HS is a heterogeneous group of diseases. Therapy with corticosteroids is used for the
treatment of most and additional therapy is available and dependent upon the type of HS. Newer medicines such as imatinib and mepolizumab are said to be promising. So, should your son have HS, there is reason to be optimistic regarding a positive response to currently available therapy.
You should request, of his doctor, an additional explanation for the tentative diagnosis of pre-hypertension.