Researchers studying the brains of patients who had multiple sclerosis (MS) have found a new “subtype” of the disease that does not damage the so-called white matter of the brain.

Results were published in August in The Lancet Neurology.

Cerebral white matter is made up of myelinated nerve fibers that connect portions of the brain and spinal cord and serve to communicate with other parts of the body. The demyelination of this white matter has been thought to cause nerve cell degeneration in patients with MS.

Researchers at Cleveland Clinic in Ohio studied brains and spinal cords from patients who had MS when they died. In all, researchers examined brains and spinal cords from 100 deceased patients between May 1998 and November 2012.

Though all patients had been diagnosed with MS, not all of the tissues examined showed loss of myelin — the protein that protects nerve fibers — in white matter.

Researchers’ findings suggest there’s a “subtype” of MS, which they refer to as myelocortical multiple sclerosis. This subtype results in demyelination of the spinal cord and cerebral cortex, but not of the cerebral white matter. Cortical neuronal loss, the researchers said, “can be an independent pathological event in myelocortical MS. Compared with control brains, cortical neuronal loss was greater in myelocortical MS cortex than in typical MS cortex.”

Of the 100 brains studied, 12 of them did not show white matter demyelination, though those 12 did show the loss of neurons seen in MS.