Evaluation and Differential Diagnosis of Hypereosinophilia in Rheumatology Practice

Abstract

<b><i>Background:</i></b> There has been no investigation so far on the prevalence or causes of hypereosinophilia during rheumatic diseases. <b><i>Objectives:</i></b> The study aimed to identify the prevalence and causes of hypereosinophilia among the patients followed in a rheumatology department. <b><i>Methods:</i></b> The patients aged 18 years or over followed in our rheumatology department between January 2010 and December 2019 who had at least one AEC ≥1,500/µL measurement in their peripheral blood count were identified retrospectively. <b><i>Results:</i></b> Over the 10 years, a total of 130,769 peripheral blood counts were performed, of which 3.9% showed eosinophilia and 0.065% showed hypereosinophilia. Hypereosinophilia was identified in 85 patients. The underlying rheumatic disease was determined in 89.4% (<i>n</i> = 76) of patients. Of these, the most frequent one was rheumatoid arthritis at a ratio of 40.8%, followed by eosinophilic granulomatosis with polyangiitis (EGPA) at a ratio of 10.5%. Hypereosinophilia was in primary form in 3.5% of the patients, whereas secondary to another condition in 91.8% (<i>n</i> = 78) of the cases and idiopathic in 4.7% (<i>n</i> = 4) of patients. The most common cause of secondary hypereosinophilia was drug induced, as detected in 61.2%, followed by allergic conditions in 11.5% and EGPA in 9.4%. In 15.2% (<i>n</i> = 13) of the cases, hypereosinophilia was associated with an underlying rheumatic disease. In the cases with drug-induced hypereosinophilia, most often (in 28.8%) methotrexate was the offending agent. <b><i>Conclusions:</i></b> Rheumatologists should be cognizant that hypereosinophilia concurrent to rheumatic diseases is usually not due to the underlying rheumatic disease, except for the conventional eosinophil-related rheumatic diseases.