Those brown patches are dead tissue. It may be from cold, overwatering, or too much sun last summer. or some combination environmental conditions. My E. grandialata did not find the conditions in an outside bed satisfactory during its first winter. It grew several inches in the Spring, Summer, and Fall of its first year outside, but succumbed to our SF Bay cold wet winter even though I covered up the whole bed during times of rain and cold.

Removing it to a pot and watching for almost a year did not produce a growth response or any pups. I finally gave up on my plant even though it was not quite dead yet. In contrast, another columnar Euphorbia (ammak) is perfectly happy here during its third winter outside.

Your plant may still be living, but there is no recovery for the unsightly damaged areas. There is significant corking at the base of both plants. It may have a very slow internal rot.

It looks like the part on the left has pupped. Remove those come spring and repot and try to find the right conditions to grow this without damage.