Churg-Strauss syndrome is a rare disease in which the immune system attacks small and medium-sized blood vessels throughout the body. It affects roughly 1.2 people per million each year worldwide, and about 15 per million are living with it at any given time. The condition is now formally called eosinophilic granulomatosis with polyangiitis, or EGPA, though many doctors and patients still use the older name. It involves a combination of severe asthma, high levels of a specific white blood cell called eosinophils, and widespread blood vessel inflammation that can damage the heart, nerves, lungs, kidneys, and skin.
Why the Name Changed
The disease was originally named after Jacob Churg and Lotte Strauss, the pathologists who first described it in 1951. At the 1994 Chapel Hill Consensus Conference, an international group of experts redefined it as inflammation rich in eosinophils and granulomas (clusters of immune cells) that targets the respiratory tract and blood vessels, occurring alongside asthma and elevated eosinophil counts. The name was updated to eosinophilic granulomatosis with polyangiitis to describe what the disease actually does rather than who discovered it. EGPA belongs to a broader family of conditions called ANCA-associated vasculitis, named for the antibodies found in some patients’ blood.
The Three Stages
EGPA typically progresses through three overlapping phases, though not everyone experiences all of them and the stages don’t always follow a strict order.
The first is the allergic stage. This can last for years before anyone suspects a deeper problem. It looks like adult-onset asthma that keeps getting worse, along with nasal allergies, nasal polyps, and repeated sinus infections. Many people are treated for asthma alone during this period.
Next comes the eosinophilic stage. Eosinophils, white blood cells normally involved in fighting parasites and mediating allergic reactions, multiply far beyond normal levels and begin accumulating in tissues. This buildup damages organs directly. Lung symptoms like coughing and wheezing intensify, and digestive problems appear: stomach pain, nausea, vomiting, and sometimes gastrointestinal bleeding.
The third is the vasculitic stage, where inflammation spreads to the walls of blood vessels themselves. Narrowed or damaged vessels reduce blood flow to organs, and this is when the most serious complications develop. The heart, kidneys, skin, and peripheral nerves are all vulnerable.
How It Affects the Body
Nerve damage is one of the most common and disruptive features. A pattern called mononeuritis multiplex, where individual nerves in different parts of the body fail one by one, occurs in roughly 78% of patients. This can cause sudden weakness or numbness in a hand or foot, often in an asymmetric pattern that distinguishes it from more common nerve conditions. Cranial nerve involvement is far less frequent, showing up in only about 4% of cases.
Cardiac involvement varies widely across different patient populations, with reported rates ranging from about 17% to over 90% depending on how it’s measured and how thoroughly it’s screened for. Heart muscle disease (cardiomyopathy) is particularly concerning because it’s linked to worse outcomes. Kidney damage, gastrointestinal complications, and skin changes like purplish spots or nodules round out the picture. Not every patient develops all of these, but the potential for multi-organ involvement is what makes EGPA serious.
Diagnosis
There is no single test that confirms EGPA. Diagnosis relies on a combination of clinical features, blood work, and sometimes tissue biopsy. The 2022 classification criteria from the American College of Rheumatology and the European Alliance of Associations for Rheumatology use a point system. Features that earn points toward a diagnosis include obstructive airway disease (+3 points), nasal polyps (+3), blood eosinophil counts above a specific threshold (+5), eosinophil-dominant inflammation seen on biopsy (+2), and mononeuritis multiplex (+1). A combined score of 6 or higher supports classification as EGPA.
Interestingly, testing positive for certain antibodies (specifically cytoplasmic ANCA or anti-proteinase 3 antibodies) actually subtracts points, because those markers are more characteristic of related but distinct forms of vasculitis. ANCA antibodies are detectable in only 30 to 40% of EGPA patients, and when present, they’re usually the MPO-ANCA type. This means the majority of people with EGPA are ANCA-negative, which has implications for how the disease behaves and how it’s treated.
Treatment
Oral corticosteroids remain the foundation of EGPA treatment. They suppress the overactive immune response and bring eosinophil levels down. Most patients start on high doses, which are then tapered gradually over months.
What gets added alongside steroids depends on disease severity. For severe cases involving the heart, kidneys, nerves, or gastrointestinal tract, stronger immune-suppressing medications are used as first-line therapy alongside steroids. These work by broadly dampening the immune system to halt the vasculitis before it causes irreversible organ damage.
For patients with active but non-severe disease, a targeted therapy called mepolizumab is now recommended alongside steroids. Mepolizumab works by blocking a specific signaling molecule that drives eosinophil production and survival. It was approved by the FDA for EGPA after a major clinical trial (the MIRRA trial) showed that 32% of patients on the drug achieved complete response, meaning no detectable disease activity and a steroid dose reduced to near-zero levels. A subsequent European study of over 200 patients found similar complete response rates of about 30% at 12 months and 36% at 24 months. The drug is given as a subcutaneous injection every four weeks.
The distinction between patients whose disease is primarily driven by eosinophils versus those with a more vasculitis-dominant pattern matters for treatment selection. Eosinophil-driven disease tends to respond better to targeted therapies like mepolizumab, while vasculitis-dominant disease may respond better to broader immunosuppression.
Outlook and Prognosis
Prognosis depends heavily on which organs are affected. Doctors use a tool called the Five-Factor Score to estimate survival risk. It assigns one point each for five findings: significant kidney dysfunction, high levels of protein in the urine, central nervous system involvement, cardiomyopathy, and severe gastrointestinal complications like bleeding or tissue death. The score maps directly to five-year survival: 88% for a score of zero, 74% for a score of one, and 54% for a score of two or higher.
These numbers come from older data, and outcomes have improved with newer treatments. But the pattern holds: patients whose disease is limited to asthma, sinus problems, and elevated eosinophils generally do well long-term, while those with heart or kidney involvement face a tougher course. Most people with EGPA require some form of ongoing treatment for years, and flares can occur when medications are reduced. The goal of long-term management is keeping the disease in remission while minimizing the side effects of steroids and other immune-suppressing drugs.