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INTRODUCTION

Pulmonary vasculitis syndromes are a heterogeneous group of primary or secondary diseases. They are characterized by inflammation in the pulmonary vessels that may lead to progressive destruction of the pulmonary microvasculature. Primary or idiopathic pulmonary vasculitis is extremely rare in children; in most cases, pulmonary vasculitis is seen in the context of a systemic vasculitis syndrome. The systemic inflammatory diseases with the highest likelihood of pulmonary involvement are juvenile systemic lupus erythematosus, systemic sclerosis, juvenile dermatomyositis, and mixed connective tissue disease. The primary systemic vasculitides most commonly associated with pulmonary involvement are granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, and microscopic polyangiitis (MPA). In addition, a new autoinflammatory disease has been described recently that is associated with gain-of-function mutations in the TMEM173 gene encoding the stimulator of interferon genes (STING) referred to as STING-associated vasculopathy with onset in infancy (SAVI). SAVI is characterized by severe pulmonary vasculitic involvement. This chapter reviews the diseases associated with pulmonary involvement and discusses common clinical presentation features, diagnostic workup, and recommended therapies.

EPIDEMIOLOGY

The annual incidence of primary vasculitis in children is estimated at approximately 12 to 53 per 100,000. Primary vasculitis accounts for approximately 2% to 10% of all pediatric conditions evaluated in pediatric rheumatology clinics. Pulmonary involvement of primary or secondary vasculitides is a rare occurrence in children, and the incidence differs depending on the underlying disease.

Worldwide epidemiologic data are lacking, but Asians appear to have a disproportionately high incidence of specific types of vasculitis. Females are affected more commonly by connective tissue diseases, whereas the male-to-female ratio differs in other types of pulmonary vasculitis syndromes. Age of presentation is also variable depending on the underlying disease.

PATHOPHYSIOLOGY

The vasculitic syndromes differ not only in clinical and pathologic presentations, but also in their presumed pathogenesis. The large-vessel vasculitides are thought to be caused by cell-mediated immune reactions to poorly defined antigens. Immune complexes are involved in some of the small-vessel vasculitides. The ethnic differences in prevalence suggest that genetics and environment also may play important roles in disease susceptibility and pathogenesis. Other theories of pathogenesis include humoral factors such as anti-neutrophil cytoplasmic antibody (ANCA)–associated vasculitides. Abnormal regulation of immune complex formation may be contributory, as in Henoch-Schönlein purpura. Impaired lymphocyte regulation, specifically T-regulatory cell dysfunction, also may be involved. In many reports, infections have been implicated in many of the vasculitides including Henoch-Schönlein purpura, granulomatosis with polyangiitis, and polyarteritis nodosa. Higher frequencies of exposure to parvovirus B19 and cytomegalovirus have been reported in children with polyarteritis nodosa, whereas there is growing evidence that microbial agents also play a role in the induction of primary systemic vasculitis.

CLINICAL MANIFESTATIONS AND DIFFERENTIAL DIAGNOSIS

The clinical and pathologic features of pulmonary vasculitis syndromes vary according to the type and size of blood vessels affected and the underlying disease process. Despite ...

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