Relevance of clinical findings for diagnosis of neuromyelitis optica in MRI and NMO‐IgG era

Sir, Spinal MRI abnormalities and detection of specific serum autoantibodies (NMOIgG) [1] are central amongst the new criteria for diagnosis of neuromyelitis optica (NMO) [2]. Despite the consistency of these paraclinical tools, the here reported case emphasizes how clinical findings are still important in the diagnostic process. A 41-year-old woman had sudden visual loss in the right eye. After intravenous methylprednisolone (IVMP) visual function became normal. Seven months later, she complained of symptoms suggestive for myelitis (motor and sensory impairment with cervical level) and sudden visual loss in the left eye. Brain and whole spinal MRI (1.5 Tesla), as well as complete CSF examination, were normal. Seven months later, brain and spinal MRI performed with the same technique and evaluated by two experienced neuroradiologists (B.S. and P.A.), were still normal. During the subsequent 2 years, she had three episodes of myelitis and five episodes of visual loss involving both eyes. Brain MRI and CSF examination were still normal. Spinal MRI was normal again (Fig. 1a), but it was abnormal for the first time 5 months later (3 years after clinical onset), showing a longitudinal lesion at C3-C5 level (Fig. 1b), with gadolinium enhancement. NMO-IgGs were not detected when indirect immunofluorescence was performed according to the original protocol [1]. Two months after, she had sensory loss and motor weakness in the right arm. Brain MRI was normal. NMOIgGs were negative again. Spinal MRI showed an extensive swelling lesion of the cord at C3-C7 level, with gadolinium enhancement. Table 1 summarizes the clinical and paraclinical findings. Concerning therapy, she was treated with chronic oral prednisone and received IVMP after each relapse, with incomplete recovery. Our case focuses on clinical history in spite of the relevance of spinal MRI and NMO-IgG for NMO diagnosis. This patient showed a clinical evolution characterized by recurrent optic neuritis and myelitis, without extra-optic-spinal symptoms, just 1 year after clinical onset. According to the old Wingerchuk s criteria [3], this suggested a relapsing NMO. However, according to the revised criteria [2], as NMO-consistent spinal MRI ensued only 3 years after clinical onset and NMO-IgGs were repeatedly negative, NMO would not be diagnosed at this stage. We are aware that the revised NMO diagnostic criteria, which have demonstrated good sensitivity and specificity [2], cannot cover every single NMO case, and that there are exceptions. Moreover, our case with his peculiar course adds a new element to the clinico-radiological dissociation paradox. This paradox is usually described as the absence of clinical signs despite MRI abnormalities [4] but, in the present case, clinical symptoms and neurological signs widely preceded the detection of MRI abnormalities. This has never been reported in NMO, although we described a similar clinico-neuroimaging dissociation in a multiple sclerosis case [5]. The occurrence of symptoms suggesting myelitis could be because of the delay before MRI scans. Anyway, in our case, MRIs were performed both close to and distant to myelopathic symptoms. A possible reason for failure to demonstrate MRI cord lesions is that damage could be because of axonal degeneration in presence of normal-appearing white matter [6]. Our findings remind that the weight of clinical evidence should be never underestimated even in the MRI and IgG-NMO era.