22 Polymyositis/Dermatomyositis and the Lung

Polymyositis is a rare autoimmune disease, characterized by inflammation and degen- eration of the skeletal muscles. If the skin is involved it is called dermatomyositis (Figure 22.1a, b, c). The incidence is 2–6 patients per 1 million inhabitants. In polymyositis, clon- ally expanded CD8

cytotoxic T cells invade muscle fibers that express MHC class I anti- gens, which leads to fiber necrosis via the perforin pathway. Dermatomyositis is a microangiopathy affecting skin and muscle; activation and deposition of complement causes lysis of endomysial capillaries and muscle ischemia. The causative autoantigen has not yet been identified.

Pulmonary manifestations of polymyositis/dermatomyositis (PM/DM) are numerous and present in about 50% of patients. They intensely influence the outcome of the disease; the overall mortality is 24%, and in patients with pulmonary involvement it rises to 62%. Specific pulmonary manifestations are diverse (Table 22.1), but most frequent are interstitial changes due to nonspecific interstitial pneumonia, complications due to aspiration pneumonia secondary to pharyngeal and esophageal disorder, and hyposta- tic pneumonia and respiratory failure secondary to respiratory muscle dysfunction and hypoventilation. Opportunistic infections and drug-induced pneumonitis are consid- ered in differential diagnosis.

Interstitial lung disease is more frequent in women and can precede the onset of muscle or skin disease in 25% of cases. The initial symptoms are cough and dyspnea.

Plain radiograph of the chest reveals bilateral, lower lobe reticulonodular pattern (Figure 22.2), and HRCT scan reveals bibasilar septal thickening, ground-glass opacities, and consolidation (Figure 22.3). Honeycombing is quite rare. Lung function tests show restrictive ventilatory changes and reduced DLco. Respiratory muscle weakness is demonstrated by a decrease in maximal inspiratory pressure and flow rates. Patients who have PM/DM and interstitial lung disease have more frequently an extractable nuclear antigen to RNA synthetase that is called the Jo-1 antibody (Figure 22.4) than those without ILD. As the causes of pulmonary disease in PM/DM patients are diverse, bron- choscopy and lung lavage are aimed to solve the differential diagnosis, especially if opportunistic infection is assumed or if respiratory failure of undefined etiology develops. Open lung biopsy is seldom performed.

Progressive and nonprogressive disease needs to be distinguished by clinical and physiologic monitoring to avoid overtreatment. Patients with ongoing functional dete- rioration mostly benefit from aggressive therapy. Cyclophosphamide together with cor- ticosteroids is beneficial in many patients.

22

Polymyositis/Dermatomyositis and the Lung

125

126 Clinical Atlas of Interstitial Lung Disease

Figure 22.1. Gottron plaques, red-purple keratotic, atrophic erythema are found on the surface of finger joints, in this case most prominent over the metacarpophalangeal joints (a). A composite showing diffuse interstitial lung disease in a patient with der- matomyositis with violaceous or heliotrope rash of the face. The rash is named after the flower called Heliotrope because it follows the course of the sun (b). In this patient the skin rash is also located in a fairly characteristic distribution, including around the eyes and face, where it is edematous and red (c). Of note is that the skin lesions can occur well before the muscle manifestations.

Table 22.1. Pulmonary manifestations of polymyositis/dermatomyositis (PM/DM).

Frequency Parenchymal disease

Nonspecific interstitial pneumonia (NSIP) +++

Usual interstitial pneumonia (UIP) ++

Bronchiolitis obliterans organizing pneumonia (BOOP) ++

Lymphoid interstitial pneumonia (LIP) ±

Diffuse alveolar damage (DAD) ±

Complications of PM/DM: aspiration pneumonia secondary to +++

pharyngeal and esophageal disorder and hypostatic pneumonia and respiratory failure secondary to respiratory muscle dysfunction and hypoventilation

Pleural disease

Pleural disease ±

Spontaneous pneumothorax ±

Miscellaneous

Weakness of respiratory muscles +++

Malignancy (primary or metastatic) +

Pulmonary hypertension +

Diffuse alveolar hemorrhage ±

+++, common; ++, fairly frequent; +, occasional; ±, rare. Figure 22.2. Chest radiograph in a patient with PM/DM shows coarse reticulomicro-

nodular and alveolar pattern.

Polymyositis/Dermatomyositis and the Lung 127

Bibliography

1. Douglas WW, Tazelaar HD, Hartman TE, Hartman RP, Decker PA, Schroeder DR, Ryu JH. Polymyositis- dermatomyositis-associated interstitial lung disease. Am Rev Respir Crit Care Med 2001;164:1182–1185.

2. Fathi M, Dastmalchi M, Rasmussen E, Lundberg IE, Torling G. Interstitial lung disease, a common mani- festation of newly diagnosed polymyositis and dermatomyositis. Ann Rheum Dis 2004;63:297–301.

3. Schnabel A, Hellmich B, Gross WL. Interstitial lung disease in polymyositis and dermatomyositis. Curr Rheumatol Rep 2005;7:99–105.

4. Dalakos MC, Hohlfeld R. Polymyosistis and dermatomyosistis. Lancet 2003;362:971–982.

Figure 22.3. HRCT scan shows bibasilar and peripheral thickening of the interlobular septa, ground-glass pattern and consolidation of asymmetric distribution with pleural fibrosis.

Figure 22.4. Antibody directed against Jo-1. Fine granules condensed around the

nucleus, which diminish toward the periphery of the cytoplasm (HEp-2 cells; Euroimmun,

Lubeck, Germany; objective ×40).