Hi Mac
The award is based on his condition at the time. If he was having problems, but it wasn't yet diagnosed, you could put in for a Mandatory Reconsideration and add this information if you think it would lead to an increased mobility award. (This is within a month of the decision letter).
If it is something that is going to deteriorate you could wait and monitor what happens and then put in for a change of circumstances informing them of this newly diagnosed issue and how it impacts the care needed. Be aware it will immediately trigger a reassessment of the claim.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
