By Dr. Drew Brennes, D.C. — The Nexus Letter Doctor
TL;DR — Quick Answer: In Nieves-Rodriguez v. Peake, 22 Vet. App. 295 (2008), the U.S. Court of Appeals for Veterans Claims held that the probative value of a medical opinion comes from its reasoning and rationale — not from the author's title or specialty. This means the VA cannot dismiss a properly reasoned nexus letter simply because a chiropractor, nurse practitioner, physician assistant, or non-specialist wrote it. What matters is not who signed the letter. What matters is how well the letter explains the connection.
In 2008, the United States Court of Appeals for Veterans Claims (CAVC) decided Nieves-Rodriguez v. Peake, 22 Vet. App. 295. The case involved a veteran whose claim rested in part on a private medical opinion. The Board of Veterans' Appeals had discounted that opinion. The CAVC stepped in to set the record straight on how medical opinions must be evaluated.
The ruling is now one of the most cited decisions in veterans' disability law. It is binding on every VA rater and every Board member. And most veterans have never heard of it.
The CAVC's holding was clear and specific. The probative value of a medical opinion — meaning its legal weight in the eyes of the VA — is not derived from the mere statement of a conclusion. It is derived from the reasoning and rationale that support it.
In other words, a doctor who simply writes "this veteran's condition is related to military service" has not produced a meaningful nexus opinion. The bare conclusion, standing alone, carries little to no weight. The VA may legally disregard it.
By contrast, a provider who explains why the connection exists — citing the veteran's specific records, describing the recognized medical mechanism, and grounding the opinion in peer-reviewed literature — has produced an opinion the VA must meaningfully weigh. The rater cannot dismiss it without explaining on the record why they rejected it.
The Court also made clear what a properly reasoned opinion must reflect:
Without that foundation, the opinion is legally deficient regardless of who wrote it.
Here is the part veterans most often get wrong. The Nieves-Rodriguez standard is about reasoning quality, not credential type. The ruling does not restrict nexus opinions to medical doctors. It does not require a specialist. It requires a qualified provider who produces a reasoned, record-based, literature-supported opinion.
Any licensed medical provider holding a valid National Provider Identifier (NPI) number can write a nexus letter. This includes:
The NPI number is the federal credential that identifies a licensed provider in the healthcare system. It is the practical marker the VA uses to recognize a provider as qualified. If a provider holds an active NPI and is licensed in their state, their opinion is eligible for VA consideration — full stop.
What disqualifies an opinion is not the provider's specialty. What disqualifies an opinion is the absence of reasoning. A one-sentence opinion from a board-certified neurosurgeon carries no more legal weight than a one-sentence opinion from a general practitioner, if neither provides a rationale. Conversely, a thoroughly reasoned opinion from a chiropractor or nurse practitioner must be given meaningful consideration.
Based on Nieves-Rodriguez and the body of CAVC case law that followed it, a valid nexus letter must contain several core elements. Each one is essential.
1. A confirmed current diagnosis. The condition being claimed must be formally documented with an ICD-10 code from a treating provider. A nexus opinion cannot connect a condition to service if the condition itself is not clinically established.
2. An identified in-service event, injury, or exposure. The letter must name what happened during military service. A vague reference to "service" is not enough. Specific occupational exposures, documented injuries, or patterns of activity must be identified.
3. A medical opinion using the correct legal threshold. The opinion must be stated as "at least as likely as not" — meaning a probability of 50 percent or greater. Language like "may be," "could be," or "possible" falls below this threshold. The VA reads that language literally. When it falls short, the claim falls with it.
4. A clinical rationale explaining the mechanism. This is the heart of the Nieves-Rodriguez standard. The examiner must explain, in pathophysiologic terms, why the in-service event produced or contributed to the current condition. This explanation must be specific to the veteran — not a generic medical statement.
5. Peer-reviewed medical literature. The examiner cites published, peer-reviewed studies that support the stated mechanism. This establishes that the opinion rests on accepted medical science, not personal belief. It is also what makes the opinion most difficult for a C&P examiner to dismiss.
6. A restatement of the final opinion. The conclusion ties the literature, the rationale, and the veteran's specific facts together into a clear final opinion that the adjudicator can follow from start to finish.
Remove any one of these elements and the letter weakens. Remove several and it becomes a bare conclusion — exactly what Nieves-Rodriguez says the VA may disregard.
One of the most common ways VA raters and C&P examiners improperly discount private nexus opinions is by citing the author's specialty. You may have seen language like this in a denial:
"The private opinion was provided by a chiropractor, whose scope of practice does not include the claimed condition."
"The private medical opinion was given less weight as the provider is not a specialist in this area."
Under Nieves-Rodriguez, that reasoning is legally deficient. The CAVC did not say that only specialists produce valid opinions. It said that valid opinions must contain reasoning. A rater who discounts a well-reasoned opinion from a non-specialist — without addressing the substance of that reasoning — is not applying the Nieves-Rodriguez standard correctly. That error is exactly the kind of legal error that gets Board decisions reversed on appeal.
This does not mean that specialty is irrelevant. A neurosurgeon's opinion on a brain injury claim may carry additional persuasive weight. An orthopedic surgeon's opinion on a complex intra-articular finding may be particularly compelling. But "additional persuasive weight" is different from "the only opinion that counts." The two are not interchangeable. And a well-reasoned opinion from a provider within their scope of training — even if not a specialist in the claimed condition — is entitled to meaningful consideration.
