Eosinophilic granulomatosis with polyangiitis (NORD)

Eosinophilic granulomatosis with polyangiitis, or EGPA, previously known as Churg-Strauss syndrome, is a rare immune disorder that causes systemic organ damage from eosinophilic involvement and inflammation of small blood vessels, called vasculitis. It is frequently associated with allergic manifestations like asthma, rhinitis, and sinusitis. 

EGPA is characterized by the presence of increased amounts of eosinophils in the blood. Eosinophils are a type of white blood cell that play a role in the body’s response to allergens and parasitic infections. It’s unclear how EGPA develops, but it’s thought that some kind of trigger— such as an infection, medication, or environmental allergen— sets off an exaggerated eosinophilic immune response that causes damage to tissues and organs. Some people may be more susceptible to developing EGPA. When not treated, EGPA leads to the development of granulomas, which are collections of immune cells that cluster together to wall off an area of inflammation.  

Signs and symptoms of EGPA can vary greatly from one individual to another, but there are typically three phases: prodromal, eosinophilic, and vasculitic, although they don’t always occur in that order. The prodromal phase is characterized by adult-onset asthma and rhinitis that are often attributed to allergies. Unlike asthma, EGPA often has progressive lung involvement, commonly with infiltrates. In addition, chronic inflammation of the nasal lining causes growth of tissue within the nasal cavity called polyps. These polyps contain large amounts of eosinophils, and can block the sinus tracts, preventing mucus from draining out of the sinuses and causing congestion or inability to smell. 

The eosinophilic phase results in infiltration of eosinophils into organs and can cause characteristic lesions called eosinophilic granulomas. When eosinophils infiltrate the lungs, pulmonary infiltrates can form that are seen on radiologic imaging. Eosinophils can also affect the heart lining and muscle, and cause heart damage, which, in severe cases, can result in heart failure. In some patients, clots can form in the blood vessels or in the heart. There may also be gastrointestinal, or GI, symptoms, including abdominal pain; diarrhea as a result of eosinophils in the lining of the stomach or small bowel; and more rarely, blood in the stool due to inflammation of the GI tract. Other organs can also be affected such as the kidneys, especially in patients with an autoimmune type of EGPA who have an antibody called ANCA that is present in the blood.  

The most severe presentation of EGPA is the vasculitic phase, when vasculitis occurs. During this phase of the disease, a necrotizing vasculitis that affects smaller vessels supplying peripheral nerves occurs. Clinically, this manifests as nerve pain and loss of sensation and/or muscle strength, which in some patients can lead to loss of muscle control of the foot or wrist.