Churg-Strauss syndrome overview

# Overview
Eosinophilic granulomatosis with polyangiitis previously called Churg-Strauss syndrome is a small and medium-sized necrotizing vasculitis, with extravascular granuloma formation. The disease was first described by Churg and Strauss in 1951. The etiology is not known. However, various environmental factors, allergens, genetics, and drugs may play a role in triggering disease process by activating eosinophils, B and T lymphocytes and macrophages. The disease is characterized by the presence of asthma, peripheral eosinophilia, rhinosinusitis, peripheral neuropathy and multiple organ involvements including skin, GI tract, and kidney.

# Historical Perspective
Two pathologists Churg and Strauss first described the disease in 1951. They named it as allergic granulomatosis with angiitis. Over the years, they called the disease by the name of Churg-Strauss syndrome. In 2010, American College of Rheumatology changed this name to eosinophilic granulomatosis with polyangiitis based on histopathology.

# Classification
Revised International Chapel Hill Consensus Conference 2012 on nomenclature of vasculitides, defines eosinophilic granulomatosis with polyangiitis (formerly known as Churg - Strauss syndrome) as an eosinophilic, granulomatous inflammatory disease affecting most commonly the conducting pulmonary airways, and leading to a necrosis of the small and/or medium-sized vessels. Eosinophilic granulomatosis with polyangiitis is often synonymous with adult-onset asthma. According to revised CHCC 2012, eosinophilic granulomatosis with polyangiitis is considered as a variant of the ANCA - associated vasculitis.

# Pathophysiology
Eosinophilic granulomatosis with polyangiitis is a medium and small vessel vasculitis, leading to necrosis. The pathogenesis of eosinophilic granulomatosis with polyangiitis is not fully understood. Eosinophilic granulomatosis with polyangiitis occurs as a  result of a complex interaction involving genetic and environmental factors that lead to an inflammatory response involving eosinophils, lymphocytes. Autoimmunity has an evident role in the presence of ANCA, hypergammaglobulinemia, elevated levels of immunoglobulin E, and rheumatic factor in the pathogenesis. HLA-DRB4 is correlated with increased risk of development of vascular manifestations of the Churg-Strauss syndrome. On microscopic pathology, eosinophilic infiltration, necrotizing granulomatous vasculitis and necrosis of small and medium-sized arteries can be seen.

# Causes
The etiology of eosinophilic granulomatosis with polyangiitis is not known. Various allergens, infections, vaccinations and drugs may be responsible for developing disease through an allergic or autoimmune response. Genetics may play a role includes, HLA -DRB4 and IL-10 gene polymorphisms are associated with the development of eosinophilic granulomatosis with polyangiitis.

# Differentiating Churg-Strauss syndrome from Other Diseases
Eosinophilic granulomatosis with polyangiitis must be differentiated from other diseases that can cause eosinophilia, purpura, alveolar hemorrhage, necrotizing extra-capillary glomerulonephritis, such as granulomatosis with polyangiitis and microscopic polyangiitis.

# Epidemiology and Demographics
The incidence of Eosinophilic granulomatosis with polyangiitis range from 2.5 to 16.6 per 100,000 individuals. Prevalence ranges from 2 to 16 per 100,000 individuals. Mean age at diagnosis of eosinophilic granulomatosis with polyangiitis around 45-50 years. In general, eosinophilic granulomatosis with polyangiitis affects men and women equally.

# Risk Factors
There are no established risk factors for eosinophilic granulomatosis with polyangiitis. However, certain environmental agents including various allergens, infections, desensitization, vaccination and genetics may act as triggering agents. Those triggers may be responsible for the inflammatory response with eosinophils and lymphocytes.

# Natural History, Complications and Prognosis
Eosinophilic granulomatosis with polyangiitis develops through three phases, include prodromal phase, eosinophilic phase, vasculitic phase. Most complications result from the vasculitic phase. Most common complications include cardiomyopathy, myocardial infarction, perimyocarditis, rapidly progressive renal failure, GI bleeding, neuropathy and status asthmaticus. Prognosis of eosinophilic granulomatosis with polyangiitis is poor if left untreated. Prognosis is most likely dependent on stage at which the disease was diagnosed and organ involvement. The five-factor score assessment (FFS) is a good predictor of survival rate. It can be used to choose the appropriate treatment.

# Diagnosis

## History and Symptoms
Obtaining a complete history is an important aspect in making a diagnosis of eosinophilic granulomatosis with polyangiitis. As it can help differentiate between the ANCA associated vasculitis and other possible causes that may mimic the disease. Symptoms of eosinophilic granulomatosis with polyangiitis typically develops through three phases, include prodromal phase, eosinophilic phase, and vasculitis phase. Clinical presentation depends on organ system involvement. Most common symptoms include asthma, sinusitis, weakness, arthralgia, purpura, arrythmias, hematuria and peripheral neuropathy.

## Physical Examination
A comprehensive physical examination including pulmonary, ENT, neurologic, skin, abdominal and renal systems must be performed to help identify and properly diagnose eosinophilic granulomatosis with polyangiitis form other diseases. On examination, patients may show clinical manifestations of asthma (dyspnea, tachypnea), petechiae, palpable purpura, skin nodules, rhinitis, nasal polyposis, chest pain, abdominal pain, and neurologic manifestations. On auscultation, wheezing, rhonchi, friction rub, abnormal heart sounds may be found.

## Laboratory Findings
The laboratory findings in eosinophilic granulomatosis with polyangiitis  include complete blood count with differntial to evaluate abnormal eosinophilia, serologic and immunologic tests to identify antineutrophil cytoplasmic antibodies, acute phase reactants, and urinalysis to evaluate proteinuria and microscopic hematuria. Gold standard for diagnosis is biopsy of lung.

## Chest X Ray
On chest x-ray, eosinophilic granulomatosis with polyangiitis is characterized by bilateral multifocal nonsegmental consolidation, bronchial wall thickening, reticulonodular opacities, bilateral hilar adenopathy, and pleural effusion.

## CT Scan
On high-resolution computerized tomography (HRCT) scan, eosinophilic granulomatosis with polyangiitis will show airspace consolidation, ground-glass opacities, centrilobular nodules, bronchial wall thickening and/or dilatation, pleural effusions, and hilar or mediastinal lymph node enlargement.

## Ultrasound
There are no significant ultrasound findings associated with eosinophilic granulomatosis with polyangiitis.

## Other Imaging Findings
Electrocardiogram and echocardiogram, GI endoscopy, electromyelography can be used to diagnose eosinophilic granulomatosis with polyangiitis.

# Treatment

## Medical Therapy
The mainstay of management for eosinophilic granulomatosis with polyangiitis is glucocorticoids and cyclophosphamide. Immunosuppressive agents (eg, azathioprine and methotrexate) can be used for maintenance therapy. Rituximab, interferon-alpha, anti IgE antibodies and plasma exchange can be used as second-line therapy in the management of eosinophilic granulomatosis with polyangiitis.

## Surgery
Surgical intervention is not usually recommended for the management of eosinophilic granulomatosis with polyangiitis. However, myringotomy, polypectomy, and endoscopic sinus surgery may be performed in some patients to treat upper airway disease.

## Prevention
There are no established measures for the primary and secondary prevention of eosinophilic granulomatosis with polyangiitis.