Evaluation and Differential Diagnosis of Hypereosinophilia in Rheumatology Practice.

BACKGROUND

There has been no investigation so far on the prevalence or causes of hypereosinophilia during rheumatic diseases.

OBJECTIVES

The study aimed to identify the prevalence and causes of hypereosinophilia among the patients followed in a rheumatology department.

METHODS

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.

RESULTS

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% (n = 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% (n = 78) of the cases and idiopathic in 4.7% (n = 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% (n = 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.

CONCLUSIONS

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.