Section 287.020 goes on further to state that:
"(3) An injury resulting directly or indirectly from idiopathic causes is not compensable.
(4) A cardiovascular, pulmonary, respiratory, or other disease, or cerebrovascular accident or myocardial infarction suffered by a worker is an injury only if the accident is the prevailing factor in causing the resulting medical condition."
These two sections attempt to limit the compensability of injuries that occur due to something peculiar to an individual. An idiopathic condition is one that is "peculiar to the individual: innate." Alexander v. D.L. Sitton Motor Lines, 851 S.W.2d 525, 527 n.3 (Mo. banc 1993).
Finally, does the employee’s injury come "from a hazard or risk unrelated to the employment to which workers would have been equally exposed outside of and unrelated to the employment in normal nonemployment life." Section 287.020.3(2)(b). There are two steps to this analysis:
The first step is to determine whether the hazard or risk is related or unrelated to the employment. Where the activity giving rise to the accident and injury is integral to the performance of a worker's job, the risk of the activity is related to employment. In such a case, there is a clear nexus between the work and the injury. Where the work nexus is clear, there is no need to consider whether the worker would have been equally exposed to the risk in normal non-employment life. Only if the hazard or risk is unrelated to the employment does the second step of the analysis apply. In that event, it is necessary to determine whether the claimant is equally exposed to this hazard or risk in normal, non-employment life.