SpineTF12-Post Vaccinial Myelitis

Clinical Profile:

H/O dog bite 1 month back. Patient received ARV (anti rabies vaccine). Patient developed backache with urinary retention and weakness in BLE a day prior to the scan.

Findings:

There is e/o a hyperintense signal on the T2 Weighted images in the cervico-dorsal spinal cord, centrally, over about the C5 to D11 vertebral levels. This lesion appears hypointense to normal cord signal on the T1 Weighted images. Slight increase in the diameter of the cervico-dorsal spinal cord over these levels is noted. Screening, FLAIR axial images of the brain reveal a focal hyperintense signal in the periventricular white matter in the right temporo-occipital region.

Discussion: 

Myelitis or ADEM (Acute Disseminated Encephalomyelitis) can occur following vaccination against rabies, measles, small pox, polio and rarely after tetanus antitoxin. Patients usually present with back pain and urinary hesitancy that progresses to paralysis. They usually undergo moderate to complete recovery.

ADEM is an immune-mediated disease. It is characterized by early destruction of myelin due to structural homology between the brain tissue and myelin proteins and the brain-derived tissue in ARV. The incidence of ADEM following neural anti-rabies vaccine is 1/300 to 1/7000. The reactions are less, when less than 7 injections are taken, whereas they are more after 14 injections. Pathologically, ADEM is characterized by perivenous inflammation and demyelination in the CNS. Antibodies cross-react with brain tissue to give perivenous inflammation, multifocal meningeal infiltration, demyelinating foci and destruction of nervous tissue. ADEM is classically differentiated from multiple sclerosis (MS) by the intensity of inflammation.  The highest density of cells is at the edge of the perivenous lesions in MS whereas it is at the center of the lesion in ADEM.

On MRI there is usually swelling of the cord with a hyperintense signal on the T2W images (transverse myelitis type of picture). In 60% of cases, the lesions may enhance. Plaque like lesions mimicking multiple sclerosis may be seen. In the brain, there is usually involvement of the white matter (whereas there is predominant involvement of the grey matter in rabies encephalitis). On the basis of imaging alone, it may not be possible to differentiate from post infectious myelitis, cord ischemia, cord tumors or multiple sclerosis