Low-dose rituximab for MPO-ANCA-associated hypertrophic pachymeningitis with delayed onset of renal involvement: a case report.

Hypertrophic pachymeningitis (HP) is a rare disorder characterized by focal or diffuse inflammatory thickening of the dura mater. Patients may present with prolonged localized central nervous system involvement and often lack the typical manifestations of ANCA-associated vasculitis (AAV), making diagnosis and treatment challenging. We report the case of a 55-year-old woman who presented with recurrent headache, right eye pain, and visual decline. Laboratory testing showed positivity for myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA), and brain magnetic resonance imaging (MRI) demonstrated extensive dural thickening and enhancement involving the bilateral cerebral convexities, falx cerebri, and cerebellar tentorium. Based on the clinical, laboratory, and imaging findings, she was diagnosed with MPO-ANCA-associated hypertrophic pachymeningitis. During follow-up, the patient experienced multiple relapses and showed poor tolerance to several immunosuppressive agents. She was subsequently treated with low-dose rituximab (100 mg) for induction and maintenance therapy. After treatment, her clinical symptoms improved, and the dural thickening and enhancement on imaging were alleviated. During follow-up, she developed proteinuria and hematuria, and renal biopsy ultimately confirmed microscopic polyangiitis (MPA). After intensified treatment, inflammatory markers and renal involvement were brought under control. This case suggests that, in patients with recurrent MPO-ANCA-associated hypertrophic pachymeningitis who are intolerant to multiple immunosuppressive agents, an individualized low-dose rituximab regimen may help achieve a period of clinical and radiological remission.