Epidemiology

The true incidence of thoracic complications in IBD patients is unknown. There have been no screening tests performed on large populations of IBD patients. The proportion of IBD patients with subjective respiratory symptoms such as cough, sputum production, wheezing, or shortness of breath has been reported to be as high as 50%. One or more pulmonary function tests (PFTs) are abnormal in approximately 40% of IBD patients, with forced expiratory volume in 1 second (FEV₁), inspiratory vital capacity (IVC), or diffusion capacity (DLCO) showing a 10% to 30% reduction. Between 25% and 50% of asymptomatic IBD patients show abnormalities on high-resolution computed tomography (HRCT) scans. Often, the findings are subtle and include ground-glass opacities, mosaicism suggestive of air trapping, peripheral opacities, and cysts. At the other end of the spectrum are case reports and small series of patients with distinctive manifestations of thoracic involvement. These reports, accounting for 155 patients, were recently reviewed (see Suggested Readings). Although nothing is offered to calculate incidence or prevalence, significant symptomatic thoracic involvement by IBD probably is not a common event. However, it is common enough that physicians need to be cognizant of IBD to recognize it and prevent the potentially debilitating consequences of some of its forms.

The temporal relation of the thoracic manifestation to the bowel disease varies. Approximately 80% of patients have an established history of IBD, whereas in about 10% each, the thoracic symptoms precede the bowel disease or develop concomitantly. About one half of patients with airway disease have had a colectomy, and occasionally the onset of airway disease follows the colectomy by days or weeks, suggesting a shift of the inflammatory reaction from the gut to the bronchial tree.

In ulcerative colitis and Crohn disease, the most common anatomic structures involved are the large airways (39%), followed by infiltrative lung disease (23%) and involvement of the serosa (13%). Small airways inflammation (10%), upper airways inflammation (9%), and involvement of the pulmonary vasculature (6%) are slightly less common. In general, respiratory tract involvement is more common in UC than CD patients. In both diseases, however, all compartments of the respiratory tract can be affected, although with slight differences in incidence.

Severity of thoracic involvement in many cases parallels disease activity in the bowel. Patients with active IBD have a greater chance of exhibiting airway obstruction. Inflammation of the bowel also correlates inversely with diffusion capacity. Serosal disease is more common among those with active IBD, while parenchymal disease is often seen in patients with quiescent bowel disease.

Women appear to be more frequently affected (~2 : 1). When considering only airway disease, this ratio increases up to 4 : 1. However, pleural involvement is about equally distributed between women and men.

Two thirds of patients with thoracic complications also have other extraintestinal manifestations at the same time, such as involvement of the skin, eyes, joints, or the biliary tract. Smoking does not appear to be a risk factor for developing airway inflammation in IBD, because most patients with this manifestation are nonsmokers.

Interestingly, two recent analyses found that CD patients appear to have a slightly increased risk of lung cancer, whereas the risk appears to be decreased in UC patients (standardized incidence ratios of 1.82 vs. 0.39 and 0.72, respectively).

Clinical and Pathologic Features

The diagnostic workup should include chest radiograph and CT scan. PFTs should be obtained, if possible, because they can provide a baseline in the course of treatment. Endoscopy complements imaging studies in the detection of upper airway obstruction or stenosis and in obtaining material for microbiology and histologic studies. A complete blood count with differential as well as a metabolic panel should be performed. Erythrocyte sedimentation rate and C-reactive protein may be helpful in following disease activity during treatment. Between 50% and 70% of patients with ulcerative colitis and 10% to 30% of patients with Crohn disease (predominantly those with colonic involvement) show atypical antineutrophil cytoplasmic antibodies (ANCAs), characterized by a fine granular and perinuclear (“snowdrift”) pattern. Serologic testing for ANCAs may be helpful in patients with suspected underlying IBD. ANAs can help identify drug-induced lupus syndrome in patients with serositis. Since thromboembolic disease is a known cause of morbidity and mortality in IBD patients, the physician should maintain a low threshold to consider and exclude pulmonary embolism in this population.

This section discusses the different compartments of the respiratory tract involved by IBD, including unique considerations of the particular location, clinical presentation, and its pathologic features (Table 79-1).