CSF studies were negative. Extensive infectious/inflammatory laboratory and serological workup, including markers of vasculitis, paraneoplastic antibodies, and tumor markers, was unrevealing. Angiotensin-converting enzyme (ACE) level was also within normal limits. A CT scan of the chest, abdomen, and pelvis was within normal limits.

The patient's symptoms continued to worsen over the course of two months, with prominent ataxia and headaches. Given the clinical symptoms in combination with the striking and characteristic MRI findings, a diagnosis of CLIPPERS (chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids) was entertained and the patient was started on an empiric course of prednisone 60 mg qdaily. The patient's symptoms markedly improved within two days of starting prednisone, and subsequent CSF studies remained negative. A brain biopsy was deferred given the risk of morbidity, and the patient was continued on a slow steroid taper and started on methotrexate qweekly. The patient's symptoms completely resolved within two weeks.

A follow-up MRI nearly 10 months after the initial study demonstrated persistent abnormal midbrain and pontine T2/FLAIR signal, although complete resolution of associated postgadolinium enhancement. Diagnosis: CLIPPERS.