Disability insurance is one of the more comprehensive types of coverage one can obtain. It is very important to fully understand each of the provisions included in your Disability policy.
An "exclusion" is one of the easier but more important things to understand. Exclusions are amendments or provisions attached to a disability insurance contract that removes a specific medical condition, type of condition, or body part from being covered. Exclusions can only be used when an applicant has a pre-existing condition that has been diagnosed, monitored, discussed, treated or noted by a medical professional.
Insurance companies use exclusions for two reasons. The first is to protect themselves from a high-risk claim in the future and the second is to allow applicants to obtain coverage, who otherwise would not qualify medically. Attaching an exclusion to a policy is the only way an insurance company can offer coverage to those who have existing conditions, without charging extremely high premiums. Although some disagree and see it as a way for insurance companies to make higher profit, it is simply the only fair way for an insurance company to offer coverage.
There are infinite things that can cause a person to become disabled. Having a couple of exclusions on your policy does not mean that it is not useful. Insurance is used to protect us from the unknown. Generally people who purchase Disability insurance do not plan on using it and those who have used it never imagined that they would. Being offered a competitively priced, comprehensive policy with a few exclusions is much better than not being offered anything at all.
Quite simply, if you are applying for individual Disability insurance and you have existing medical conditions, you should expect that they will be noted and likely excluded by the insurance company. Insurance companies perform extensive medical underwriting on disability applications and even if you "forget" to claim something on your application, it is likely that they will find out about it. The best thing to do is set realistic expectations and understand that although you may have one condition excluded, you will still be covered for the infinite number of other things that could cause you to be disabled.