The human lung branches from the trachea down through progressively smaller airways until it reaches the bronchioles — airways about 2 millimeters or less in diameter — where oxygen exchange ultimately occurs. Constrictive bronchiolitis (CB) is a pathological process in which fibrous scar tissue progressively fills and constricts these tiny airways, eventually obliterating them entirely. Because gas exchange cannot occur through scar tissue, affected areas of lung cease to function.
Unlike obstructive lung diseases such as asthma, where airway narrowing is caused by inflammation and smooth muscle spasm that can be reversed with bronchodilators, the scarring in CB is permanent and irreversible. There are no medications that reverse established CB. Management focuses on preventing further progression, optimizing remaining lung function, and treating symptoms.
The link between military service in Iraq and Afghanistan and constrictive bronchiolitis was documented as early as 2011, when pulmonologist Dr. Robert Miller and colleagues at Vanderbilt University published findings in the New England Journal of Medicine reporting CB in soldiers from Fort Campbell, Kentucky who had deployed to Iraq and Afghanistan and returned with unexplained dyspnea on exertion — despite normal or near-normal chest CTs and spirometry.
Crucially, every soldier with biopsy-confirmed CB in the initial series had significant exposure to airborne hazards during deployment — primarily through open burn pits, which burned waste including plastics, medical waste, chemicals, and human remains. Particulate matter from burn pit smoke, combined with desert dust, vehicle exhaust, and industrial pollution, created a toxic aerosol environment to which service members were exposed for months to years.
Subsequent research has confirmed the association, though the precise mechanism — whether it is specific chemicals, particulate size, immune dysregulation, or a combination — remains under investigation. What is not disputed is that veterans who served downwind of large burn pit operations at bases like Joint Base Balad, Camp Victory, and dozens of other locations across Iraq, Afghanistan, and Southwest Asia have experienced CB at rates that cannot be explained by chance.
Many veterans with CB spend years being treated for asthma before receiving the correct diagnosis. The key distinguishing features:
| Feature | Asthma | Constrictive Bronchiolitis |
|---|---|---|
| Response to bronchodilators | Significant improvement | Little to no improvement |
| Spirometry (PFTs) | Often shows obstruction | Often normal or near-normal |
| Exercise tolerance test | May show limitation | Often severely limited despite normal PFTs |
| Chest CT | May show air trapping or hyperinflation | Often normal; may show mosaic attenuation |
| Definitive diagnosis | Clinical + spirometry | Surgical lung biopsy |
| Reversibility | Partially reversible | Irreversible scarring |
| Treatment response | Good to steroids/bronchodilators | Poor |
The near-normal spirometry finding is particularly insidious. Veterans often present to VA C&P examiners with a complaint of debilitating breathlessness but walk away with a denial because "PFTs were within normal limits." The problem is that spirometry measures airflow through large airways — it is not sensitive to small airway disease until that disease is quite advanced. Veterans with CB can have normal PFTs because the large airways are unaffected even as the small airways are being destroyed.
The Sergeant First Class Heath Robinson Honoring our Promise to Address Comprehensive Toxics (PACT) Act of 2022, signed into law August 10, 2022, as Public Law 117-168, fundamentally changed the legal framework for post-9/11 veterans with toxic exposure-related conditions. Under the PACT Act:
38 CFR § 3.320 — Airborne hazards and open burn pit presumptions — lists constrictive bronchiolitis among the respiratory conditions presumptively associated with qualifying service. The full text of qualifying locations and service periods is codified in 38 CFR § 3.320(b). Veterans should specifically cite this regulation when filing claims for CB.
Practically, PACT Act presumptive status means VA must concede the nexus element of your claim if you have qualifying service and a confirmed CB diagnosis. This is a major shift from the pre-PACT era, when veterans had to produce independent medical opinions linking their specific burn pit exposures to their specific condition — a nearly impossible burden given the limited scientific literature at the time.
