Eosinophilic Granulomatosis With Polyangiitis (Churg-Strauss Syndrome)

Excerpt

Eosinophilic granulomatosis with polyangiitis (EGPA), previously known as Churg-Strauss syndrome, is a specific variant within a group of diseases characterized by necrotizing vasculitis of small- and medium-sized systemic blood vessels. This is one of the antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV), alongside granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). EGPA is distinguished from the other AAVs by its association with asthma, rhinosinusitis, and peripheral eosinophilia.

History

Jacob Churg and Lotte Strauss first described EGPA in 1951, based on autopsy findings from a case series of 13 patients. All the patients exhibited a similar pattern of severe asthma, fever, blood eosinophilia, and autopsy evidence of granulomatous necrotizing vasculitis. They named the condition allergic granulomatosis and angiitis. Their classic definition and diagnosis of the disease required the presence of the following 3 key features:

1. Eosinophilic infiltration

2. Necrotizing vasculitis of small- and medium-sized vessels

3. Extravascular granuloma formation

However, because individuals often presented with varying combinations of these features, and rarely all 3, more clinically relevant diagnostic criteria were later developed.

Lanham et al proposed a definition based on slightly different characteristics, as mentioned below:

1. Bronchial asthma

2. Blood eosinophilia of more than 1500 eosinophils per mL

3. Vasculitis involving at least 2 extrapulmonary organs

An unintended drawback of these diagnostic criteria was that they often led to delayed diagnosis, as they required the involvement of 2 or more organ systems. This delay in diagnosis was unfavorable because early treatment can prevent complications.

In 1990, the American College of Rheumatology (ACR) proposed new classification criteria for EGPA, which require the presence of 4 out of 6 features, as listed below, for diagnosis. These criteria demonstrated a specificity of 99.7% and a sensitivity of 85% for diagnosis.

1. Asthma

2. Migratory infiltrates in the lung

3. Paranasal sinus abnormalities

4. Mono- or polyneuropathy

5. Peripheral blood eosinophilia (>10% of total leukocyte count)

6. Eosinophilic tissue infiltrates in the biopsy

At the Chapel Hill Consensus Conference in 1994, EGPA was defined as "eosinophil-rich and granulomatous inflammation involving the respiratory tract and necrotizing vasculitis affecting small- to medium-sized vessels, associated with asthma and eosinophilia." This definition was significant because it excluded biopsy as a necessity for diagnosis, facilitating the early recognition of cases characterized solely by asthma and eosinophilia in tissue or blood. In current clinical practice, the 2022 ACR and European Alliance of Associations for Rheumatology classification criteria for EGPA are used. These criteria should be used when a diagnosis of small to medium vasculitis has been made and mimicking diagnoses have been ruled out.

Clinical criteria

1. Obstructive airway disease: +3

2. Nasal polyps: +3

3. Mononeuritis multiplex: +1

Laboratory criteria

1. Blood eosinophilia count >1x10(9)/L: +5

2. Extravascular eosinophilic-predominant inflammation on biopsy: +2

3. positive test for cytoplasmic antineutrophilic antibodies (cANCA): -3

4. Hematuria: -1

Sum the scores for 7 items if present. A score of greater than 6 is required for the classification of EGPA.