Computed Tomographic Imaging in Connective Tissue Diseases

Joseph Barnett, FRCR; Anand Devaraj, MD, MRCP, FRCR

Disclosures

Semin Respir Crit Care Med. 2019;40(2):159-172. 

In This Article

Polymyositis/Dermatomyositis

Polymyositis (PM) and dermatomyositis (DM) are idiopathic inflammatory myopathies affecting proximal skeletal muscle, and are distinguished by the presence of characteristic skin lesions. Systemic involvement most commonly involves the esophagus, heart, and lungs, specifically as an ILD. A proportion of patients with PM/DM are further classified as having an "antisynthetase" syndrome, on the basis of specific autoantibodies to aminoacyl-transfer ribonucleic acid synthetase (the most frequent being Jo-1). This syndrome is associated with more severe myositis and ILD, which occurs in the majority of patients.[113] A rare subtype of DM deserves special mention: Clinically hypomyopathic DM is a disease which presents primarily with a rapidly progressive ILD, associated with autoantibodies to melanoma differentiation-associated gene 5 (MDA-5).

Parenchymal Disease

The ILD in patients with PM/DM has been described as a "fibrotic OP"[114] or an "NSIP/OP overlap."[58] Radiologically, this entity is characterized in the acute phase as an OP, which has variable appearances including peripheral or peribronchial consolidation, sometimes demonstrating a perilobular or halo morphology. This can progress to an NSIP pattern of fibrosis, which is often bronchocentric, and can consist of reticulation, ground-glass opacity, or a combination of the two. Honeycomb cyst formation is uncommon[115] (Figure 5). HRCT UIP morphology is occasionally described in PM/DM,[115] but should prompt careful clinical scrutiny for features of overlap with RA.

Figure 5.

A patient with dermatomyositis and interstitial lung disease. Features of NSIP are present, including a ground-glass infiltrate containing fine reticulation and marked lower lobe volume loss as evidenced by the position of the major fissures. There is superadded consolidation, which in places has a perilobular distribution. The constellation of HRCT findings is termed NSIP/OP overlap. HRCT, high-resolution computed tomography NSIP, nonspecific interstitial pneumonia; OP, organizing pneumonia.

It must be noted, however, that the phenotype of PM/DM is variable, depending at least in part on the specific autoantibody present. NSIP and NSIP/OP overlap are the hallmark of antisynthetase syndromes; in patients with anti-MDA-5 autoantibodies, OP and consolidation are the most common findings (Figure 6).[115] Pneumothorax and pneumomediastinum are also associated HRCT findings.[116]

Figure 6.

Patient with a clinically hypomyopathic myositis. Initial CT (left column) performed due to shortness of breath demonstrates peripheral consolidation and ground-glass opacity with a perilobular distribution. No fibrosis is evident. CT performed 2 months later due to acute respiratory failure (center column) reveals an established fibrotic interstitial lung disease, with traction bronchiectasis and consolidation in the left lower lobe (top image), pneumomediastinum and upper lobe (bottom image) ground-glass infiltrate. Images performed 1 year later (right column) show resolution of the lower lobe consolidation, but a persisting fibrotic interstitial lung disease, characterized by ground-glass opacity admixed with fine reticulation. The subpleural lung in the left lower lobe is spared. CT, computed tomography.

Clinical Significance

A strong association between autoimmune myositis and ILD has long been established, and many centers practice routine screening of the lungs for ILD. ILD per se in PM/DM is a significant cause of mortality, identification of disease phenotype can also be used to predict disease behavior. The presence of a HRCT UIP pattern, in particular, is associated with a progressive disease course.[117] As in other conditions, acute exacerbations are also implicated in increased mortality.[118] Conversely, a significant proportion of patients with ILD can experience resolution or stabilization of PM/DM ILD; these patients are characterized by OP and NSIP patterns of disease,[117] with one large cohort of patients with antisynthetase syndrome-associated ILD having 10-year survival of 68%.[119]

HRCT also offers important diagnostic information in PM/DM. The presence of a rapidly progressive consolidative interstitial pneumonia should prompt the radiologist to raise the possibility of a clinically hypomyopathic DM, a disease which may not be apparent on clinical examination and lies outside the normal panel of autoantibodies screened for CTD. This disease is associated with significant 90-day mortality.[120]

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