Simultaneous new onset of neuromyelitis optica spectrum disorder in identical twins

OBJECTIVE: To present a case of two identical twins presenting concurrently with symptoms and subsequent initial diagnosis of neuromyelitis optica spectrum disorder (NMOSD). METHODS: Clinical, laboratory and MRI findings for both twins were reviewed and presented here. RESULTS: Twin A presented with right eye pain and subsequent blurred vision in right eye. MRI of the brain and spine demonstrated pre-chiasmal right optic nerve enhancement and T2 hyperintense lesions in the spinal cord at T7 and T9 levels. Cerebrospinal fluid (CSF) analysis was remarkable for NMO/aquaporin-4 (AQP4) fluorescence-activated cell sorting (FACS) titre of 1:32 and a serum NMO/AQP4-IgG positive titre of 1:10 000. Twin B presented with diplopia. MRI of the brain and spine demonstrated T2 hyperintense lesions in the periventricular cerebral white matter, in the periaqueductal white matter of the pons, in the midbrain and the cervical spinal cord. Neurological examination findings revealed incomplete right trochlear palsy, rotatory nystagmus, an incomplete left internuclear ophthalmoplegia and hyper-reflexia. CSF analysis was remarkable for NMO/AQP4 FACS titre of 1:256 and a serum NMO-IgG positive titre of 1:10 000. Both twins responded well to intravenous steroid therapy. There was no adverse environmental exposure present. CONCLUSION: We present an interesting and rare case of identical twins presenting concurrently and for the first time with NMOSD.