History A 53-year-old man experienced headache and double vision that progressed over 1 year. After a traumatic fall, he was hospitalized, and proptosis was identified at physical examination. Laboratory tests were remarkable for leukocytosis. Hematocrit level, thyroid stimulating hormone level, autoimmune antibody level, erythrocyte sedimentation rate, and C-reactive protein level were normal. Computed tomography (CT) of the head revealed bilateral intraconal masses, for which magnetic resonance (MR) imaging of the orbits was subsequently performed ( Fig 1 ). CT imaging of the chest and abdomen ( Fig 2 ) revealed periaortic and retroperitoneal stranding. Perinephric biopsy was performed, and a diagnosis of immunoglobulin G4 (IgG4)-related disease was made based on identification of a few plasma cells per high-power field that were positive for IgG4. Orbital biopsy was then performed, but the results were inconclusive for IgG4-related disease. The patient was discharged and given steroid therapy for presumed IgG4-related disease. [Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text][Figure: see text] Several months later, the patient returned to our institution with progressive symptoms despite ongoing steroid treatment. His case was reviewed by several specialists to develop alternative treatments for IgG4-related disease. After review of the available images, a neuroradiology fellow (M.D.M.) performed history taking and a physical examination and subsequently recommended radiography of the lower extremities ( Fig 3 ). [Figure: see text][Figure: see text].