Eosinophilic granulomatosis with polyangiitis (EGPA), also known as Churg-Strauss syndrome, is a systemic vasculitis that typically involves the lungs.¹ The eponym “Churg-Strauss syndrome” stems from a publication of Jacob Churg and Lotte Strauss in 1951, in which they described 13 patients with pulmonary “periarteritis nodosa,” allergic symptoms, peripheral eosinophilia, and eosinophilic vasculitis.² The term “Churg-Strauss syndrome” was not applied to the disease until the 1970s.^3,4 In 1985, Andrew Churg clarified the distinction between EGPA and granulomatosis with polyangiitis (GPA) also known as Wegener granulomatosis, two systemic vasculitic syndromes with a granulomatous component, from other granulomatous diseases of the lung such as bronchocentric granulomatosis, lymphomatoid granulomatosis, and necrotizing sarcoidosis.⁵ Another term that has been used for Churg-Strauss syndrome is “allergic granulomatosis and angiitis.”^4,6,7 The current International Chapel Hill Consensus Conference nomenclature refers to Churg-Strauss syndrome as EGPA, in part because the allergic nature of the disease has been questioned, and for “symmetry” with GPA and microscopic polyangiitis (MPA).⁸ Since 30% to 40% of patients with EGPA have antineutrophilic cytoplasmic antibodies (ANCA), it is classified with GPA and MPA as one of the ANCA-associated vasculitides.⁸ In the ACR/CHCC (American College of Rheumatology/Chapel Hill Consensus Conference), EGPA is defined as “Eosinophil-rich and necrotizing granulomatous inflammation often involving the respiratory tract, and necrotizing vasculitis predominantly affecting small to medium vessels, and associated with asthma and eosinophilia. ANCA is more frequent when glomerulonephritis is present.”⁸ This description is “nosologic” or definitional, not to be used for diagnostic criteria.⁸

The classic theory asserts that EGPA is an allergic reaction with an exaggerated tissue response resulting in tissue destruction mediated by destructive enzymes within eosinophil granules.^7,9 There may be a genetic component predisposing to the disease, as there has been a reported association with HLA-DRB4 haplotype. Eosinophils show in vitro abnormalities, and humoral immunity is also abnormal, as demonstrated by prominent IgG4 and IgE responses.⁹

Many triggers may be involved in the initial onset of disease, including infection, drugs, and vaccinations.¹ Several reports have documented the progression of asthma to EGPA after leukotriene receptor antagonist treatment,¹⁰ which may represent unmasking of the disease or a reaction to the therapy.

EGPA is one of the less common vasculitides, and as such a rare disease. Its prevalence ranges from 10.7 to 13 cases per million inhabitants, with an annual incidence of 0.5 to 6.8.^1,9

As with other vasculitic syndromes, a diagnosis rests on clinical and pathologic findings. A clinical definition without pathologic confirmation includes asthma, blood eosinophilia exceeding 1,500/mm³, and clinical features suggestive of vasculitis involving two or more organs.¹¹ However, asthma may follow and not precede the vasculitic phase; eosinophilia may fluctuate and disappear, especially after treatment with corticosteroids; and the clinical manifestations of vasculitis are nonspecific without biopsy confirmation.¹

The pulmonary manifestations of EGPA include cough, exertional dyspnea, hemoptysis, and chest pain.¹² The division of clinical symptoms into stages (allergic, eosinophilic, and vasculitis) is largely of historic interest as there is no uniform progression of these manifestations.¹³

Extrapulmonary involvement with EGPA is most common in the peripheral nerves and musculoskeletal system, followed by gastrointestinal tract, skin, kidney, central nervous system, and heart. Thrombotic episodes are not uncommon.¹⁴ Multiorgan involvement is typical.¹⁵

Heart involvement,¹⁶ followed by kidney and lungs,¹⁷ may lead to life-threatening events.