However, PACT Act status does not eliminate the need for a diagnosis. You still need a confirmed medical diagnosis of constrictive bronchiolitis. And because that diagnosis is difficult to obtain, many veterans with CB remain undiagnosed — and therefore unclaimed.
For veterans who have already been diagnosed with asthma under VA but believe they actually have CB, the PACT Act creates a pathway to reopen claims. A new diagnosis of CB — even if obtained after service — can be used to request a new claim or reopen a previously denied claim under the new presumptive framework.
Learn more about the broader PACT Act framework in our guide: PACT Act Presumptive Conditions: Complete 2026 Guide.
Of all the barriers veterans with constrictive bronchiolitis face, the diagnostic barrier is often the highest. Unlike most VA-ratable conditions where a clinical diagnosis from a treating physician is sufficient, CB's distinctive features make definitive diagnosis technically demanding.
The evaluation pathway for most patients with unexplained dyspnea begins with spirometry (PFTs), chest X-ray, and chest CT. In CB:
Cardiopulmonary exercise testing (CPET) is a critical but underutilized tool in post-deployment lung disease evaluation. Many veterans with CB show a pattern on CPET that is consistent with ventilatory limitation or abnormal ventilatory mechanics — revealing significant exercise intolerance despite "normal" spirometry. Veterans who have been told their lungs are normal but experience debilitating breathlessness on exertion should specifically request CPET as part of their workup.
Definitive diagnosis of constrictive bronchiolitis requires surgical lung biopsy — specifically video-assisted thoracoscopic surgery (VATS) with resection of a representative lung segment. The pathologist examines the biopsy under microscopy looking for the classic finding: concentric fibrous tissue deposited beneath the bronchiolar epithelium, narrowing or obliterating the bronchiolar lumen, without the luminal inflammatory exudate seen in proliferative bronchiolitis.
This is a real surgical procedure with real risks — general anesthesia, chest incision, potential for complications. VA cannot require you to undergo invasive testing. But if you want the definitive diagnosis, biopsy is currently the only way to confirm it with certainty.
The landmark cases that established the CB-burn pit link — published by Dr. Miller's group at Vanderbilt — were all biopsy-confirmed. VA is most likely to grant PACT Act claims for CB when the diagnosis rests on biopsy pathology.
Some veterans have obtained service connection for CB based on clinical diagnosis without biopsy, supported by: a consistent clinical picture (post-deployment onset of exercise-limiting dyspnea), exposure history (documented burn pit proximity), abnormal CPET, and exclusion of other causes. A pulmonologist experienced with post-deployment lung disease willing to render a clinical diagnosis of CB — and document it thoroughly — can support a viable claim even without biopsy. However, the evidentiary bar is higher and VA denial rates are higher without pathological confirmation.
Many VA contract C&P examiners are general internists or family medicine physicians with limited experience in post-deployment lung disease. A veteran presenting with CB may receive an inadequate exam or an opinion based primarily on normal PFTs. If your C&P examiner does not appear familiar with constrictive bronchiolitis, request a pulmonology consult. Always submit your own medical evidence and nexus letter rather than relying solely on VA's examination.
There is no Diagnostic Code specifically for constrictive bronchiolitis in 38 CFR Part 4. Under 38 CFR § 4.27, when a condition is not listed, it is rated by analogy to the most closely analogous listed condition that best reflects the nature and severity of the disability. For CB, VA typically rates by analogy to one of the following:
| FEV1 (% of predicted) | FEV1/FVC Ratio | Rating |
|---|---|---|
| Less than 40% | Less than 40% | 100% |
| 40%–55% | 40%–55% | 60% |
| 56%–70% | 56%–70% | 30% |
| 71%–80% | 71%–80% | 10% |
| Criteria | Rating |
|---|---|
| FEV1 less than 40% predicted; or; more than 1 attack per week with episodes of respiratory failure; or; daily use of systemic high-dose corticosteroids | 100% |
| FEV1 of 40%–55% predicted; or; more than once monthly attacks; or; oxygen therapy required | 60% |
| FEV1 of 56%–70% predicted; or; daily inhalational therapy; or; monthly attacks | 30% |
| FEV1 of 71%–80% predicted; or; inhalational therapy needed more than once weekly | 10% |
An important strategic consideration: because CB is rated by analogy, your attorney or VSO representative should argue for rating under whichever DC produces the higher rating based on your actual clinical picture. If your CB predominantly produces fixed airflow obstruction measurable by FEV1, DC 6604 may be more favorable. If your CB produces episodic exacerbations requiring medical care, DC 6602 may support a higher rating. The choice of analogous DC can significantly affect your final rating.
