rosy71- I've lost count how often he's had it. These were the main ones:
The first time was at about 2-3 weeks. A large red mark about 1" long on his arm. The Gp thought he'd been accidently knocked by one of his sisters. I suspect he thought dd2 had bitten him, although he nicely didn't say so, because i was in a bite sort of shape. I know she hadn't btw.
2nd time he came out in what looked like about 1cm in diameter bruises all over his legs. He was about 10 weeks old. You could watch them coming out but slowly. Luckily I was with dd1's friends, one parent was a GP and she diagnosed him and arranged for bloods to be taken straight away. He was very alert and cheerful so you could see he was fine.
Similar happened at about 12 and 14 weeks.
I think at about 15 months he came out in tiny pin prick spots starting on his forehead and spreading rapidly to the rest of his body. The only time we've really been dashed to hospital because he had an ear infection and was unwell, plus the speed they were coming out was alarming.
In between, and since, when he's unwell there's a very good chance that he will have several pin prick red spots. They're typically on his ear, temple and forehead, but occasionally spreads further. If it gets below his head, or becomes very extensive then they usually want to do bloods, otherwise it's just something that he does when unwell.
It's obviously something he has a tendancy to.