In US patients, bronchiectasis has a specific etiology that usually can be determined, with ethnicity being a major influence.
In contrast to findings from previous investigations, new research suggests that bronchiectasis is not primarily idiopathic but rather has a specific cause that can be determined in a majority of cases. According to Pamela J. McShane, MD, and colleagues from the University of Chicago Medical Center, causative factors are significantly influenced by ethnicity.
“Bronchiectasis has many causes, some of which are treatable,” the researchers noted. Previous studies have involved cohorts from single centers within the UK, they added.
Included in the current study were bronchiectasis patients at a university referral center without cystic fibrosis, emphysema, or interstitial lung disease. Each patient was administered a questionnaire assessing demographics, medication use, use of tobacco and alcohol, travel history, occupational and environmental exposures, and medical history, including clinical features of bronchiectasis. Pulmonary function was measured as per American Thoracic Society guidelines. In addition, all patients underwent high-resolution CT scanning.
The investigators reviewed microbiologic results of sputum and bronchoalveolar lavage samples obtained prior to study entry. Sputum also was obtained at the time of study entry, during follow-up visits, and during exacerbations. Plasma quantitative immunoglobulin levels were among the laboratory data obtained.
A total of 106 patients (mean age, 61.4; women, 71.4%) were included in the complete analysis. With regard to ethnicity, 60 subjects were European American, 30 were African American, 10 were Hispanic American, and three were Asian American. Among African American patients, BMI was significantly higher than for other ethnic groups. Demographic and clinical symptoms were not statistically different among the ethnic groups.
Identification in More Than 90% of Cases
“Prior investigations into the etiology of bronchiectasis have found that between 26% and 53% of cases are idiopathic, “ the study authors noted. “In contrast, only 6.6% of the present cases were idiopathic after systemic evaluation.”
Bronchiectasis was the result of immune dysregulation in 63.4% of all patients (eg, immune deficiency, autoimmunity, hematologic malignancy, and allergic bronchopulmonary aspergillosis). Aspiration (11.3%) and infection (mycobacterial, 9,4%; prior pneumonia, 9.4%) were among other common causes.
Nearly 29% of African American patients had bronchiectasis due to rheumatoid arthritis versus 6% of European patients. In European American patients, hematologic malignancy was the causative factor in 20% of cases versus 0% in African American patients. Significantly more Hispanic patients had Pseudomonas aeruginosa in their sputum compared with either African Americans or European Americans.
“An important new finding is the appreciable number (14%) of patients with hematologic malignancy or stem cell transplantation who developed bronchiectasis,” the researchers pointed out. “Although malignancy is a known cause of bronchiectasis, the exact pathogenesis is not defined. A central question is whether it is a manifestation of bronchiolitis obliterans resulting from graft versus host disease.” They also noted that six of 11 patients who received stem cell transplantation met criteria for bronchiolitis obliterans diagnosis.
The researchers acknowledged that their observational study of a single referral-based center is hypothesis generating. In addition, they allowed that the autoimmune features present in 12.3% of patients in the study may be coincidental and not the cause of their bronchiectasis. However, adding these patients to the 6.6% of patients with an idiopathic cause is still less than the 53% of idiopathic bronchiectasis seen in previous investigations, they contended.
McShane PJ, Naureckas ET, Strek ME. Bronchiectasis in a diverse US population: effects of ethnicity on etiology and sputum culture. Chest. 2012;142(1):159-167.