Eosinophilic Granulomatosis with Polyangiitis Following Central Diabetes Insipidus: A Rare Case Report

Introduction: Eosinophilic granulomatosis with polyangiitis (EGPA) is a systemic vasculitis often preceded by asthma or allergic rhinitis. Although its symptoms overlap with other ANCA-associated vasculitides, central diabetes insipidus (CDI) is rarely reported in EGPA. CDI may arise from various conditions, including other vasculitides such as granulomatosis with polyangiitis (GPA). Here, we present a rare case of EGPA with preexisting CDI and severe kidney impairment, which improved with multidisciplinary treatment. Case Description: A 68-year-old woman with asthma and eosinophilic sinusitis was diagnosed with CDI 17 months prior to admission, based on hypotonic urine, low AVP response, and loss of posterior pituitary signal on MRI, with no structural abnormalities or hormonal deficiencies. She later developed general malaise, weight loss, elevated creatinine (5.21 mg/dL), eosinophilia, and MPO-ANCA positivity. Kidney biopsy revealed eosinophil-rich necrotizing vasculitis with crescents. EGPA was diagnosed and treated with steroids, rituximab, and plasma exchange. Kidney function improved without dialysis. Follow-up MRI showed slight signal return in the posterior pituitary. A repeat hypertonic saline test showed mild improvement in AVP secretion. Discussion: This case highlights a rare occurrence of EGPA developing after CDI, suggesting a possible pathophysiological link. While EGPA is known for multiorgan involvement, posterior pituitary dysfunction is extremely uncommon. Among reported cases of EGPA with CDI, clinical courses varied, but all showed improvement with immunosuppressive therapy. In our case, slight recovery of posterior pituitary MRI signal and AVP secretion was observed after treatment. Although the precise mechanism remains unclear, the absence of eosinophilia and pituitary enlargement at CDI onset, along with the subsequent response to immunosuppression, suggests that vasculitic ischemia, rather than eosinophilic infiltration, may have contributed to CDI. A direct pathological link could not be confirmed, and idiopathic CDI cannot be excluded; however, the clinical course raises the possibility that CDI may reflect early central involvement of EGPA. Clinicians should suspect EGPA when CDI occurs in patients with asthma or sinusitis, as this may indicate early vasculitic involvement.