We present an IgG4-RD case of isolated cerebrovascular involvement as an initial presentation with atypical imaging and normal serum IgG4 levels. 

IgG4-RD is a multisystemic fibroinflammatory disorder. It commonly affects males in their 50s-70s. Isolated neurological involvement is rare and variable. Frequent manifestations include hypertrophic pachymeningitis, hypophysitis and orbital pseudotumor. Biopsy showing IgG4-positive plasmacytic infiltration, storiform fibrosis and obliterative phlebitis, is diagnostic. IgG4-RD is steroid-responsive. Refractory cases benefit from B-cell depleting immunosuppressants.

A 29-year-old male presented with 2 months of progressively worsening left-sided retro-orbital headaches, left-sided near-total hearing loss and painful horizontal diplopia on left gaze, preceded by gastroenteritis without systemic symptoms. Exam revealed anisocoria (L>R) with reactive pupils, left-sided esotropia with partial abducens palsy, and decreased left-sided hearing. CTA head revealed bony destruction of left petrous apex and cavernous sinus, thrombosis of left transverse, sigmoid and cavernous sinus and proximal internal jugular vein and left ICA encasement by a mass. MRI brain showed skull base meningioma with intracranial extension and extension into proximal left carotid space with involvement of the left hypoglossal and jugular foramen and left cavernous sinus. Workup demonstrated mildly elevated inflammatory markers and CSF protein, with negative CSF cytology/cytometry and hypercoagulability panel. Serum IgG levels were significantly elevated, but IgG4 levels were surprisingly normal. Systemic disease was ruled out with negative FDG-PET scan and CT thorax/abdomen/pelvis. Brain biopsy showed mixed inflammatory processes containing lymphocytes, histiocytes, and IgG4-positive plasmacytes. Patient responded well to anticoagulation, steroids and rituximab. He remained in clinical and radiologic remission at 1-year follow-up. 

This case adds to the evolving literature on IgG4-RD-related neurologic presentations. Isolated vasculopathies in young patients without risk factors should raise suspicion for rheumatological etiologies, especially IgG4-RD, even with normal serum IgG4 levels, which if diagnosed time-sensitively remains a completely treatable condition with excellent prognosis.