The choice of who and when to disclose to is a huge one. If you put it in as a search in the magnifying glass in the upper left you will get a lot of good hits. It will be impacted on your career type and just where you are on your career path. I chose not to disclose (I'm an accounting systems analyst and have been a consultant at times) as I did not want to be passed over for challenging assignments or work. My symptoms (primarily balance and gait) could easily be explained as due to something else so it wasn't an issue. Over time, however, I started working for a boss that started making unreasonable demands and I could simply not make her happy. For example once she insisted that I drive in to the office during blizzard conditions when the law enforcement had ordered our roads closed. We had 3' drifts the crews couldn't keep clear and on a good day I had a 45 minute commute. That is just one example. In my work I could easily (and did) work remote very easily and put in a lot of overtime from home working with people in other time zones (my job required I worked with people from all over the world). As I did not disclose when she made moves to remove me from her team I had no defense as I had not disclosed. In hind sight I should have at least disclosed to HR and had some protection. The laws are different in every country and probably applied differently by different companies in the various industries. You certainly wouldn't be required to disclose, most likely, but consider your co-workers advice carefully but I totally understand your concerns as well as they were much like my own. As many people without obvious symptoms don't disclose and the impact of DMDs on slowing progression is just starting to play out over time when people think of who they know that has MS it is usually someone with major disability. By not disclosing we are likely doing ourselves an injustice but until there is a major campaign or enough celebrity types out there with MS as good role models we have a perception problem.

@murray - quite why it is the concern of a colleague escapes me. I didn't disclose it for many years as it wasn't really affecting me. When I did once I was inexplicably ended with being made redundant. I sued them and won. I had a good lawyer. These days the Equality Act protects you, in theory. However, there are many ways an employer who can read and has half a brain can ensure they aren't able to be deemed liable. It is your judgement. A large employer is probably a safer bet as they are geared up for these things. They have HR departments, access to legal advice etc. Once you have been employed for more than a year your rights are cemented and you are harder to mess about. If you get a whiff of unfair treatment then I would strongly urge you to go to a specialist lawyer sooner rather than later. There are many legal charities that also specialise in disability law.