I have a friend with a puppy around 5 months old. It is a medium to large breed.
They say it has been intermitently lame for a few weeks. X rays have showed nothing. It's on anti inflammatories but is lame if they are stopped. Sometime just one limb (varies) sometimes all limbs. The vet has no suggestions.
My first thought was Lyme's disease but does anyone have any thoughts?

You can name the breed as it may be relevant

Pano? Ocd?

Zuma was a bit older but sounds very much like when he had Pano. He had xrays on all legs which were sent to referral vet for diagnosis. Completely cleared on its own

Have you seen the threads about canine phsyios and mctimmons practitioners on here it might be worth having one of them look at your dog

Sounds like Panosteitis (sp), surprised this isn't what the Vet has suggested, often called wandering lameness, growing pains.

Most often seen in fast growing young dogs, more often males.

It is an inflammation of the of the long bones, and they grow out of it.  Pain killers and rest is the usual treatment.
https://www.petmd.com/dog/conditions/musculoskeletal/c_multi_panosteitis

My first thought was Pano

Sounds like we are all of a similar mind. Strange the vet didn't suggest this it's not that uncommon

I went STRAIGHT to Panosteitis.    It's maybe a touch young for this, but not for nothing has this been called the creeping disease.   It affects the long bone, rotates round all the limbs, and is clearly darned painful for the dog.    Normally it's treated with aspirin, buffered aspirin.   The good news is eventually the patient will recover.  There has to be crate rest, obviously.    I'd have thought vets know about this these days and so going to Hip or Elbow dysplacia can be avoided.  

The breeder needs to be told - there is an indication that this is hereditary.   She may already have had puppies with this but if this does prove to be Pano, that breeding should be avoided.

Mine is a breed that has lines that suffer with this.