IgG4-Related Disease Manifested as Hypertrophic Pachymeningitis: A Case Report and Literature Review.

Background: IgG4-related hypertrophic pachymeningitis (IgG4-RHP) is an extremely rare central nervous system (CNS) autoimmune disorder, characterized by dural thickening, space-occupying effects, and neurological compression symptoms. It is frequently misdiagnosed as meningioma due to overlapping radiological features, leading to inappropriate management. This study aims to report a unique case of IgG4-RHP with skull destruction and subcutaneous mass formation, and summarize its diagnostic and therapeutic strategies through literature review. Methods: A 53-year-old male with a chronic subdural hematoma history was admitted for a progressive right frontal subcutaneous mass. Preoperative computed tomography (CT) and magnetic resonance imaging (MRI) were performed, followed by staged surgeries (subcutaneous biopsy and craniotomy with subtotal resection). Histopathological examinations (Hematoxylin and Eosin staining, IgG/IgG4 immunostaining) and serum IgG4 detection were conducted. The patient received postoperative prednisone acetate (60 mg/d) and 3-month follow-up. A literature search was also performed to analyze 34 previously reported IgG4-RHP cases. Results: Histopathology showed dense lymphoplasmacytic infiltration, storiform fibrosis, ≈40 IgG4+ plasma cells per high-power field (HPF), and an IgG4+/IgG+ ratio of ≈30%. Serum IgG4 was significantly elevated to 1521 μg/mL (normal < 1350 μg/mL), with marked reduction in residual lesions on follow-up MRI. Literature review revealed a 73.5% male predominance, mean age of 48.6 years, headache as the most common symptom (58.8%), and a 38.5% misdiagnosis rate. Glucocorticoids alone or combined with immunosuppressants achieved favorable outcomes in 96.0% of treated cases. Conclusions: Histopathological examination combined with serum IgG4 detection is the gold standard for IgG4-RHP diagnosis. Surgical resection relieves mass-occupying effects, while glucocorticoids are first-line therapy. Long-term follow-up is necessary for recurrence monitoring, and rituximab is effective for refractory cases. Awareness of atypical manifestations like skull destruction can reduce misdiagnosis and improve outcomes.