Pathology of the lung in myositis

Epidemiology of lung involvement in autoimmune myositis Th e interstitial lung diseases (ILDs) encompass a large number of distinct disorders that are characterized by infl ammation and/or fi brosis involving the lung parenchyma. Th ese disorders result from a myriad of potential etiologies including medications, environmental exposures and autoimmune diseases such as myositis. Regardless of etiology, these lung injuries result in a limited number of patterns that are classifi ed based on pathologic appearance into several major subgroups (Table 1). In general, the pathology impacts prognosis regard less of the etiology of the ILD. Th e target of injury includes the critical alveolar–capillary interface respon sible for gas exchange. As a group, therefore, ILDs result in compromised oxygen absorption as well as decreased lung compliance and increased work of breathing. Th e clinical manifestation of ILD is typically dyspnea on exertion, cough and fatigue. Lung involvement in autoimmune myositis was fi rst systematically reviewed in 1974 [1], although it had been described in individuals and case series since the mid1960s. Since that time, there has been an increasing appreciation of the prevalence and clinical signifi cance of ILD. Recent studies suggest that ILD complications occur in 20 to 65% of individuals with myositis (reviewed in [2]). Th e wide variation in prevalence refl ects in part the lack of a standard approach to screening for ILD in newly diagnosed patients with myositis. A recent study of 90 histidyl-tRNA synthetase (Jo-1) patients found ILD present in 86% [3]. Alanyl-tRNA synthetase (PL-12) is similarly associated with ILD in 90% or more of patients based on two recent case series [4,5]. Th e apparently increasing rates of ILD in patients with myositis represent a combi nation of improved diagnostic techniques and increasing awareness of ILD as a presenting symptom of auto immune myositis. Th e mortality associated with ILD has been anecdotally described since the earliest reports. Prospective long-term studies suggest a 40% increase in mortality attributable to ILD [6]. ILD is thus both a common and a highly lethal manifestation of autoimmune myositis.