The chest CT above demonstrates traction bronchiectasis, interstitial
fibrosis and diffuse ground glass opacities consistent with a
non-specific interstitial pneumonia (NSIP) radiographic pattern. This
is most likely secondary to the development of interstitial lung disease
in this patient with known dermatomyositis.
Discussion
This patient presented with rapidly progressive interstitial lung
disease (ILD) and hypoxic hypercarbic respiratory failure in the setting
of a recent diagnosis of dermatomyositis (DM).
This high-resolution CT scan demonstrates several features of ILD:
- a reticular interstitial pattern with a mesh of overlapping linear opacities (e.g. right posterior portion)
- areas of ground glass opacities with a hazy appearance of preserved structures (e.g. anteromedial portions bilaterally)
- traction bronchiectasis with the "tram track" sign (e.g. right
anterior portion) that results as the airways fail to taper in the
periphery
This constellation of findings is consistent with NSIP, although
there is considerable overlap in radiologic findings in ILD and other
clinical data is needed for a complete diagnosis (1).
Bronchiectasis is defined as dilatation of the airways (bronchi =
airways; ectasia = dilation of a tube). Fibrosis in ILD causes decreased
parenchymal lung volumes and tissue retraction. The airways
subsequently experience an "outward" pull resulting in traction
bronchiectasis. In the absence of fibrosis and increased traction,
bronchiectasis can occur by either increased pressure within the airways
("pulsion") or decreased structural integrity. For example, "pulsion"
bronchiectasis can occur in allergic bronchopulmonary pneumonia as fungi
and mucous fills the proximal airways; primary bronchial weakness with
resultant bronchiectasis can be seen in Marfan syndrome (2). Cylindrical
bronchiectasis is less likely to demonstrate airway obstruction
compared to cystic bronchiectasis, although spirometric findings may
vary (3)
ILD occurs in approximately 40% of patients with DM, although
estimates vary from 20-80%. While DM-associated ILD usually progresses
slowly, certain phenotypes can progress rapidly. This is particularly
true in patients with amyopathic DM, which can result in substantial
morbidity and mortality. The pathophysiology is poorly understood, with
possible involvement of both cellular and humoral auto-immunity (4).
Case series suggest that DM-ILD most frequently demonstrates an NSIP
pattern on CT and biopsy (5).
Determining the etiology of dyspnea in patients with DM can be
challenging. In addition to ILD other possibilities such as respiratory
muscle weakness, drug-induced pneumonitis, and infection in the setting
of immunosuppression must be considered. For this patient time was of
the essence and five weeks of ongoing work-up may have precluded her
from receiving more aggressive immunosuppressive therapy prior to
respiratory failure, cardiac arrest, and death.
References
-
Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J.
Fleischner Society: Glossary of Terms for Thoracic Imaging. Radiology
2008; 246:697–722.
-
Chan ED, Iseman MD. Bronchiectasis. In Broaddus VC, Mason RJ, Ernst
JD, King TE, Lazarus SC, Murray JF, Nadel JA, Slutsky AS, Gotway MB,
eds: Murray and Nadel's Textbook of Respiratory Medicine. Sixth Edition.
Elsevier, 2016, pp. 853–876.
-
Alzeer A. HRCT score in bronchiectasis: Correlation with pulmonary
function tests and pulmonary artery pressure. Ann Thorac Med 2008; 3:82.
-
Connors GR, Christopher-Stine L, Oddis C V, Danoff SK. Interstitial
lung disease associated with the idiopathic inflammatory myopathies:
what progress has been made in the past 35 years? Chest 2010;
138:1464–1474.
-
Douglas WW, Tazelaar HD, Hartman TE, Hartman RP, Decker PA, Schroeder
DR, Ryu JH. Polymyositis-dermatomyositis-associated interstitial lung
disease. Am J Respir Crit Care Med 2001; 164:1182–1185.
