A file may contain several possible pathways, but a signed opinion should not treat them as interchangeable. The medical work is different for an event said to cause a disease, a service-connected condition said to cause another disease, and a condition said to worsen another disease. Before ordering an opinion, counsel can test whether each necessary link has evidence behind it.
Write each proposed pathway as a short chain
For direct causation: identify the in-service event or exposure, the current diagnosis, the interval between them, and the mechanism that could connect them. For secondary causation: identify the established condition, its proposed effect, and why another explanation is less persuasive. For aggravation: identify the preexisting or independently caused condition, the claimed additional worsening, its timing, and the basis for distinguishing that worsening from natural progression.
Locate the weak link before commissioning the report
A chain can fail at diagnosis, timing, mechanism, or measurement. A medication may plausibly influence another disease but have started after that disease was already severe. Altered gait may be described in lay history but never observed or measured. A later exposure may be a stronger cause. A useful preliminary screen identifies the weak link and says whether a record, test, or specialty assessment could resolve it.
Ask a narrow question that can be answered
“Address all favorable theories” often produces a sprawling report. A better assignment identifies the most plausible pathway, the key contrary evidence, and any alternate pathway counsel wants considered if the first does not hold. This lets the physician explain why one theory carries the conclusion while another is merely possible or unsupported.
Expect different outcomes across conditions
A multisystem case may support a direct opinion on one diagnosis, a limited aggravation opinion on another, and no conclusion on a third pending testing. That is more useful than a uniform answer. Counsel should know before acceptance when the record makes a signed opinion premature.
Illustrative theory screen
Consider a Veteran with a service-connected knee condition and later lumbar disease. A direct theory might depend on an in-service back injury. A secondary theory might depend on a sustained altered gait preceding lumbar symptoms. An aggravation theory might be relevant if degenerative lumbar disease existed independently but worsened after years of measurable gait impairment. These are different timelines. A clinic note saying “walks normally” during the period of alleged gait change does not necessarily decide the case, but it must be reconciled.
What would change the assignment?
If there is no established lumbar diagnosis, updated imaging or examination may come first. If the gait history exists only as a later recollection, treatment and rehabilitation notes may clarify its duration. If progression matches ordinary degenerative change, the physician must explain why the knee condition caused additional worsening, or say that it cannot be separated. The screen should tell counsel which pathway is ready for an opinion and which is not.
The companion article Direct, Secondary, or Aggravation? explains how to choose the strongest pathway within the finished medical analysis. See also risk factors and causal inference, nexus opinion scope, and when an opinion is worth ordering.