Pulmonary emphysema subtypes on computed tomography: the MESA COPD study

Abstract

Background: Pulmonary emphysema is divided into 3 major subtypes at autopsy: centrilobular, paraseptal, and panlobular emphysema. These subtypes can be defined by visual assessment on computed tomography (CT); however, clinical characteristics of emphysema subtypes on CT are not well defined. We developed a reliable approach to visual assessment of emphysema subtypes on CT and examined if emphysema subtypes have distinct characteristics.

Methods: The Multi-Ethnic Study of Atherosclerosis COPD Study recruited smokers with chronic obstructive pulmonary disease (COPD) and controls ages 50-79 years with ≥ 10 pack-years. Participants underwent CT following a standardized protocol. Definitions of centrilobular, paraseptal, and panlobular emphysema were obtained by literature review. Six-minute walk distance and pulmonary function were performed following guidelines.

Results: Twenty-seven percent of 318 smokers had emphysema on CT. Interrater reliability of emphysema subtype was substantial (K: 0.70). Compared with participants without emphysema, individuals with centrilobular or panlobular emphysema had greater dyspnea, reduced walk distance, greater hyperinflation, and lower diffusing capacity. In contrast, individuals with paraseptal emphysema were similar to controls, except for male predominance. Centrilobular, but not panlobular or paraseptal, emphysema was associated with greater smoking history (+21 pack-years P <.001). Panlobular, but not other types of emphysema, was associated with reduced body mass index (-5 kg/m(2); P = .01). Other than for dyspnea, these findings were independent of the forced expiratory volume in 1 second. Seventeen percent of smokers without COPD on spirometry had emphysema, which was independently associated with reduced walk distance.

Conclusions: Emphysema subtypes on CT are common in smokers with and without COPD. Centrilobular and panlobular emphysema, but not paraseptal emphysema, have considerable symptomatic and physiological consequences.

Keywords: Centrilobular; Computed tomography; Emphysema; Panlobular; Paraseptal.

FIGURE 1. Reference Images for Absence of Emphysema and Emphysema Subtypes

Axial CT images were selected from training set scans in which all four raters independently agreed on the absence or isolated presence of each emphysema subtype. A. Absence of emphysema; B. Centrilobular emphysema; C. Paraseptal emphysema; D. Panlobular emphysema. Abbreviation: CT denotes computed tomography.

FIGURE 2. Proportions of MESA COPD Study Participants with One or Multiple Subtypes of Emphysema

Presence of each emphysema subtype was defined as ≥1% of the lung volume affected. Proportions are weighted to reflect distribution in the source population (see methods for details). Abbreviations: MESA denotes Multi-Ethnic Study of Atherosclerosis, and COPD chronic obstructive pulmonary disease.

FIGURE 3. Male Gender, Body Mass Index and Pack-Years of Smoking among MESA COPD Study Participants by Emphysema Subtype

*Indicates p<0.05 for bivariate comparison of emphysema subtype versus control group (no emphysema) adjusted for multiple subtype comparisons using Dunnett’s procedure. Pack-years, gender prevalence, and body mass are weighted to reflect distribution in the source population (see methods for details). A. Pack-years of smoking; B. Gender; and C. Body mass index. Abbreviations: MESA denotes Multi-Ethnic Study of Atherosclerosis, COPD chronic obstructive pulmonary disease.

FIGURE 3. Male Gender, Body Mass Index and Pack-Years of Smoking among MESA COPD Study Participants by Emphysema Subtype

*Indicates p<0.05 for bivariate comparison of emphysema subtype versus control group (no emphysema) adjusted for multiple subtype comparisons using Dunnett’s procedure. Pack-years, gender prevalence, and body mass are weighted to reflect distribution in the source population (see methods for details). A. Pack-years of smoking; B. Gender; and C. Body mass index. Abbreviations: MESA denotes Multi-Ethnic Study of Atherosclerosis, COPD chronic obstructive pulmonary disease.

FIGURE 3. Male Gender, Body Mass Index and Pack-Years of Smoking among MESA COPD Study Participants by Emphysema Subtype

*Indicates p<0.05 for bivariate comparison of emphysema subtype versus control group (no emphysema) adjusted for multiple subtype comparisons using Dunnett’s procedure. Pack-years, gender prevalence, and body mass are weighted to reflect distribution in the source population (see methods for details). A. Pack-years of smoking; B. Gender; and C. Body mass index. Abbreviations: MESA denotes Multi-Ethnic Study of Atherosclerosis, COPD chronic obstructive pulmonary disease.

FIGURE 4. Prevalence of Predominant Emphysema Subtypes among MESA COPD Study Participants by COPD Severity

Predominant emphysema subtype was defined as the subtype affecting the greatest percentage of lung in each participant and severity of COPD was defined by GOLD spirometric criteria. Proportions are weighted to reflect distribution in the source population (see methods for details). Abbreviations: MESA denotes Multi-Ethnic Study of Atherosclerosis, COPD chronic obstructive pulmonary disease, GOLD global initiative for chronic obstructive lung disease.