The disease usually progresses through three sequential phases, which are sometimes difficult to distinguish separately. The first phase is a prodromal period with many years of allergic rhinitis, nasal polyposis, and asthma. The second, eosinophilic phase is marked with blood eosinophilia and eosinophilic infiltration of different organs, including the lung (eosinophilic pneumonitis), skin (eosinophilic cellulitis), heart (infiltrative cardiomyopathy), and GI tract (eosinophilic enteritis). The third phase is the most disabling and life-threatening with necrotizing, granulomatous, multisystem, small- to medium-sized vasculitis. The disease manifestations usually start in adolescence and progress over 10 to 20 years, with vasculitis usually seen in the third and fourth decades.