Black Lab puppy has severe itching.

Question
Dear Dr. Gotthelf,

I have a two 5 month old lab puppies, one chocolate and one black.  The black puppy has had severe itching since we brought him home at 8 weeks.  We first suspected fleas, but never found any on either dog.  They are currently on advantix every 30 days.  At about 2 and a half months, he lost almost all his hair on the underside of his belly, and developed pyoderma.  The vet suspected demodex mange, but never found a mite after 6 skin scrapes.  He was put on an antibiotic for 14 days, and the infection cleared up, but only until the antibiotic was gone, and the itching never ceased.  At about 3 months, his belly hair grew back, but he lost almost all the hair around his eyes.  We did another 3 skins scrapes with no mites, and he was put back on another antibiotic for 4 weeks instead of 2.  The pyoderma didnt respond to this antibiotic at all, and we then switched vets.  The new vet suspected sarcoptic mange, but also found no mites after three more scrapings.  She treated him anyways with revolution, then after three days, an oral dose of ivermectin each day for about 2 weeks, another antibiotic, and malaseb shampoo, itching was a little better, but still noticable.  After a few days, the infection cleared up, but he still had the hair loss around his eyes.  At about 4 months, he was still itching severly, and again, the infection came back after the antibiotic was finished, so we switched to a hypoallergenic diet, and refilled the antibiotic.  A food by Prescription Diet, of duck and potato.  The vet also put him on prednisone for about a week.  He responded well to the prednisone and again the infection cleared up.  The hair around his eyes has grown back, but now he has lost almost all the hair on the outside of his back legs.  Currently, we have been advised to continue on the hypoallergenic food,antibiotic and prednisone.  He has responded again to the antibiotic, but this time, he is still severly itchy even on the prednisone.  Our current vet has taken pictures of him and posted his treatments thus far, as well as his picture to an online website where board certified vets give advice.  We have now been advised, that we didnt rule out sarcoptic mange.  We have been told to begin a series of ivermectin shots for 4 weeks to him and all other contact animals, even though our chocolate puppy has NO symptoms at all.  So currently, he is on antibiotics twice a day, the hypoallergenic diet, and we just started the ivermectin shots on Saturday for both dogs.  We have taken off the prednisone since we saw no response to it after a week.  
One more piece of information, my mother-in-law has two puppies from the same litter, and her black lab has the SAME symptoms, but her chocolate has NO symptoms either.  She too has seen four different vets and recieved a wide variety of treatments too, mostly the same treatments our dog has,  except that they did try lime and sulfer dips for two weeks, but she was concerned that her puppy was too young to continue them, so she stopped them, and switched vets.  Our  current vets are "Stumped" and dont really know what is going on with them. I have contacted the breeder and she claims she has had no problems with any of the dogs from her 3 liters.  I have asked her for names and phone numbers of those who have any of her puppies.  Any information you could give us would be great.  Have you ever heard of any situations similar to ours?  Are we on the right path, as far as treatment is concerned?  Please help!

Thanks so much!

Angela Matiyak

Answer
Well it sounds like most of the common diseases have been treated and you should have seen a response.  If the vets suspected demodex, then have the pup dipped in amitraz to see if it will help.  Otherwise, I would recommend having the vet do skin biopsies of active lesions to try and have a veterinary dermatopathologist characterize the type of skin disease present.