EGPA and steroids

Q: What is the caveat in interpreting peripheral blood eosinophilia in patients with suspected Eosinophilic granulomatosis with polyangiitis (EGPA or Churg-Strauss syndrome)?

Answer: Glucocorticoids

EGPA is a vasculitis of the small and medium-sized arteries, described 75 years ago by Churg and Strauss. Common symptoms are asthma, nasal and sinus symptoms, and peripheral neuropathy. It can involve many body organs and progress slowly, and it is usually diagnosed in the fifth decade of life. As it gets worse, the patient develops pulmonary opacities, cardiomyopathy, renal insufficiency, and gastrointestinal (GI) symptoms. 

Peripheral blood eosinophilia is the most characteristic finding with absolute blood eosinophil counts ≥1000 cells/microL (or greater than 10 percent of the total leukocyte count). This blood workup finding should raise suspicion for EGPA. 

Many patients have been administered glucocorticoids to control their chronic symptoms from EGPA. Glucocorticoids may reduce or fluctuate eosinophil counts and falsely rule out EGPA. 

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References:

1. CHURG J, STRAUSS L. Allergic granulomatosis, allergic angiitis, and periarteritis nodosa. Am J Pathol 1951; 27:277.

2. Cottin V, Bel E, Bottero P, et al. Revisiting the systemic vasculitis in eosinophilic granulomatosis with polyangiitis (Churg-Strauss): A study of 157 patients by the Groupe d'Etudes et de Recherche sur les Maladies Orphelines Pulmonaires and the European Respiratory Society Taskforce on eosinophilic granulomatosis with polyangiitis (Churg-Strauss). Autoimmun Rev 2017; 16:1.

3. Grayson PC, Ponte C, Suppiah R, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology Classification Criteria for Eosinophilic Granulomatosis with Polyangiitis. Ann Rheum Dis 2022; 81:309.