Eosinophilia in Rheumatology: A Management Challenge

Eosinophils are an important and mediate several key functions; however, they can be associated with a number of different disorders and organ dysfunction. Eosinophilia is defined as counts above 0.5–1.5×109/L, and persistent counts above 1.5×109/L are classed as hypereosinophilia. Although several systemic diseases and single-organ diseases manifest with eosinophilia, it is not always pathological. In some, eosinophilia is a key marker of disease activity, and in others, it is a reaction to another immune trigger, making it crucial to making the right diagnosis. These include helminthic and parasitic infections; immunological disorders; haemato-oncological disorders, such as hypereosinophilic syndrome; rheumatological disorders, such as eosinophilic granulomatosis with polyangiitis; and organ-specific disorders, such as asthma (respiratory) and eosinophilic oesophagitis (gastrointestinal). A systematic approach to eosinophilia is essential to make a prompt diagnosis and institute appropriate management. This article discusses the approach to a patient presenting with eosinophilia, the diagnostic work up, and management considerations. The authors particularly focus on some of the rheumatological conditions that can give rise to significant eosinophilia, and how to differentiate between these.