Many disability insurance policies have a "pre-existing condition" limitation that either bars payment of any benefits or limits payment of them to some specific time period, most often 12 months. This bar or limit applies, for instance, where the claimant's disability is "caused by," "contributed to by," or "resulting from" a pre-existing condition.
It is not at all unusual for a claimant to find themself disabled due to a number of illnesses and conditions, at least one of which may be a pre-existing condition. Does this mean that the claim will be barred or payment of benefits be limited on account of the pre-existing condition? Maybe but not necessarily.
If the claimant's disability is due to a number of factors including a pre-existing condition the key question will be whether the claimant would still be disabled even if the pre-existing condition did not exist. Courts call this a "but for"test, as in but for the pre-existing condition the claimant would not be disabled under the terms of the policy. We have a good discussion of this type of "but for" analysis regarding a case involving a disability insurance policy issued by Reliance Standard, Has Reliance Standard Denied Your Disability Insurance Benefits Claim Based on a Mental Disorder or Condition?