My diagnosis for a thin child with this neck would be 'Pellagra' with a Cassal collar well treatable with b-complex factors, if so.
My best wishes.
His regular daily gummy vitamin has vitamin B12 in it. After reading the Wiki article about Pellagra it also says Niacin treats it. The photo on the Wiki article is way more extreme than what my sons skin looks like. There is no itching pain or peeling. Do you think adding Niacin in his diet would somehow help. He gets plenty of Trytophan, turkey sandwiches are usually his after dinner snack. Thanks for the comment ;)
Also Dirty neck of the atopics (family history of allergy) is a look alike. Get the boy's CBC and urine examination also.Addition of B complex factors would help. Do consult your doc. ok?