Do You Need a Nexus Letter for Secondary Conditions?

Secondary conditions are one of the most confusing parts of the VA disability process. The standards for proving them are inconsistent, and veterans get denied all the time even when the medical connection seems obvious.

You submit evidence, explain your symptoms, and still end up wondering why the VA did not recognize the link.

Nexus letters for secondary conditions are often the missing piece that shows the VA how a service-connected disability caused or aggravated another condition.

While not all secondary claims require a nexus letter, a strong one can be the difference between approval and denial.

This guide explains when you need a nexus letter for a secondary condition, which conditions typically require one, and includes a sample letter to help you strengthen your claim and get approved.

What is a Secondary Service Connection?

A secondary service connection basically means the VA has already recognized one condition as service-related, and that condition causes another issue or makes your intial condition worse.

There are two types of secondary service connections:

1. Secondary Causation: The new condition was directly caused by the service-connected one.

   Example: Veteran has PTSD that causes sleep apnea.

2. Secondary Aggravation: A non-service-connected condition gets worse because of the service-connected one.

   Example: Veteran has pre-existing PTSD which worsened after service.

To qualify for a secondary service connection, you need a VA-rated primary condition first. It also helps if your secondary condition develops after your primary condition.

Examples of Secondary Connections

While this list does not cover every single secondary condition, here are the most common ones veterans file claims for and how the two conditions are related.

• PTSD → Sleep Apnea: PTSD and Sleep apnea can be related because PTSD can disrupt normal sleep patterns and contribute to airway relaxation or weight gain that worsens sleep apnea.

• Hypertension → Sleep Apnea: Elevated blood pressure can stiffen and narrow blood vessels, reducing oxygen flow and predisposing veterans to airway obstruction during sleep.

• Tinnitus → Sleep Apnea: Constant ringing and sleep disturbance from tinnitus can lead to poor sleep hygiene and weight gain, increasing the risk of obstructive sleep apnea. A nexus letter for sleep apnea secondary to tinnitus is must provide tons of medical literature because it is way harder to prove.

• Depression → Sleep Apnea: Fatigue, inactivity, and medication side effects tied to depression can cause weight gain and airway muscle relaxation that trigger sleep apnea.

• PTSD → Hypertension: The prolonged stress response and heightened adrenaline associated with PTSD often keep blood pressure chronically elevated, resulting in hypertension.

• Rhinitis → Sleep Apnea: Chronic nasal congestion from rhinitis obstructs airflow, forcing mouth breathing and increasing the likelihood of sleep apnea episodes.

• GERD → Sleep Apnea: Acid reflux inflames the upper airway and can cause nighttime choking or coughing, worsening sleep apnea symptoms.

• Traumatic Brain Injury → Chronic Migraine: Damage from TBI can alter brain pain pathways and vascular regulation, leading to recurring or chronic migraines.

The key takeaway is that you must have a formal diagnosis for both conditions — the VA won’t grant secondary service connection based on vague symptoms like back or knee pain.

Do You Need a Nexus Letter for Secondary Conditions?

By nature, most secondary conditions require a nexus letter because they aren’t documented during service, often develop years later, and may have other possible causes.

However, the stage of your VA claim when you get one matters. These are the points in the process when you should consider it.

Your C&P Exam Was Unfavorable

If your Compensation & Pension (C&P) exam didn’t support your claim, you need a nexus letter. The VA heavily relies on these for establishing service connection.

Example: Derrick filed a claim for migraines secondary to a traumatic brain injury, but the VA denied it after a negative C&P exam.

In this case, a nexus letter could challenge the and offer medical evidence linking his migraines to the TBI.

Weak Medical Link Between the Two Conditions

Some secondary conditions have stronger, more established medical links than others. Here are a few key things the VA looks for when deciding if the connection is valid.

3 Things That Strengthen a Medical Connection:

1. Established Medical Research:
   The VA gives more weight to conditions backed by long-standing, peer-reviewed studies rather than new or experimental research still being debated

2. Recognized Medical Literature & Guidelines:
   References from reputable sources like the Journal of the American Medical Association (JAMA), NIH, or UpToDate show that the relationship between conditions is widely accepted in the medical community.

3. Consistent Findings Across Multiple Studies:
   When several studies — across different researchers and years — point to the same conclusion, the connection is considered more reliable. The VA often views consistent findings as stronger than a single “breakthrough” paper.

For secondary claims especially, the nexus letter must explain why the medical literature applies to the veteran specifically and not just that a general correlation exists.

