16th January 2024

Background

Epidemiology

Eosinophilic granulomatosis with polyangiitis (EGPA) is another type of autoimmune ANCA associated small and medium vessel vasculitis. This condition was previously known as Churg-Strauss syndrome and is the least common of the ANCA associated vasculitides referenced in the previous section. It is also classed as one of several hypereosinophilic diseases. 

It is a multi-system disease; however, the most commonly involved organ is the lung. The estimated incidence is 1-3 cases per 1 million people in the UK, but higher in the asthmatic population. Presentation typically occurs in asthmatic patients who are 40 to 60 years of age, with slightly higher incidence in patients of male sex compared to female sex. It rarely occurs in children or those older than 65 years of age. The 5-year survival rate with appropriate treatment can be up to 100% in some cases. 

Pathophysiology 

As with the other autoimmune vasculitides, the exact aetiology and pathophysiology of EGPA are unknown. It has been proposed that exposure to environmental triggers, e.g., infection, results in raised serum immunoglobulin (IgE), TH1 and TH2 cytokines (interleukin 4, 5 and 13) levels. Th2 cytokines contribute to the maturation and activation process of eosinophils, which directly release toxic proteins. These proteins drive inflammation; therefore, raised levels of eosinophils due to raised IL-5 results in higher levels of toxic protein release and, hence, more inflammation. Levels of regulatory T cells, which protect against autoimmune disease development, have been found to be lower in those with EGPA.

As with GPA, ANCA is also thought to play a role in this disease, likely via development of vessel inflammation due to neutrophil activation. Genetic factors may also be involved; for example, the interleukin (IL)10 gene and HLA class of immune cells are both associated with EGPA.

It has been suggested that omalizumab and leukotriene receptor antagonists use can reveal undiagnosed cases of EGPA if they improve asthma symptoms to the point that oral steroid weaning can occur, and clinical manifestations of EGPA then become apparent.