Is hypertrophic pachymeningitis a dural lesion of IgG4-related systemic disease?

Both multifocal fibrosclerosis and hypertrophic pachymeningitis are rare disorders of unknown etiology, characterised by chronic inflammation leading to dense fibrosis. There have been several reports of multifocal fibrosclerosis with hypertrophic pachymeningitis. Autoimmune pancreatitis is frequently associated with various extrapancreatic lesions, their pathological similarities such as dense inflammatory fibrosis with lymphoplasmacytic infiltration strongly suggests a close relationship between autoimmune pancreatitis and multifocal fibrosclerosis. Recently, autoimmune pancreatitis including these systemic fibrosing disorders may be classified as IgG4-related systemic disease. However, the relationship between HP and IgG4-related systemic disease is still uncertain. We performed immunohistochemical examinations in autopsy specimens from a patients with HP. Histological findings can be summarized as follows: sever interstitial fibrosis and diffuse inflammatory cells infiltration, presenting nonspecific inflammatory changes. Immunohistochemically, diffuse infiltrates in the dura consisted predominantly of UCHL-1 positive T or L-26 positive B lymphocytes. Many IgG4 positive plasma cells were also infiltrated. To our knowledge, this may be the first report which showed IgG4 positive plasma cells infiltration in the dura in a patient with HP. It is postulated that HP may be a dural lesion of IgG4-related systemic disease.