Differentiation between Idiopathic Acute Transverse Myelitis and Myelopathic Multiple Sclerosis by MRI

ABSTRACT

BACKGROUND: Idiopathic acute transverse myelitis (ATM) is an inflammatory or demyelinating illness of unknown etiology. It is usually monophasic, though recurrences at the same spinal level of the initial attack have been reported. In Korea, the spinal cord is the most commonly affected site of multiple sclerosis (MS) and its clinical features often resemble those of ATM. As the prognoses of these two conditions are different, it is important to distinguish them from each other. The purpose of this study was to evaluate spinal MRI findings that could help differentiate ATM from myelopathic MS. METHODS: A total of 50 MRIs obtained less than four weeks after the onset of symptoms in 13 patients with ATM and 24 patients with clinically definite MS were reviewed retrospectively. The diagnostic criterion for ATM was a rapid onset of spinal motor and sensory dysfunction referable to a distinct spinal cord level with sphincter dysfunction, reaching its peak within 4 weeks, in the absence of pre-existing neurological diseases and spinal cord compression. For MS, Poser's criteria were used. We analyzed the lesion length, location, cross-sectional area, cord morphology, and contrast enhancement patterns in each of the groups. RESULTS: Characteristic MRI findings of ATM included; 1) centrally located hyperintensity (86%) occupying more than half of the cross-sectional area of the cord (100%), 2) thoracic preponderance in lesion location (thoracic 7, cervicothoracic3, cervical 1), 3) lesion length of more than 3 vertebral segments (100%), 4) cord swelling (73%), and 5) focal or diffuse enhancement (90%). Most MRI findings of myelopathic MS (MMS) were not different from those of ATM, especially in Asian-type MS. Different MRI features of MMS from those of ATM included 1) peripherally located hyperintensity occupying less than half of the cross-sectional area of the cord (20.8%), 2) lesion length less than two vertebral segments (33.3%), 3) normal cord morphology (25%), 4) no enhancement (36.1%), and 5) multifocality (22.2%), which were more commonly found in Western-type MS. CONCLUSIONS: Although there were some differences of spinal MRI features between ATM and MMS, it was not easy to differentiate them by MRI findings alone. The findings suggest that Asian-type MS has unique MRI characteristics similar to those of ATM and different from those of Western-type MS.