We very much appreciate the interest in our recent publication regarding ‘False positive aquaporin-4 IgG leading to misdiagnosis of neuromyelitis optica spectrum disorder in patient with spinal arteriovenous fistula’. We agree that the case presented by Brooks et al.1 was similar to ours in terms of clinical presentation and imaging findings except that their case was a spinal dural arteriovenous fistula whereas ours was a filium terminale arteriovenous fistula (which is much rarer). In both conditions the pathomechanism of the abnormal extensive longitudinal T2 hyperintense lesion in the spinal cord was venous congestive edema, formerly referred to as Foix-Alajouanine syndrome; however, the use of that term is now discouraged as it is not a diagnosis per se, but rather the sequelae of a vascular shunting lesion overwhelming the venous outflow of the cord.

We agree that abnormal perimedullary flow voids on MRI are an important sign to raise the possibility of spinal vascular lesions that require spinal digital subtraction angiography for definitive diagnosis. These cases highlight the importance of ruling out alternative diagnoses in the evaluation of patients with suspected neuromyelitis optica spectrum disorder.

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