For many veterans, the hardest VA disability claims to win are secondary claims not because the conditions aren’t real, but because the VA requires precise medical proof connecting one disability to another.
Here’s the reality:
Without strong medical nexus evidence, most secondary VA claims fail.
That’s why a Nexus Letter for a secondary condition is often mission-critical.
In this comprehensive guide, VA disability expert Brian Reese explains what a Nexus Letter is, how secondary service connection works, the legal standard the VA applies, and provides two high-quality sample Nexus Letters veterans can use as templates when working with a medical provider.
“A Nexus Letter is often the difference between approval and denial,” Reese explains.
“The VA doesn’t guess. You must connect the dots for them medically and legally.”Also Read
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What Is a Nexus Letter for VA Disability Benefits?
A Nexus Letter is an evidence-based medical opinion written by a qualified healthcare provider. Its purpose is to establish a clear link (“nexus”) between:
- A current disability and
- Military service or
- An already service-connected disability (secondary service connection)
A Nexus Letter is considered an independent medical opinion, and when done correctly, it carries significant probative value with VA raters.
“Not all Nexus Letters are equal,” notes a VA-accredited claims consultant.
“Quality, reasoning, and provider credibility determine whether the VA takes it seriously.”
What Is VA Secondary Service Connection?
Secondary service connection applies when a new disability is:
- Proximately due to
- Caused by, or
- Aggravated by
an existing service-connected condition rated at 0% or higher.
Simple Example
A veteran is service-connected for a knee injury. Over time, that knee injury causes an altered gait, leading to chronic lower back pain. The lower back condition can be claimed secondary to the knee.
“Secondary claims are about cause-and-effect over time,” Reese explains.
“They reflect how one injury leads to another in real life.”
Legal Standard: 38 CFR § 3.310 (Secondary Service Connection)
Under federal regulation, the VA may grant service connection when:
Secondary Causation
A new disability is directly caused by a service-connected condition.
Secondary Aggravation
A non-service-connected condition is permanently worsened beyond natural progression by a service-connected disability.
“Aggravation claims are often overlooked, but they are just as valid under VA law,” says a veterans’ law attorney.
How to Establish Secondary Service Connection (3 Required Elements)?
1. A Current Medical Diagnosis
You must have a documented diagnosis of the secondary condition. A diagnosis within the last 12 months is strongly recommended.
2. A Primary Service-Connected Disability
The primary condition must already be service-connected at 0% or higher.
3. Medical Nexus Evidence
This is where most claims fail.
A Nexus Letter must state that the secondary condition is:
“At least as likely as not (50% probability or greater)”
caused or aggravated by the primary service-connected condition.
“Without a nexus opinion, the VA has no legal basis to grant a secondary claim,” Reese emphasizes.
Why a Strong Nexus Letter Matters?
A well-written Nexus Letter:
- Explains why the conditions are connected
- Cites medical reasoning and clinical findings
- Uses correct VA legal language
- Addresses causation or aggravation
“The VA doesn’t deny secondary claims because they disagree medically,” notes a VA rater.
“They deny them because the evidence isn’t clearly written.”
Overview: What Makes a Strong Nexus Letter
| Element | Why It Matters |
|---|---|
| Qualified medical provider | Establishes credibility |
| Review of records | Shows informed opinion |
| Clear diagnosis | Confirms disability |
| Medical rationale | Explains causation |
| VA legal language | Meets VA standard |
| Signed & dated | Required for validity |
Sample Nexus Letter 1: Sleep Apnea Secondary to PTSD
[Veteran’s Full Name]
[SSN / VA Claim Number]
[Date]
To Whom It May Concern:
I, Dr. [Doctor’s Full Name], am a licensed medical professional specializing in [Specialty]. I have reviewed the medical records and examined [Veteran’s Name]. It is my professional opinion that it is at least as likely as not (50% probability or greater) that the veteran’s Obstructive Sleep Apnea (OSA) is secondary to or aggravated by their service-connected Post-Traumatic Stress Disorder (PTSD).
Medical Background
The veteran has a confirmed diagnosis of PTSD and has experienced chronic symptoms including nightmares, hypervigilance, anxiety, and sleep disturbance. The veteran has also been diagnosed with OSA confirmed by sleep study.
Medical Rationale
Medical research supports a strong association between PTSD and sleep-disordered breathing. PTSD-related hyperarousal, fragmented sleep, and increased sympathetic nervous system activity contribute to airway instability and worsened apnea events.
Nexus Opinion
Based on medical history, examination findings, and accepted medical literature, it is at least as likely as not that the veteran’s OSA is caused or aggravated by PTSD.
Sincerely,
[Doctor’s Signature & Credentials]
“Sleep apnea secondary to PTSD is one of the most frequently approved secondary claims when the nexus is written correctly,” Reese notes.
Sample Nexus Letter 2: Lower Back Condition Secondary to Knee Disability
[Veteran’s Full Name]
[SSN / VA Claim Number]
[Date]
To Whom It May Concern:
I, Dr. [Doctor’s Full Name], specialize in [Orthopedics/Physical Medicine]. After reviewing the veteran’s records and examination, it is my opinion that it is at least as likely as not that the veteran’s lower back condition is secondary to their service-connected knee condition.
Medical Background
The veteran’s knee condition causes chronic pain and instability, resulting in altered gait mechanics over time.
Medical Rationale
Medical literature consistently shows that abnormal gait patterns increase mechanical stress on the lumbar spine, accelerating degenerative changes and chronic pain.
Nexus Opinion
It is at least as likely as not that the veteran’s lumbar condition is caused or aggravated by the service-connected knee disability.
Sincerely,
[Doctor’s Signature & Credentials]
“Biomechanical secondary claims like this are some of the strongest when properly documented,” explains a VA orthopedic consultant.
Common Reasons Nexus Letters Fail
- No medical reasoning
- Wrong legal standard used
- Provider lacks credentials
- Vague language
- No record review
“A weak Nexus Letter can actually hurt a claim,” Reese warns.
Do You Really Need a Nexus Letter for a Secondary Claim?
Legally? Not always.
Practically? Almost always.
“If you’re filing secondary without a Nexus Letter, you’re gambling,” Reese says.
“And the odds are not in your favor.”
Why Veterans Struggle to Get Quality Nexus Letters?
- Private doctors unfamiliar with VA standards
- High costs ($1,500–$2,000 is common)
- Incomplete or poorly written opinions
“Doctors know medicine but not VA law,” notes a veteran advocate.
“That gap is where most claims break down.”
Final Thought
Secondary VA disability claims are winnable but only when the evidence is built correctly. A high-quality Nexus Letter is often the missing piece that transforms a denial into an approval.
“If the VA can’t clearly see the connection, they won’t assume it,” Reese concludes.
“Your Nexus Letter must do the heavy lifting.”
FAQs
Is a Nexus Letter required for a secondary VA claim?
Not legally, but in most cases it’s essential to get approved.
Who can write a Nexus Letter?
A licensed medical professional with expertise related to your condition.
Does the Nexus Letter need to be from a VA doctor?
No. Private medical opinions are valid and often very effective.
What wording must a Nexus Letter include?
“At least as likely as not (50% probability or greater).”
Can a Nexus Letter prove aggravation, not just causation?
Yes. It can support claims where a service-connected condition made another condition worse.
How long should a Nexus Letter be?
Usually 1–3 pages clear and medically detailed.
