Causal Relationship

4. Causal Relationship

Medical causation must be proved to a reasonable degree of medical certainty and cannot be based on mere speculation.

An identifiable factor (accident) that results in a medically identifiable condition ( injury or illness).

American Medical Association: Guides to the Evaluation of Permanent Impairment, fifth edition. Chicago, American Medical Association 2001

Causal opinions in reports and testimony must be given in terms of reasonable medical probability or certainty. (more probably than not).

American Medical Association: Disability Evaluation, second edition. Chicago, AMA 2003.

Probability, simply means that something is more likely than not (51% or greater). If the confidence is equal to or less than 50% it is merely a possibility.

American Medical Association: Guides to the Evaluation of Permanent Impairment, sixth edition. Chicago, American Medical Association, 2008

Criteria for Asserting the Existence of a Causal Relationship

Temporal Relationship       Cause should come before effect.  The interval between the two should be consistent with what is found in reports or studies of similar injuries.

Mechanism                           Must be anatomically and physiologically plausible.

Contiguity                              Should be a clear relationship between cause and effect, with an increase in exposure (dose or duration) leading to an increase in effect

Consistency                          Exposure should consistently cause the disease or injury under investigation.

Specificity                              Should be a relative absence of other factors or conditions which “explain” the disease.

Coherence                            Presumption of work-relatedness in an individual case or documented injury should be consistent with the medical literature.

American Medical Association: Disability Evaluation, second edition. Chicago, AMA 2003.

A causal relationship is biologically plausible when:

•         The relationship between the medical condition and the injury can be explained anatomically or physiologically.

•         The duration, intensity, or mechanism of exposure or injury was sufficient to cause the illness or injury in questions.

•         There is evidence suggesting that the exposure is consistently or reliably associated with the process under investigation in the population under investigation or in peer-reviewed literature.

•         Cause and effect are contiguous.

•         There is literature providing biologic or statistical evidence indicating that the symptoms or disorder could develop as a result of the exposure (coherence).

•         There is specificity of the association for the injury (i.e., the absence of other factors)

Combinations, of direct trauma and a preexisting disease process are more difficult to assess for causality and apportionment. One must determine, if the requirements of temporal relationship, biologic plausibility, literature support, and sufficient injury have been met. This includes and assessment of whether the trauma would have caused the disease in the absence of the preexisting process.  American Medical Association: Disability Evaluation, second edition. Chicago, AMA 2003, page 99 -100.