An injury, illness, impairment or disease sustained as a consequence of a medical condition covered by the provisions of §30.225(a) must be established with a fully rationalized medical report by a physician that shows the relationship between the injury, illness, impairment or disease and the accepted medical condition. Neither the fact that the injury, illness, impairment or disease manifests itself after a diagnosis of a medical condition covered by the provisions of §30.225(a), nor the belief of the claimant that the injury, illness, impairment or disease was caused by such a condition, is sufficient in itself to prove a causal relationship.