From Guillain–Barré–Like Neuropathy to <scp>EGPA</scp> : <scp>ANCA</scp> Testing and Kidney Biopsy as Diagnostic Turning Points

ABSTRACT Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare ANCA‐associated small‐vessel vasculitis that may involve the peripheral nervous system. Although peripheral neuropathy is a common manifestation, acute symmetric presentations may mimic Guillain–Barré syndrome (GBS), creating significant diagnostic challenges. We describe the case of a 71‐year‐old woman with a history of allergic asthma and hypertension who developed progressive distal paraesthesias and ascending weakness following a flu‐like prodrome. Neurological examination showed symmetrical flaccid weakness and generalised areflexia. Cerebrospinal fluid analysis was normal, while nerve conduction studies demonstrated acute axonal polyneuropathy fulfilling the Brighton criteria for GBS. Intravenous immunoglobulin therapy (2 g/kg) initially resulted in transient clinical improvement, but neurological symptoms rapidly relapsed with painful lower‐limb weakness. Subsequent investigations revealed acute kidney injury associated with proteinuria, microscopic haematuria and marked eosinophilia (30%). ANCA testing demonstrated strong MPO‐ANCA positivity (&gt; 134 U/mL). Kidney biopsy showed crescentic glomerulonephritis with eosinophilic interstitial infiltrates, supporting the diagnosis of EGPA‐associated vasculitis. Treatment with corticosteroids followed by rituximab led to progressive neurological and renal recovery. This case highlights that EGPA may rarely present with a GBS‐like phenotype and underscores the importance of considering vasculitic etiologies in patients with atypical or relapsing GBS presentations, particularly in the presence of eosinophilia or renal involvement. Given its favourable cost–benefit profile, ANCA testing may represent a valuable diagnostic tool in selected patients with suspected GBS to facilitate early diagnosis and timely initiation of immunosuppressive therapy.