Immunoglobulin G (IgG)₄-related disease is a rare autoimmune disorder that may be associated with hypertrophic pachymeningitis (HP). We report a case of biopsy-proven IgG4-related HP in a patient whose initial HP manifestation mimicked giant cell arteritis (GCA).

Case Presentation

 A 58-year-old man with a medical history of Factor V Leiden mutation and deep venous thrombosis presented to Rheumatology Clinic with a one-month history of intermittent fever, scalp tenderness, hip stiffness and jaw claudication. Erythrocyte sedimentation rate (ESR,108mm/Hr) was elevated. Temporal artery biopsy was initially interpreted as consistent with GCA. He was started on high-dose prednisone followed by tocilizumab (1.5 months later) with clinical improvement. However, 4 months later, he presented to the Neurology Clinic with 3 weeks of right-sided headache, diplopia, and right-hand numbness after prednisone was tapered to 30mg/day. Physical examination revealed right pupil dilation and ophthalmoplegia involving oculomotor, trochlear and abducens nerves. ESR, C-reactive protein (CRP), antinuclear antibody (ANA), antineutrophil cytoplasmic antibodies (ANCA) and serum IgG₄were unremarkable; myeloperoxidase antibody (1.9) mild positive. Brain MRI demonstrated dural enhancement in the right cavernous sinus. Spine MRI revealed multiple foci of cervical dural thickening/enhancement with cord compression at the cervicothoracic junction. Cerebrospinal fluid analysis showed 8 nucleated cells (72% lymphocytes), elevated protein (126 mg/dL) and IgG index (1.58), and positive oligoclonal bands. CSF cytology/flow cytometry showed no malignant cells. The T₁dural lesion biopsy showed lymphoplasmacytic inflammation with predominant IgG₄-positive plasma cells, storiform fibrosis and obliterative phlebitis, consistent with IgG₄-related HP. Re-review of the temporal artery biopsy revealed necrotizing vasculitis involving the vasa vasorum but no inflammation/giant cells within the temporal artery itself. Symptoms improved with high-dose methylprednisolone and he was started on rituximab. 

This case illustrates how IgG₄-related pachymeningitis can mimic GCA at initial presentation.   Detailed physical examination and pathology review is crucial in the diagnosis.