Opinion ID: 1919140
Heading Depth: 1
Heading Rank: 30

Heading: specific causation

Text: [29] As discussed, the district court also determined that Frank's differential etiology proved unreliable. We pause here to note that courts, including this court, have not always been careful to distinguish between differential diagnosis and differential etiology. But differential diagnosis refers to a physician's determination of which one of two or more diseases or conditions a patient is suffering from, by systematically comparing and contrasting their clinical findings. [158] In contrast, etiology refers to determining the causes of a disease or disorder. [159] The court gave three reasons for its conclusion: (1) The record did not show what causes other th[a]n diesel exhaust exposure Frank considered in his differential etiology; (2) Frank `ruled in' diesel exhaust exposure as a possible cause, even though no medical or scientific study concluded that such exposure causes multiple myeloma; and (3) Frank failed to explain why he `ruled out' any other potential causes. [30,31] If an expert's general causation opinion is admissible to show that a suspected agent should be ruled in as a possible cause of the plaintiff's disease, the court must next determine whether the expert performed a reliable differential etiology. [160] To perform a reliable differential etiology, a medical expert must first compile a comprehensive list of hypotheses that might explain the set of salient clinical findings under consideration. [161] At the ruling-in stage of the analysis, an expert's opinion is not reliable if the expert considers a suspected agent that cannot cause the patient's disease. [162] Nor is the opinion reliable if the expert completely fails to consider a cause that could explain the patient's symptoms. [163] [32] Next, the expert engages in a process of elimination, based on the evidence, to reach a conclusion regarding the most likely cause of the disease. [164] At the ruling-out stage of the analysis, the court should focus on whether the expert had a reasonable basis for concluding that one of the plausible causative agents was the most likely culprit for the patient's symptoms. [165] The expert must have good grounds for eliminating potential hypotheses. [166] Unsupported speculation will not suffice. [167] But [w]hat constitutes good grounds for eliminating other potential hypotheses will vary depending upon the circumstances of each case. [168] Under this framework, the district court's first reason was incorrect. Frank's testimony shows that he considered other possible causes of multiple myeloma, including radiation exposure, diabetes, pesticide exposure, and cigarette smoking. The court's second rationale also proves incorrect. Here, the court relied on its finding that Frank improperly ruled in diesel exhaust exposure as the cause of Bradley's cancer even though no medical or scientific study authorizes such a conclusion. We have already determined that the court applied an erroneous standard in ruling that Frank lacked good grounds for believing that Bradley's exposure to diesel exhaust likely caused his multiple myeloma. Finally, the court incorrectly determined that Frank failed to give reasons for ruling out other possible hypotheses. Frank ruled out diabetes and radiation exposure based on Bradley's medical and personal history. In performing a differential etiology, a decision to eliminate an alternative hypothesis based on information gathered by using the traditional tools of clinical medicine will usually have the hallmarks of reliability required under the Daubert/Schafersman framework. These tools include physical examinations, medical and personal histories, and medical testing. [169] Frank explained his reasons for ruling out Bradley's possible pesticide exposure as a teenager and his cigarette smoking. Frank had reviewed epidemiological studies of these agents and believed that they failed to show a causal relationship with multiple myeloma. We emphasized in Carlson v. Okerstrom that the traditional tools for ruling out potential hypotheses in a differential etiology are just guideposts and that often, an expert's decision to rule out an alternative hypothesis will depend on other factors for which clear rules are not available. [170] Here, the evidence does not show that Frank failed to consider other possible hypotheses for Bradley's cancer or to explain why his causation opinion was sound despite BNSF's suggestions of alternative hypotheses. Thus, BNSF's alternative suggestions affect the weight, not the admissibility, of Frank's testimony. [171] Accordingly, on remand, the primary admissibility issue for Frank's opinion on specific causation is whether he had good grounds for ruling in Bradley's diesel exhaust exposure as a plausible cause of his cancer.