Under the remarks section of each documentation protocol that you follow, you need to provide a medical statement that says which category of illness the condition or symptoms that you have found fall into.

(1) An undiagnosed illness

(2) A diagnosable but medically unexplained chronic multisymptom illness of unknown etiology

(3) A diagnosable chronic multisymptom illness with a partially explained etiology

(4) A disease with a clear and specific etiology and diagnosis

A nexus opinion is not required for categories (1) and (2). However, for any condition that falls into category (3) or (4), a medical nexus opinion with a supporting rationale is generally required to address whether it is "at least as likely as not" that the disability pattern or diagnosed disease is related to a specific exposure event experienced by the Veteran during service in Southwest Asia. However, you are not required to address whether conditions that fall into category (3) or (4) are otherwise related to the Veteran's service (separate and apart from an exposure event) unless VBA specifically requests that you do so.