The Thickening Dilemma: A Rare Case of Idiopathic Hypertrophic Pachymeningitis Mimicking Granulomatosis With Polyangiitis.

Idiopathic hypertrophic pachymeningitis (IHP) is a rare, chronic inflammatory disorder characterized by fibrotic thickening of the dura mater. The etiology of IHP is currently unknown; however, IHP often mimics other inflammatory conditions (causes of secondary hypertrophic pachymeningitis) including neurosarcoidosis, granulomatosis with polyangiitis (GPA), and IgG4-related disease. IHP manifests clinically with a spectrum of neurologic symptoms, including headache, paresthesia, cranial nerve (CN) palsies, and seizures.