Abstract
A man in his early 70s with a 4-year history of diffuse large B cell lymphoma (DLBCL) was admitted to our hospital with diplopia and achromatopsia. Neurological examination revealed visual impairment, ocular motility disorder and diplopia on looking to the left. Blood and cerebrospinal fluid investigations showed no significant findings. MRI revealed diffusely thickened dura mater and contrast-enhanced structures in the left apical orbit, consistent with hypertrophic pachymeningitis (HP). We performed an open dural biopsy to distinguish the diagnosis from lymphoma. The pathological diagnosis was idiopathic HP, and DLBCL recurrence was ruled out. Following methylprednisolone pulse and oral prednisolone therapy, his neurological abnormalities gradually receded. Open dural biopsy played an important role not only in diagnosing idiopathic HP but also in relieving the pressure on the optic nerve.