The API for Revit parameter description property has been missing for many years. The fact applies to all parameter kinds such as project parameters, family parameters, and the new guy global parameters. It is still missing in the latest Revit API.
Due to the limitation, it is not possible to retrieve the descriptions of these parameters from Revit by its API in any addins, including ours such as the Revit Parameter Organizer. Worse, there is no workaround at all about it through our investigation. So, the simplest task has became the most complex one. What a shame!
Another odd thing is that some way is provided to set parameter descriptions such as for family parameters through the FamilyManager.SetDescription() method, but that is useless from the Revit addin perspective as users will not have any chance to check the existing parameter descriptions before deciding to change them or maintain them. Ouch!
Though with limitations like such, we have tried our best to make our software as flexible, reliable and powerful as possible.