Mononeuritis Multiplex as a Diagnostic Challenge in Eosinophilic Granulomatosis With Polyangiitis: Implications of Early Versus Delayed Recognition

A 63-year-old female patient presented to the acute medical unit with what appeared to be a case of progressive mobility decline, a common and often nonspecific presentation in acute medicine. She described upper and lower limb weakness and numbness affecting her ability to walk. Originally, her upper limb numbness was treated as ulnar nerve compression in the community. She also had multiple episodes of shortness of breath throughout the year, which were initially managed in the community as suspected asthma exacerbations; however, her symptoms were non-specific. Routine investigations revealed severe eosinophilia (13.37 × 10⁹/L), anaemia, and leucocytosis. Neurophysiology confirmed mononeuritis multiplex, and further autoimmune testing revealed positive anti-neutrophil cytoplasmic antibodies (P-ANCA) and elevated myeloperoxidase (MPO) antibodies. This was ultimately diagnosed as eosinophilic granulomatosis with polyangiitis (EGPA), a rare presentation that challenged initial diagnostic assumptions. This case is an example of how not all presentations of EGPA are straightforward and how it might be missed in an acute medical setting. Through this case report, we wanted to emphasise the subtle and often vague nature of mononeuritis multiplex in EGPA. We would also like to highlight the implications of a delayed diagnosis on patients with EGPA and how this affects the long-term health of patients. Lastly, we would like to discuss newer treatments with anti-interleukin-5 (IL-5) target drugs, which are used to reduce relapse rates in the disease.