This is why generic nexus letters fail in secondary claims, because each medical connection is complex and can look different for every veteran.

Your Condition Has Many Alternative Causes

When reviewing secondary claims, the VA often looks for other possible explanations for your condition:

1. Lifestyle Factors:
   Things like weight gain, smoking, alcohol use, or lack of exercise that could explain the condition without linking it to a service-connected disability.

2. Age or Natural Progression:
   The VA often argues that a condition developed naturally over time or worsened due to aging, not because of another service-connected issue.

3. Non-Service-Related Injuries or Illnesses:
   Any separate accident, illness, or medical condition that could independently cause the problem — breaking the chain between your two claimed conditions

Sleep apnea often has numerous alternative causes, so a nexus letter must thoroughly address all of them.

What Do You Need to Prove Secondary Connection?

To prove a secondary service connection, there are a few key things to understand. Pay close attention to this section, since many veterans overlook these important details.

Diagnosis from a Doctor/Specialist

The first step in proving a secondary service connection is obtaining a clear diagnosis from a qualified medical professional.

1. Get a formal diagnosis from a specialist with expertise in the condition.

2. Provide the date of diagnosis and method used.

3. Include the credentials of the specialist.

A proper diagnosis lays the foundation for your claim and ensures the VA recognizes the condition as legitimate.

Clear Timeline of Symptoms

Show when your symptoms began and how they developed over time.

1. Record onset and progression of your secondary condition.

2. Include medical documentation of symptoms.

3. Explain how the condition has impacted your life in measurable terms.

If medical documentation is limited, buddy and lay statements can help establish your symptom timeline.

Medical Evidence or Rationale Linking the Conditions

Provide medical support explaining why the secondary condition is connected to your service-connected condition.

Good examples include:

1. Medical literature showing the conditions are related

2. Studies or clinical guidelines supporting the link

3. Other medical reasoning connecting the two conditions

Citing credible studies or expert reasoning—for example, research showing a correlation between PTSD-related weight gain and sleep apnea—makes your nexus argument stronger and more credible to the VA.

VA Nexus Letter Example for a Secondary Condition

Below is typically what a nexus letter for secondary conditions will look like. Other examples may look slightly different, and you will need to make the appropriate changes.

Case: This example represents a fictional case of a veteran whose PTSD treatment with certain medications contributed to weight gain, resulting in obstructive sleep apnea (OSA).

Background Information

Dr. Sarah Thompson, M.D. (Board-Certified Sleep Specialist)
Restorative Sleep & Wellness Clinic
123 Health Way, Suite C, Richmond, VA 23225
Phone: (555) 987-6543
Email: sthompson@restorativesleepclinic.com
Date: October 17, 2025

Reference: Michael Thompson
Veterans VA File #: 987-65-4321

To Whom It May Concern:

I have evaluated and treated Sergeant First Class Michael Thompson for obstructive sleep apnea (OSA), which developed secondary to service-connected Post-Traumatic Stress Disorder (PTSD). I am a board-certified sleep specialist with over 12 years of experience diagnosing and managing sleep disorders.

Background on PTSD Condition

Mr. Thompson has been service-connected for Post-Traumatic Stress Disorder (PTSD) since 2010.

He has been treated with Sertraline and Prazosin, both associated with weight gain and metabolic changes.

Research supports this link — PTSD has been shown to contribute to increased body weight through stress-related hormonal and behavioral factors (Kubzansky et al., JAMA Psychiatry, 2014; Vieweg et al., J Clin Psychiatry, 2006).

This medical opinion first establishes the link between PTSD and weight gain, then explains how that weight gain contributed to the development of obstructive sleep apnea.

Diagnosis of Sleep Apnea

Mr. Michael Thompson was diagnosed with Obstructive Sleep Apnea (OSA) on April 12, 2021, after completing an overnight polysomnography (sleep study) at Thompson Sleep Center.

The results showed an Apnea-Hypopnea Index (AHI) of 28, confirming moderate OSA. His condition is listed under ICD-10 Code G47.33 – Obstructive Sleep Apnea (Adult).

Listing objective diagnostic criteria and specific test results increases the credibility of the medical opinion.

Symptom Timeline for Sleep Apnea

• 2019–2020: Loud snoring, restless sleep, and gasping for air during the night.
• 2021: Daytime tiredness, trouble focusing at work, and increased irritability.
• 2022–2023: Morning headaches and frequent awakenings despite using CPAP therapy.
• 2024–Present: Ongoing fatigue, short-term memory problems, and reduced motivation.

