Idiopathic hypertrophic pachymeningitis: an autoimmune IgG4-related disease.

Hypertrophic pachymeningitis (HP) is a rare disorder that causes thickening of the dura mater. Inflammatory lesions may be located in the cerebral or spinal dura mater or, less frequently, in both locations simultaneously. Numerous clinico-pathological entities cause thickening of the pachymeninges. Indeed, HP is a potential manifestation of many different diseases, but the diagnosis often remains uncertain. Cases in which the pachymeningitis has no known aetiology are termed "idiopathic" HP (IHP). Recently, it has been suggested that IgG4-related disease represents a subset of cases previously diagnosed as idiopathic hypertrophic pachymeningitis. Little is known regarding the pathogenic events of IHP. In a general theory, the inflammatory infiltrate, mainly consisting of B and T lymphocytes, activates fibroblasts and induces collagen deposition, leading to tissue hypertrophy and increased dural thickness. Clinical manifestations of IHP depend upon the location of the inflammatory lesions and compression of the adjacent nervous structures. Three central pathological features are lymphoplasmacytic infiltration, obliterative phlebitis, and storiform fibrosis. MRI is the examination of choice for the preliminary diagnosis of IHP. Histopathological examination of a biopsy specimen of the dura mater would finally confirm the diagnosis. The differential diagnosis for HP is broad and includes infections, autoimmune disorders, and neoplasia. Currently, there is no consensus about treatment for patients with IHP. There is a preference for glucocorticoid treatment on diagnosis followed by the addition of other immunosuppressive agents in the event of a recurrence. Rituximab is used in patients who did not respond to glucocorticoids or to conventional steroid-sparing agents.