Maybe this will help if you can add to your current appeal or need to appeal again.
The following is from a union website in Frequently Asked Questions:
Q: Is a preexisting condition that is aggravated by factors of employment covered under FECA?
A: Disease and illnesses aggravated, accelerated or precipitated by the employment are covered. The employee must submit medical and factual evidence that establishes that the employment aggravated, accelerated or precipitated the condition. OWCP defines the following types of causal relationships:
1. Direct Causation - this type of relationship is shown when the injury or factors of employment through a natural and unbroken sequence, results in the condition claimed (i.e., a fractured arm sustained in a fall would be considered a direct result of the fall).
2. Aggravation - this kind of relationship occurs if a preexisting condition is worsened, either temporarily or permanently by an injury arising in the course of employment (i.e., a back injury may aggravate a claimant's preexisting degenerative disk disease condition, and benefits would be payable for the duration of the aggravation as medically determined).
3. Acceleration - an employment related injury or illness may hasten the development of an underlying condition (i.e., a claimant's diabetes may be accelerated by a work schedule which is so erratic that it prohibits the regular food intake required for this condition).
4. Precipitation - a latent condition which would not have manifested but for the employment (i.e., tuberculosis may be latent for a number of years, then become manifest due to renewed exposure in the work place).