Providing a timeline with documentation strengthens the nexus by showing chronological causation.

Impact on Daily Life

• Daytime Drowsiness: Mr. Thompson experiences persistent daytime fatigue and difficulty staying awake while driving or performing routine tasks, indicating ongoing sleep disruption and impaired alertness.
• CPAP Use: He requires nightly CPAP therapy to maintain airway patency and prevent apneic events. Despite consistent use averaging 6 hours per night, compliance data show only partial symptom relief, with continued reports of daytime tiredness and reduced energy.

When describing functional impact, it’s important to explain how the symptoms align with specific VA rating criteria.

Evidence Reviewed

• Service Treatment Records (STRs): PTSD documentation
• VA Medical Records: Ongoing treatment notes
• C&P Exam Reports: Prior PTSD evaluations
• Sleep Study Results: Confirmed OSA diagnosis
• Medication History: Sertraline and Prazosin use
• Progress Notes: Weight tracking over time
• CPAP Compliance Data: Therapy adherence review
• Lab Reports: Metabolic and thyroid panels
• Lay Statements: Veteran symptom descriptions
• Medical Literature: Studies linking PTSD to weight gain

Addressing prior C&P exams prevents common reasons for claim denial. Many VA claims are denied simply because prior C&P exams or existing medical evidence are not directly addressed

Medical Rationale

Excess body weight is a well-established risk factor for obstructive sleep apnea. Increased fat deposition around the neck, pharynx, and upper airway can narrow the airway and promote obstruction during sleep. Research consistently shows that even modest weight gain can significantly raise the risk and severity of OSA.

• Young et al., New England Journal of Medicine, 2002: Identified obesity as the strongest modifiable predictor of OSA.
• Peppard et al., American Journal of Epidemiology, 2000: Found that a 10% weight gain results in a six-fold increase in OSA risk.
• Newman et al., Sleep, 2005: Demonstrated that higher BMI correlates directly with increased apnea-hypopnea index (AHI) scores.

Mr. Thompson’s documented weight increase from 178 lbs to 214 lbs over 15 years represents a clinically significant change that, based on established medical literature, substantially elevates the likelihood and severity of OSA.

Linking medication side effects to secondary medical conditions establishes a plausible causal pathway.

Ruling Out Other Causes

• Cardiac conditions: No evidence of heart failure or related issues.
• Smoking history: Denies any tobacco use.
• Alcohol use: Occasional and not clinically significant.
• Drug use: Denies sedative or illicit substance use.
• Medications: No agents known to suppress respiration identified.
• Lifestyle factors: Maintains moderate activity level; does not engage in shift work.
• Family history: No known familial sleep or breathing disorders.

Eliminating alternative causes ensures the “at least as likely as not” standard is satisfied.

Conclusion

Based on my review and clinical evaluation, it is my professional opinion that Sergeant First Class Michael Thompson’s obstructive sleep apnea is at least as likely as not (50% or greater probability) caused or aggravated by his service-connected PTSD and related weight gain from PTSD medications.

Sincerely,

Dr. Sarah Thompson, M.D.
Board-Certified Sleep Specialist
Restorative Sleep & Wellness Clinic

Final Thoughts on Nexus Letters for Secondary Conditions

Understanding how nexus letters work for secondary conditions gives veterans a clear path to strengthening their VA claim.

A well-written nexus letter links your service-connected disability to a new or aggravated condition and provides the medical proof the VA needs to grant approval.

Once you know when you need one, the next step is learning how to get a nexus letter the right way. With the right doctor, a clear diagnosis, and strong medical reasoning, you can build powerful evidence that greatly improves your chances of receiving the benefits you’ve earned

FAQ

• Is a nexus letter required for secondary conditions?

  Most of the time, you’ll need a nexus letter for secondary conditions. If your C&P exam was unfavorable or the medical connection between your conditions is weak, a nexus letter is almost always required

• Do I need a nexus letter for sleep apnea secondary to PTSD?

  For secondary conditions like sleep apnea linked to PTSD, the connection is usually not strong enough for the VA to grant benefits automatically. In these cases, you almost always need a nexus letter to make your claim

• How to prove secondary service connection?

  To prove a secondary connection, you need to show that your secondary condition developed as a result of your primary service-connected condition. This usually involves documenting a clear symptom timeline, ruling out other possible causes, and providing a medical explanation—often through a nexus letter—that links the two conditions