Myositis-Related Interstitial Lung Disease: A Respiratory Physician's Point of View

Abstract

Idiopathic inflammatory myositis (IIM) is an umbrella term for diseases of unknown origin that cause muscle inflammation. Dermatomyositis and polymyositis are IIMs that commonly cause interstitial lung disease (ILD). When a patient presents with ILD, the evaluation of whether the case displays the characteristics of myositis should be determined by interview, physical examination, imaging findings, the measurement of myositis-related antibodies, and the determination of disease severity after diagnosis. Rapidly progressing anti-melanoma differentiation-associated gene 5 antibody-positive ILD may require rapid multi-drug therapy, while anti-aminoacyl tRNA synthetase (ARS) antibody-positive ILD can be treated with anti-inflammatory drugs. Importantly, however, anti-ARS antibody-positive ILD often recurs and sometimes develops into fibrosis. Early diagnosis is crucial for treatment, and we therefore need to clarify the features of myositis associated with ILD and suspect these pathologies early. This section reviews what clinicians need to look for and what findings are evaluated in patients when diagnosing myositis associated with ILD.

Keywords: anti-ARS antibody; anti-MDA5 antibody; dermatomyositis; polymyositis; progressive fibrosing interstitial lung disease; rapid progressive interstitial lung disease.

Figure 1

Skin manifestations of PM/DM. (a) Heliotrope rash. (b) Gottron’s sign. (c) Nail fold bleeding. (d) Raynaud’s phenomenon. (e) Anti-synthetase syndrome is often associated with mechanic’s hand. (f,g) Anti-MDA5 antibody-positive dermatomyositis is often associated with reverse Gottron’s sign (f), ulceration, and gangrene (g).

Figure 2

CT findings of anti-ARS antibody-positive ILD. (a) Prednisolone was administered, dense shadows along the bronchial vascular bundles improved, and prednisolone was discontinued after about 10 years. (b) Prednisolone and tacrolimus treatment left mild fibrosis after 4 years. (c) Prednisolone and cyclosporine A treatment achieved temporary improvement after 4 months, but fibrosis worsened after about 13 years.

Figure 3

Classification tree for subgroups of adult myositis-related interstitial lung disease (ILD). A patient must first meet the EULAR/ACR classification criteria for inflammatory myopathies (IIM). The patient can then be sub-classified using the classification tree (modified from the figure in Reference [5]). ARS, aminoacyl-tRNA synthetase; ab, antibody; MDA5, melanoma differentiation-associated gene 5; IBM, inclusion body myositis; PM, polymyositis; DM, dermatomyositis; ADM, amyopathic dermatomyositis.