The SSA claims rep might be giving you good advice. You may, however, want to discuss your case with a Social Security attorney. Many Social Security attorneys offer free initial consultations. Most of these cases are handled on a contingency fee basis (up to 25% of back benefits, capped at $6000).
1. Countable earnings averaging more than $1000 a month (it was $980 in 2009) is considered substantial gainful activity or SGA. If you are performing SGA, SSA will generally deny your disability claim, no matter how impaired or disabled you may actually be. (Averaging close to that amount might also lead SSA to conclude you still could be able to perform work.)
2. Social Security disability claims can be paid retroactively up to 12 months. If you apply March 1, 2010 and are found to have become disabled, say, as of March 1, 2008, Social Security will pay you Social Security disability as of March 1, 2009. Waiting to see how your illness progresses may not hurt you.
3. There is a five-month waiting period for Social Security disability. This means that if SSA finds you disabled as of January 1, 2010, your disability benefits will begin as of June 1, 2010. This is one of the reasons persons apply for both Social Security and SSI. There is no waiting period for SSI. However, SSI is means-tested. If you have other income or countable resources in excess of $2000 ($3000 for a couple), you might not be eligible for SSI.
4. Social Security requires that your disability last at least 12 months or in death. MS can be tricky to adjudicate. There may be periods when you can work followed by periods when you cannot. Short periods of work (under six months) can be treated by SSA as Unsuccessful Work Attempts (UWA) and disregarded in determining whether you are disabled. The issue for SSA will be at what point did your MS stop you from being able to perform work existing in significant numbers.
Carey provides some great information to consider, but in my mnd, one important factor is missing - how long it takes to move a case through the system in PA. You can expect the process from initial application to hearing before an administrative law judge to take almost two years. It sounds like your MS is pretty serious and could lead to total disability in the near future. If you withdraw your application, you will have to start the clock all over again with a new application. This is a judgment call that should be made after consulting a social security attorney who is familiar with the hearing office in your area. Free consultations are the norm. Good luck.