A 58-year-old man with recurrent rhinosinusitis and nasal polyps developed new-onset asthma poorly responsive to inhaled bronchodilators. He responded well to oral corticosteroids but developed exacerbations each time steroids were tapered. Two years later, he developed weakness and paraesthesias in his right arm and leg that progressed to right wrist and foot drop.

Electromyography confirmed mononeuritis multiplex. Laboratory studies were pertinent for leucocytosis with predominant eosinophilia (48%), elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), a positive myeloperoxidase (MPO) antibody, and perinuclear antineutrophil cytoplasmic antibody (p-ANCA) pattern (Figure 80-1) on immunofluorescence study. A purpuric rash (Figure 80-2) over the left ankle revealed leukocytoclastic vasculitis (Figure 80-3) with eosinophils on histopathology. A diagnosis of Churg-Strauss syndrome (CSS) was made. He was treated with high-dose steroids and oral cyclophosphamide with resolution of eosinophilia and remarkable clinical improvement by 6 months. He was subsequently switched to azathioprine for maintenance of remission.

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  Rare, multisystem, autoimmune disorder

  
  
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  First described by Churg and Strauss in 1951

  
  
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  Classified as a vasculitis and characterized by inflammation of small- to medium-sized arteries, arterioles, and venules in association with allergic syndromes like asthma, rhinitis, and sinusitis

  
  
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  Mean age at onset 38 to 54 years¹

  
  
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  Rare, but more severe in children and adolescents

  
  
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  Slight male predominance¹

  
  
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  Prevalence: 10.7 to 14 per 1 million adults; incidence: 0.11 to 2.66 per 1 million adults per year¹

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  Exact pathogenesis is not well understood.

  
  
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  Autoimmunity is suggested by the presence of hypergammaglo-bulinemia, increased levels of immunoglobulin E (IgE), ANCA, and rheumatoid factor (RF) in some patients.¹

  
  
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  Human leukocyte antigen (HLA)-DRB4 is the main genetic risk factor and may increase the risk of developing vasculitic manifestations.¹

  
  
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  Polymorphisms in interleukin (IL)-10 gene have been associated with CSS.²

  
  
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  CD4- CD25- T-regulatory cells (Tregs) that produce IL-10 are diminished in CSS patients with asthma or eosinophilia but not in CSS patients in remission.²

  
  
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  The prominence of allergic features suggests a heightened T helper 2 (Th2) immunity, and pulmonary angiocentric granulomatosis suggests heightened Th1 immunity.²

  
  
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  Abnormal eosinophil function is likely as a result of increased eosinophil recruitment by Th2 cytokines (IL-4 and 5) and decreased eosinophil apoptosis.²

  
  
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  Association of CSS with use of leukotriene receptor antagonists (eg, montelukast) in steroid-dependent asthma has been reported but causality has not been proven.^2,3

  
  
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  Rare reports of cases associated with cocaine and omalizumab (anti-IgE monoclonal antibody) use.^1,2