Nieves-Rodriguez did not emerge in a vacuum. Nearly a decade earlier, in Pond v. West, 12 Vet. App. 341 (1999), the CAVC had already established a foundational principle: the VA cannot automatically exclude a medical opinion based solely on the provider's credential type.
In that case, a chiropractor's nexus opinion was at issue. The Board had dismissed it on the basis that chiropractors are not qualified to render opinions on the claimed condition. The CAVC reversed. It held that a categorical exclusion of provider types is not the correct standard. The correct standard is to evaluate the quality and reasoning of the opinion itself.
Pond v. West opened the door. Nieves-Rodriguez defined what had to walk through it. Together, they establish a clear legal framework: any qualified, licensed provider can write a nexus opinion, and the VA must evaluate it on the merits of its reasoning — not on the letters after the author's name.
For the full story of Pond v. West and how a chiropractor-veteran's fight in 1999 changed veterans' law, see Pond v. West (1999): How a Chiropractor Started the Nexus Letter Revolution.
What does this mean for your claim?
First, you are not limited to your primary care physician. Any licensed provider within scope can write your nexus letter. If your VA primary care doctor won't write it, or writes a one-sentence note that doesn't contain rationale, you are not stuck. You can seek an independent nexus opinion from any qualified provider whose training covers your claimed condition.
Second, the quality of the letter matters more than the specialty of who wrote it. A thorough, record-reviewed, literature-supported opinion from a nurse practitioner or chiropractor will outperform a bare conclusion from a specialist. Under Nieves-Rodriguez, the reasoning is what the VA must weigh.
Third, if your claim was denied because the VA dismissed a private nexus opinion on credential grounds, that denial may be legally flawed. A supplemental claim or Higher-Level Review, supported by a new and properly reasoned nexus letter, is often the correct path forward. The error in the denial is itself part of your argument on appeal.
Fourth, the 2026 secondary causation update still applies. Effective May 1, 2026, the VA updated the secondary service connection causation framework following Spicer v. McDonough. Any nexus letter for a secondary claim — regardless of who writes it — must now use "but for" causation language under 38 CFR §3.310. See The VA Changed the Rules on Secondary Claims: What the New 'But For' Standard Means for Your Nexus Letter (2026) for the full breakdown.
It requires that a medical opinion contain reasoning and rationale — not just a conclusion. The examiner must show they reviewed the relevant records and literature, and applied both to the veteran's specific facts. A bare conclusion, without that foundation, is entitled to little or no weight.
Any licensed provider with an active NPI can write a nexus opinion within their scope of training and practice. Scope matters: a chiropractor is well within scope for musculoskeletal claims. A psychologist is within scope for mental health claims. A nurse practitioner is within scope for a wide range of primary care conditions. The provider should be honest about their scope and stick to what they can credibly support.
That is often an improper basis for denial under both Pond v. West and Nieves-Rodriguez. If the VA dismissed a properly reasoned opinion on credential grounds alone, that is a legal error. You should raise that error in your appeal or Higher-Level Review, supported by a new nexus letter that makes the Nieves-Rodriguez standard explicit on its face.
Yes — when the causal pathway runs through musculoskeletal or biomechanical mechanisms a chiropractor is trained to evaluate. For example, a service-connected orthopedic condition causing obesity driving sleep apnea is squarely within a chiropractor's scope. For conditions requiring specialist-level diagnostic interpretation (cardiac catheterization findings, complex neurological imaging), a specialist opinion adds additional weight — but the chiropractor's nexus opinion on the causal pathway remains valid.
Not necessarily — but a well-drafted letter is written in a way that satisfies the Nieves-Rodriguez standard on its face. It reviews the records, explains the mechanism, cites the peer-reviewed literature, and delivers a rationale-backed opinion at the correct legal threshold. The rater reading it should not need to be told what standard it meets — the letter should make that obvious.
Pond v. West (1999) addressed who can write a nexus opinion — it held that the VA cannot categorically exclude provider types like chiropractors. Nieves-Rodriguez (2008) addressed what a valid opinion must contain — it held that probative value comes from reasoning, not from a bare conclusion. Together, they cover the full picture: any qualified provider can write one, and it must contain a reasoned rationale to carry weight.
Think You Need a Nexus Letter?
I've written hundreds of nexus letters for veterans across the United States and internationally — each one built to satisfy the Nieves-Rodriguez standard on its face. If you have a diagnosis, an in-service event, and a medical connection worth documenting, I'd be glad to take a look at your case.
>> Request a Free Consultation at NexusLetterDoctor.com <<
Dr. Drew Brennes, D.C. is the founder of Nexus Letter Doctor. He specializes in writing medically and legally sufficient nexus letters for veterans pursuing VA disability claims, combining peer-reviewed medical literature with the specific evidentiary standards the VA is required to apply. For a consultation or to learn more, visit nexusletterdoctor.com.
This article is for informational purposes only and is not legal advice. It is intended to help veterans understand the court decisions that govern the evaluation of medical opinions in VA disability claims. Always work with an accredited representative, attorney, or qualified medical provider when building your claim file.
