Our study suggests that there is a strong association between constrictive bronchiolitis and exercise limitation in a cohort of soldiers who served in the Middle East. Constrictive bronchiolitis, a very rare finding in otherwise healthy, young adults, is most commonly reported in patients with rheumatologic disorders or in those who have undergone organ transplantation. The disorder is also associated with inhalational exposure to nitrogen dioxide, sulfur dioxide, inorganic dust, fly ash, and the diacetyl used in the manufacture of microwave popcorn.15-20
The majority of biopsy samples obtained from soldiers in our study showed polarizable material consistent with the inhalation of particulate matter, even though most of the soldiers were lifelong nonsmokers. Most of the biopsy samples also showed thickening of the arteriolar wall or occlusion in adjacent arterioles, a finding also seen with toxic inhalation.21
The soldiers who were initially evaluated in this series had prolonged exposure to toxic levels of sulfur dioxide associated with the Mosul sulfurmine fire, and we expected that the finding of constrictive bronchiolitis would be limited to this group. Over time, however, a number of soldiers without exposure to the sulfur-mine fire presented with similar exercise limitations. This group causes particular concern, since their potential toxic exposures are shared by most personnel who were deployed to Iraq and Afghanistan. These common exposures include open-air burn pits, in which solid waste was routinely incinerated in close proximity to living quarters, and desert dust storms of such severity that they obscured visibility. The presenting symptoms, smoking histories, evaluations, and biopsy samples of the 10 soldiers who did not report exposure to the sulfurmine fire were indistinguishable from those of the 28 soldiers who did report such exposure.
The diagnosis of constrictive bronchiolitis is challenging, especially in the absence of known predisposing conditions. Typically, patients have nonspecific respiratory symptoms and have an exercise limitation that is disproportionate to findings on pulmonary-function testing,15,16,21
which are frequently normal or mildly abnormal with both obstructive and restrictive patterns.17
In the soldiers in our study, results on pulmonary-function testing tended toward the lower limit of the normal range, as compared with population control subjects, but were significantly lower than those in a group of historical military control subjects.9
Ideally, we would have compared pulmonary function before deployment with measures after deployment, but only one of the soldiers in our study had undergone spirometry before deployment. His post-deployment FEV1
and FVC measurements were much lower than his predeployment values, with the FEV1
dropping from 5.09 liters to 3.91 liters (a decrease from 116% to 94% of the predicted value) and the FVC dropping from 5.77 liters to 4.58 liters (a decrease from 107% to 89% of the predicted value). Despite this accelerated decline in lung function, the results of post-deployment pulmonary-function testing remained within the normal range for this soldier.
Radiologic imaging generally did not suggest the presence of constrictive bronchiolitis among the soldiers in our study. Only a few soldiers had high-resolution CT showing the centrilobular nodularity or expiratory air trapping that can be associated with constrictive bronchiolitis. Several studies have reported normal imaging in patients with constrictive bronchiolitis because of the absence of associated alveolar disease.22-25
We cannot estimate the absolute prevalence of histologic bronchiolitis among soldiers, since the results of analyses of biopsy samples from an asymptomatic group of soldiers who have served in the theater of war have not been reported. The comparison between findings in the soldiers in our study and those in historical military controls is weakened because the control group was slightly younger and had a lower mean body-mass index than the soldiers in our study, a limitation that was attenuated by comparisons of the percent predicted values for the two groups. Despite these differences in demographics, the comparisons between the soldiers in our study and historical military control subjects were more appropriate than comparisons with the general population, given the standards of physical fitness required by military service.
Additional studies are needed to evaluate the particulate matter observed in many biopsy samples obtained from these soldiers. The correlation between the composition of the particulate matter with environmental exposures could lead to enhanced protective measures for soldiers in future deployments in the Middle East and elsewhere.
In summary, we found a high prevalence of constrictive bronchiolitis, an otherwise rare illness, in the 80 soldiers we evaluated. Evaluation for constrictive bronchiolitis should be considered among returning veterans who report having exercise limitations and who have essentially normal results on imaging and physiological studies.