Report a case of immunoglobulin 4-related disease (IgG4-RD) presenting as a cerebral mass with leptomeningeal enhancement.

IgG4-RD is an immune-mediated disorder of unknown cause. It is frequently under-recognized and delayed treatment results in extensive fibrosis. Our case highlights the importance of identifying IgG4-RD as a cause of neurological problems as early diagnosis leads to better outcomes. 

A 42-year-old man with a history of hypertension and atrial fibrillation came for evaluation of left brain mass manifested by five month history of progressive right hemiparesis, right hemisensory loss and focal motor seizure with secondary generalization.

Initial magnetic resonance imaging (MRI) of the brain at symptom onset revealed a three centimeter intra-axial left posterior parietal lobe mass with vasogenic edema. Repeat brain MRI four months later showed extensive left parietal vasogenic edema with abnormal leptomeningeal and dura enhancement in the left frontoparietal and occipital regions. Cerebrospinal fluid (CSF) analysis revealed an elevated Immunoglobulin G (IGG) index at 1.21 but otherwise was unremarkable. Computed tomography (CT) chest, abdomen, and pelvis with contrast and positron emission tomography (PET) scan were negative for malignancy. IgG subtype panel was sent which revealed a high IgG4 level (98 mg, normal value 2-96 mg/dl) and high IgG4/IgG ratio (15%, normal value 5%). Biopsy showed chronic inflammatory infiltrate composed predominantly of plasma cells and eosinophils with focal granulomatous features involving the leptomeninges and overlying dura as well as increased IgG4 plasma cells per HPF(>50) with an increased IgG4/IgG ratio. Prednisone 60 mg daily was started, and one month later patient had improvement of hemiparesis, mass size, leptomeningeal enhancement, and edema.

Although uncommon, brain parenchymal involvement and leptomeningeal enhancement is a possible manifestation of IgG4-RD.