Central nervous system Aquaporin4 autoimmunity revealed by a single pseudotumoral encephalic lesion

The radiological spectrum of neuromyelitis optica has become broader since the detection of aquaporin4 antibodies. We report a case of neuromyelitis optica patient with pseudotumoral encephalic lesion. A 66 year-old woman presented with sudden left lateral homonymous hemianopsia. A brain MRI showed an isolated and extensive right temporo-parieto-occipital lesion, involving periventricular white matter and the corpus callosum, with strong enhancement on post-gadolinium T1 weighted images, highly suggestive of lymphoma. Spinal cord MRI and body CT scan were unremarkable. Lumbar puncture showed pleocytosis, raised total protein level without abnormal cells or oligoclonal bands. A brain biopsy demonstrated non-specific demyelination. Serum aquaporin4 antibodies were positive, which was consistent with the diagnosis of neuromyelitis optica. Cases of central nervous system aquaporin4 autoimmunity presenting with an isolated brain lesion without optic neuritis or myelitis are extremely rare: this is the second case so far and the first one with advanced magnetic resonance characterization. Pseudotumoral encephalic lesions should include a large differential diagnosis, and testing aquaporin4 antibodies must be considered in order to avoid brain biopsy.