Researchers have described a new subtype of multiple sclerosis that features neuronal loss, but no demyelination of the brain’s white matter. The findings by Cleveland Clinic researchers support the concept that neurodegeneration and demyelination can occur independently in MS, and underscore the need for more sensitive MRI techniques for evaluating brain pathology in real time and monitoring treatment response in patients with the disease.

This new subtype of MS, called myelocortical MS (MCMS), was indistinguishable from traditional MS on MRIs. The researchers observed that in MCMS, part of the neurons become swollen and look like typical MS lesions indicative of white matter myelin loss on MRI. The disease was only diagnosed in post-mortem tissues.

In the study of brain tissue from 100 MS patients who donated their brains after death, the researchers observed that 12 brains did not have white matter demyelination. They compared microscopic tissue characteristics from the brains and spinal cords of 12 MCMS patients, 12 traditional MS patients, and also individuals without neurological disease. Although both MCMS and traditional MS patients had typical MS lesions in the spinal cord and cerebral cortex, only the latter group had MS lesions in the brain white matter. Despite having no typical MS lesions in the white matter, MCMS brains did have reduced neuronal density and cortical thickness, which are hallmarks of brain degeneration also observed in traditional MS. Contrary to previous belief, these observations show that neuronal loss can occur independently of white matter demyelination.

The study’s authors said the identification of this new MS subtype highlights the need to develop more sensitive strategies for properly diagnosing and understanding the pathology of MCMS. They are hopeful the findings will lead to new tailored treatment strategies for patients living with different forms of MS.

The findings were published in the journal Lancet Neurology.