It depends on the exact policy you take out. Usually PMI will exclude any pre-existing conditions and will also have general exclusions such as alcohol and/or drug abuse. There are some exceptions to this rule, however.
In some cases, for groups with a minimum of 10 members, you can have your medical history disregarded, although this is not common. More likely for inclusion is cases when there has been no reoccurrence of the condition for a few years. For example, if you’ve had problems with your back in the past – but had no issues for two years you may find this is covered by your insurer.