38 CFR § 4.97, Note (e) provides that when DC 6604 applies, DLCO (carbon monoxide diffusing capacity) may also be evaluated, and the veteran receives the higher evaluation. If your CB has caused a significant reduction in DLCO — which measures the lung's ability to transfer oxygen into the bloodstream — this should be specifically documented in your claim and C&P exam.
Veterans with severe CB that prevents substantially gainful employment may qualify for Total Disability based on Individual Unemployability (TDIU) under 38 CFR § 4.16. If CB alone is rated at 60% or higher, or if combined ratings meet the multi-disability threshold (70% combined with one condition at 40%+), TDIU is available.
On your VA Form 21-526EZ and in any cover letter, explicitly state: "I am filing this claim under the PACT Act of 2022, Public Law 117-168, and 38 CFR § 3.320, for constrictive bronchiolitis related to airborne hazard and open burn pit exposure during my service in [location] from [dates]." Explicit citation ensures the claim is routed to raters familiar with PACT Act processing and reduces the chance of a boilerplate denial on nexus grounds.
Under the PACT Act presumptive framework, veterans with qualifying service should not need an independent nexus letter — the law presumes the connection. In practice, VA sometimes still issues inadequate exams or denials that treat CB as if it requires individual nexus. In those situations, a nexus letter from a qualified pulmonologist becomes essential.
A nexus letter for constrictive bronchiolitis should:
REE Medical works with pulmonologists and internal medicine physicians who understand post-deployment lung disease and VA adjudication standards. If your claim has been denied or you need independent medical opinion support:
Need a Nexus Letter for Constrictive Bronchiolitis?
REE Medical connects veterans with physicians experienced in post-deployment respiratory conditions. Their nexus letters document the CB-burn pit scientific link, review your diagnostic workup, and provide the medical rationale VA raters need to grant PACT Act claims.
Learn About Nexus Letters for Respiratory Claims →claim.vet may receive a referral fee if you use this link. Veterans never pay more.
The C&P exam for a respiratory claim is different from a routine medical appointment. You are being evaluated for disability — emphasize what you cannot do, not what you can do.
Severe constrictive bronchiolitis can cause or worsen several conditions that are ratable as secondary to the primary CB diagnosis:
Also see our related guide on burn pit exposure claims: Burn Pit Exposure VA Claims: PACT Act Filing Guide.
PACT Act claims for constrictive bronchiolitis should be granted for veterans with qualifying service and a confirmed diagnosis. But denials happen — often due to:
If your claim is denied, you have three appeal lanes under the Appeals Modernization Act (AMA): Supplemental Claim (add new evidence, including a formal CB diagnosis or pulmonologist nexus letter), Higher-Level Review (senior rater review of existing record), or Board of Veterans' Appeals (BVA) appeal. For CB claims, the Supplemental Claim lane with a comprehensive nexus letter is often the fastest path to reversal when the initial denial was based on an inadequate examination.
Veterans seeking representation for PACT Act denials may benefit from a free initial review of their claim history:
Understand your options before the appeal deadline. Free claim review — no phone calls required.
Start My Free Claim Review — No Phone Required →Editorial Standards: Written by Marcus J. Webb, veterans benefits researcher. Verified against current 38 CFR regulations and PACT Act provisions. Last reviewed: July 2026. Not legal advice — for representation, talk to a VA-accredited attorney.