In order to establish a NEXUS (connection) to your current diagnosis (illness or injury) and your military service, you must have a statement from a competent medical professional.
The degree of certainty of a nexus to service that the medical evidence needs to show is not as difficult to obtain as it might seem. Using the direct service connection method of satisfying the nexus requirement, for example, there need only be medical evidence stating that in the expert’s opinion, it is as likely as not that the current disability resulted from the disease, injury, or precipitating event in service.
Its interesting in my Rating Decision that the VA stated that there is no "diagnosis" of any current illness or injury. The VA decided to combat my claim by taking that route... first. The diagnosis was clear in my Independant Medical Opinion by a private medical expert. The VA did this on 3 of my claims. To date, on these claims, I have not been given a VA C&P examination. The VA took this approach to derail these claims. No, there was no NEXUS for 2 of these 3 claims, but one did have a very strong NEXUS statement by a medical expert in this disability. Still it was shotdown by the VA saying there is no medical diagnosis.... a false statement by the VA.
Obviously I appealed (NOD) all my claims within one month of the Rating Decision. Now, I will work on the other claims that are week on the NEXUS requirement. I still have time in my NOD period.
BEWARE !