Anatomy of a Strong VA Nexus Letter

This is an educational reference showing what a thorough nexus letter typically contains and why each section matters. It is not a fillable template, and it is not a substitute for a medical opinion from a clinician who has reviewed your specific record. The fictional veteran, condition, and clinician below are illustrative only.

Not a fillable template. A nexus letter is a medical opinion. It must be authored by a clinician who has reviewed the veteran's actual records and reached an independent conclusion. Submitting a generic or template letter without clinician-specific analysis carries little weight and may hurt the claim.

Annotated Example (Fictional)

Letterhead. Provider's name, credentials, practice address, license number, and contact information. Establishes the writer's qualifications at first glance.
Letterhead JANE M. CARTER, MD Board-Certified, Internal Medicine License #IL-MD-12345 Carter Medical Group, 100 Main Street, Springfield, IL 60601 (555) 123-4567 | jcarter@cartermedical.example.com Date and Recipient May 1, 2026 Department of Veterans Affairs Regional Office, [city] RE: [Veteran name], SSN xxx-xx-1234 Claim: Service Connection for Obstructive Sleep Apnea Secondary to Service-Connected PTSD Records Reviewed In preparing this opinion I have reviewed the following: - Veteran's full VA C-file, dated November 2024 - Service Treatment Records (1998-2002) - VA medical records, 2003-2025 - Private treatment records from Springfield Pulmonary Associates, 2019-2025 - Sleep study (polysomnography) report, dated June 12, 2023 - Lay statements from veteran's spouse, dated August 2024 - Peer-reviewed medical literature cited at the end of this letter Veteran's Relevant History The veteran served on active duty in the U.S. Army from 1998 to 2002, including combat deployment to Iraq in 2003 (post-discharge involuntary recall). He is service-connected at 70% for PTSD (effective 2010). His PTSD treatment record reflects chronic hyperarousal, frequent nightmares, and prescribed prazosin and sertraline since 2012. He was diagnosed with moderate-to-severe obstructive sleep apnea (AHI 32) on June 12, 2023, and currently uses CPAP therapy with documented compliance. Medical Reasoning The veteran's obstructive sleep apnea was first diagnosed in 2023, well after his PTSD onset and treatment. The clinical picture, severity of PTSD with sleep-fragmenting hyperarousal, long-term use of sertraline (a sedating SSRI with known weight-gain effects), and absence of predisposing factors before military service, supports a causation theory under the published literature on PTSD-OSA comorbidity (see, e.g., Colvonen et al., Sleep Medicine Reviews, 2018; Mysliwiec et al., Chest, 2019). Body habitus changes during PTSD treatment, combined with upper-airway tone changes attributable to autonomic dysregulation, explain the development of OSA in a veteran with no pre-service or in-service risk factors. I have considered alternative causes (age, family history of OSA, alcohol use). The veteran reports no family history, modest alcohol use within guidelines, and his BMI increase post-2012 is directly attributable to documented sertraline weight gain. These factors are insufficient to explain the OSA in isolation. Opinion Statement It is my opinion that it is at least as likely as not (50 percent or greater probability) that [Veteran name]'s obstructive sleep apnea was caused or aggravated by his service-connected post-traumatic stress disorder. Rationale Summary This opinion is based on: (1) the temporal sequence (PTSD predates OSA diagnosis by over a decade), (2) the established medical literature on PTSD-OSA comorbidity, (3) the documented weight gain attributable to PTSD pharmacotherapy, and (4) the absence of alternative pre-service or non-service risk factors sufficient to explain the OSA independently. Signature Sincerely, [Signature] Jane M. Carter, MD Board-Certified, Internal Medicine [Date] Literature Cited 1. Colvonen PJ et al. "Obstructive sleep apnea and posttraumatic stress disorder among OEF/OIF/OND veterans." Sleep Medicine Reviews. 2018. 2. Mysliwiec V et al. "Sleep Disorders in US Military Personnel: A High Rate of Comorbid Insomnia and Obstructive Sleep Apnea." Chest. 2019.

Why Each Section Matters

  • Letterhead. Establishes credentials before the substance is read. Adjudicators weigh specialist opinions more heavily, and a license number lets VA verify the writer is who they claim.
  • Records reviewed. An opinion without a stated record review is treated as speculative. Listing the documents reviewed defeats the "no foundation" critique VA often applies to bare opinions.
  • Veteran's relevant history. Demonstrates the clinician understands the specific claim, not a generic template. Anchors the opinion to the actual record.
  • Medical reasoning. The single most important section. A bare conclusion ("PTSD causes OSA") carries little weight. A reasoned explanation citing literature carries substantial weight.
  • Opinion statement. The "at least as likely as not" formulation is the legal standard. Softer language ("possible," "may be related") falls below the 50-percent probability bar and is regularly discounted.
  • Rationale summary. Restates the four-or-five factors driving the conclusion. Gives the adjudicator a clean paragraph to quote in the rating decision.
  • Literature cited. Optional but powerful. Peer-reviewed sources counter the "this is the clinician's hunch" critique.

The Aggravation Variant

For aggravation claims under 38 CFR 3.310(b), the opinion needs one additional element: a stated baseline severity. The opinion identifies how severe the secondary condition was before the aggravating service-connected condition appeared or worsened, and how much worse it is now. Without that baseline, VA cannot compute the rateable increase.

Example wording from the literature: "Prior to the documented worsening of the veteran's service-connected lumbar spine condition in 2020, his pre-existing depression was characterized by mild symptoms managed with one antidepressant. Since 2020, the depression has progressed to moderate severity requiring two medications and weekly therapy. In my opinion, the additional disability above the prior baseline is at least as likely as not aggravated by the worsened spine condition."

Educational reference only, not legal or medical advice. For help with your claim, find an accredited VSO representative.