with at least two of: unilateral location, pulsating quality, moderate or severe intensity, aggravation by routine physical activity. During the headache, at least one of: nausea or vomiting, photophobia and phonophobia.

Migraine With Aura

Recurrent attacks of unilateral, fully reversible visual, sensory, or other central nervous system symptoms that develop gradually, are usually followed by headache and migraine-associated symptoms.

Chronic Migraine

Headache occurring on 15 or more days per month for more than three months, which on at least eight days per month has the features of migraine headache.

Headache Attributed to Traumatic Injury to the Head (Post-Traumatic Headache)

Headache developing in close temporal relation to a traumatic injury to the head and lasting longer than three months (persistent) or less (acute). The headache may have migraine, tension-type, or mixed features.

Rating Migraines Under DC 8100

Migraines are rated under 38 CFR 4.124a, Diagnostic Code 8100, based on the frequency and severity of prostrating attacks.

50 Percent

With very frequent completely prostrating and prolonged attacks productive of severe economic inadaptability. This is the maximum rating under DC 8100. The "severe economic inadaptability" language refers to substantial interference with employment, not necessarily the inability to work entirely.

30 Percent

With characteristic prostrating attacks occurring on average once a month over the last several months.

10 Percent

With characteristic prostrating attacks averaging one in two months over the last several months.

0 Percent

With less frequent attacks. A 0 percent rating reflects that the condition is service-connected but does not meet the criteria for a compensable rating at the time of evaluation. This rating may later be increased if the condition worsens.

What "Prostrating" Means

The term "prostrating" is central to the DC 8100 analysis. The VA does not have a single regulatory definition, but the Court of Appeals for Veterans Claims and the Board of Veterans' Appeals have generally interpreted prostrating to mean attacks that cause the veteran to stop ordinary activity, lie down, and seek a quiet, dark environment until the attack resolves.

Attacks may be considered prostrating without requiring an emergency room visit. Headache diaries documenting attack frequency, duration, severity, accompanying symptoms (nausea, vomiting, photophobia, phonophobia), and functional impact during the attack are valuable evidence. A medical opinion characterizing typical attack severity is also helpful.

Evidence for a Migraines-Secondary-to-TBI Claim

A defensible claim typically rests on the following evidence.

Service Connection for the Underlying TBI

The TBI must already be service-connected — or being claimed concurrently. Documentation of the in-service mechanism (blast exposure, vehicle accident, fall, training injury), Line of Duty paperwork if available, and post-TBI medical records support the foundation.

Onset of Headache Pattern

Records establishing when the migraine pattern began — ideally documenting onset within a clinically reasonable timeframe after the TBI — are important. Veterans whose migraines began shortly after the TBI event have a clear temporal relationship; those whose migraines emerged later may need a stronger medical rationale articulating delayed-onset post-traumatic headache or aggravation of pre-existing migraine.

Neurology Evaluation

Evaluation by a neurologist or headache specialist who has characterized the headache type, ruled out other causes, and articulated the relationship to the TBI strengthens the record.

Headache Diary

A daily or weekly diary recording attack frequency, duration, severity (typically on a 0–10 scale), accompanying symptoms, triggers, and functional impact provides concrete evidence supporting the prostrating-attack analysis under DC 8100.

Treatment Records

Records of acute and preventive medication trials (triptans, NSAIDs, beta-blockers, anti-epileptics, CGRP antagonists, Botox), responses to treatment, and emergency department visits when applicable.

Lay Statements

Statements from family members or coworkers describing the impact of attacks on daily life and work.

Nexus Opinion

A licensed physician's opinion articulating that the migraines are at least as likely as not caused or aggravated by the service-connected TBI, with rationale referencing the relevant clinical literature and the veteran's specific record.

Elements of a Strong Nexus Letter

A strong nexus letter for migraines secondary to TBI contains the following elements.

Identification of the Service-Connected TBI

The letter should reference the existing TBI service connection, the in-service mechanism, and the relevant medical records.

Current Migraine Diagnosis

The letter should identify the migraine diagnosis specifically (migraine with or without aura, chronic migraine, post-traumatic headache) and reference the records supporting the diagnosis.

Medical Mechanism

The letter should articulate the medical mechanism — neurovascular disruption, trigeminovascular sensitization, neuroinflammatory changes, cervical contribution, sleep mediation — connecting the TBI to the migraine pattern, supported by reference to the relevant literature.

Causation or Aggravation

The opinion should specify whether the TBI caused the migraine de novo or aggravated a pre-existing migraine condition. If aggravation, the letter should articulate the baseline severity and the worsening attributable to the TBI.

"At Least as Likely as Not" Language

The opinion must use the VA's required threshold — that the migraine condition is at least as likely as not (50 percent or greater probability) caused or aggravated by the service-connected TBI.

Records Review

The letter should affirm that the physician reviewed the service treatment records, post-service medical records, neurology evaluations, and any imaging or test results before forming the opinion.

Aggravation of Pre-Existing Migraines

Some veterans had migraines before service or before the in-service TBI event. In those cases, secondary service connection can be established on an aggravation theory rather than direct causation. The nexus letter should address:

• The baseline migraine pattern before the TBI (frequency, severity, functional impact).
• The change in pattern after the TBI (increased frequency, increased severity, new features such as aura, refractoriness to prior treatments).
• The medical reasoning for why the worsening exceeds the natural progression of the underlying migraine condition.

Aggravation claims are evaluated based on the increment of worsening attributable to the service-connected condition. The VA assigns a separately calculated aggravation rating reflecting that increment.