New condition

For PIP it's not so much about the diagnosis, but how your son is affected in his daily life.
Particularly around the PIP activities and descriptors.

If the new diagnosis doesn't change the PIP components for his current award and the group he is currently in I'd be careful about how you notify the DWP (and indeed if you need to notify them).
What PIP award does he get?
There have been cases when notifying a worsening in circumstances have prompted an early PIP reassessment and the withdraw of the award.

If the current PIP award remains relevant, then if you are going to notify the DWP I'd be inclined to post them confirmation of the diagnosis. Include a note that you have sent this solely to update their records, and are not seeking to have the award looked at again.

See https://forums.moneysavingexpert.com/showthread.php?t=5868217#1

Liz484 wrote: »

I understand what you're saying but in a couple of years time when he's reassessed wont they ask why we never told them when he was first diagnosed.

No. As has been said PIP isn’t about a diagnosis. If you rang them to report this then he will be sent more forms and he risks losing what he already has.

Liz484 wrote: »

They have started him on medication straight away. Would we get into trouble if they did find out and we never told them.

If a PIP claimant 's health improves to the extent that they can reliably perform the PIP activities without the need for an aid / assistance, and therefore their award is now no longer applicable - then they are under a duty to notify the DWP.

When their condition worsens (or a new condition develops), and they believe their abilities have further reduced, more help is needed and they now meet the PIP descriptors for a higher award (i.e from Standard to Enhanced) - then they can tell the DWP of that change in circumstances and the DWP will reassess the claimant to see if the higher award should apply.

When their condition worsens (or a new condition develops), and they continue meet the PIP descriptors for their current award (e.g. Enhanced DL), then (IMO) the claimant doesn't need to tell the DWP as the PIP descriptions still apply and the reasons for the current award have not changed. There are no change of circumstances in the application of the PIP award.
Claimants need to be very careful about notifying changes - the DWP may take such a notification as a supersession request; and will then reassess the claimant with the risk of a flawed assessment and a reduced award.

You don't seem to have grasped that the PIP award does not depend on diagnosis.
A claimant doesn't get a PIP award because they have arthritis.
(Or COP / anxiety / epilepsy / etc)
They may get a PIP award because this condition so severe enough that they cannot reliably perform the PIP activities without an aid or assistance.
https://www.benefitsandwork.co.uk/personal-independence-payment-pip/pip-points-system

Going back to epilepsy - if this is controlled by medication then no points would be awarded.The DWP assessment assumes appropriate medication is taken. It looks at the impact of the condition on daily life, not the condition by itself.

You have had some good advice, by posters with experience of the benefits system. But, your responses seem to show that you are reluctant to accept what you have been told.
Please re-read the posts carefully, before notifying PIP.