Introduction Persistent eosinophilia can be caused by a variety of diseases best illustrated by the a acronym NAACCP (neoplasm, Addison's, allergic/asthma, collagen vascular diseases, cholesterol emboli and Parasites) or CHINA (connective tissue disease, helminths, idiopathic hypereosinophilic syndromes, neoplasia and allergies). In practice the level of blood eosinophil count can be used to identify the most likely aetiology. A raised eosinophil count from any cause will cause end organ damage by release of eosinophilic granules. To illustrate this key learning point we describe a gentleman who had been investigated in the past for arthralgia.

Case Presentation A 65-year-old gentleman who was referred to neurology after developing a common peroneal nerve palsy. His initial investigations were aimed at looking for compressive causes. During his inpatient admission he developed respiratory failure and ischaemic bowel and required transfer to the intensive care unit. He was eventually diagnosed with cANCA positive vasculitis confirmed on bowel biopsy. Following diagnosis he was given high-dose steroids. He is now being treated with monthly cyclophosphamide infusions. He has residual neuropathic pain, ulnar and common peroneal neuropathy, however his systemic illness is now quiescent.

Conclusion Early recognition of raised eosinophils in the context of systemic symptoms would prevent significant morbidity and possible fatalities. We should also consider early nerve biopsy.