Toxic Tort Cause & Effect & Differential Diagnosis

In worker's suit after exposure to certain harmful chemicals in the workplace as a result of the lack of functioning of hood made by defendant, excluding under FRE 702 an opinion by the plaintiff's toxicology expert regarding the specific cause of the plaintiff's lung disease; while the witness was qualified to testify as to the plaintiff's general medical condition, his differential diagnosis fatally failed to deploy the requisite "two-step process in examining the admissibility of causation evidence in toxic tort cases" since neither he nor any other expert witness presented reliable epidemiological or controlled studies of the charged chemical residues in causing conditions such as that of the plaintiff, in Johnson v. Arkema, Inc., 685 F.3d 452 (5th Cir. June 20, 2012) (No. 11-50139)

A typical toxic substance exposure case often requires expert opinion evidence. One approach commonly used to explain the cause of a plaintiff's injury involves the use of “differential diagnosis.” This technique, as the Fifth Circuit recently noted, involves the court in determining the disease process that caused a plaintiff’s symptoms by employing a "a two-step process.... First, the district court must determine whether there is general causation. Second, if it concludes that there is admissible general-causation evidence, the district court must determine whether there is admissible specific-causation evidence." Johnson, 685 F.3d at 468 (quoting Knight, 482 F.3d at 351 (internal quotation marks and citations omitted)). This is essentially a type of data sorting process.

In the Fifth Circuit case, plaintiff Johnson sought payment of injuries he suffered from exposure to toxic chemicals when a device made by the defendant for application of the chemicals failed to perform properly, allegedly exposing him to toxic chemicals. The plaintiff alleged the he felt this exposure immediately upon using the device and that over time it resulted in a "lung condition [that] progressively worsened over the course of the years following the exposure incidents, culminating in a diagnosis of severe restrictive lung disease and pulmonary fibrosis." Johnson, 685 F.3d at 457. In filing a toxic tort action against the defendant maker of the device, the plaintiff presented expert medical testimony that the exposure to the escaping chemicals had caused his breathing difficulties. The trial court excluded the plaintiff's experts on the causation issue, finding that while the plaintiff presented reliable expert evidence on whether the plaintiff's condition had some specific relationship to his exposure to the escaping chemicals, his experts failed to establish that generally the chemical resulted in his development of the condition which was the basis of the suit.

The plaintiff appealed the result of the case by challenging the trial judge's exclusion of his expert testimony. The judge ruled that while the plaintiff's expert [Grodzin] could offer his medical diagnosis that Johnson suffers from 'interstitial lung disease resulting in a severe restrictive condition, and pulmonary fibrosis,' it erred in excluding the expert's "opinion regarding the cause of Johnson's lung disease." The plaintiff argued that because the expert had performed a "differential diagnosis" of the cause of the plaintiff's condition, it was far from reliable per se scientific evidence.

The Circuit differed, citing an analysis by the Fourth Circuit which observed that the "'...reliable differential diagnosis typically, though not invariably, is performed after “physical examinations, the taking of medical histories, and the review of clinical tests, including laboratory tests,” and generally is accomplished by determining the possible causes for the patient's symptoms and then eliminating each of these potential causes until reaching one that cannot be ruled out or determining which of those that cannot be excluded is the most likely." Johnson, 685 F.3d at 468 (emphasis added) (citing Westberry v. Gislaved Gummi AB, 178 F.3d 257, 262 (4th Cir. 1999) (quoting Kannankeril v. Terminix Int'l, Inc., 128 F.3d 802, 807 (3d Cir. 1997)).

While a differential diagnosis often results in reliable expert opinion, this is not a foregone conclusion. In this the circuit found the plaintiff's differential diagnosis evidence lacking:
[B]efore courts can admit an expert's differential diagnosis, which, by its nature, only addresses the issue of specific causation, the expert must first demonstrate that the chemical at issue is actually capable of harming individuals in the general population, thereby satisfying the general causation standard.
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Here ... Dr. Grodzin's differential diagnosis is based on the presumption that [chemicals plaintiff was exposed to]MBTC and HCl are actually capable of causing restrictive lung disease and pulmonary fibrosis in the general population. Dr. Grodzin has not presented any reliable or relevant scientific evidence to bolster this presumption. Instead, Dr. Grodzin essentially relied on the same scientific evidence and reached the same conclusions as [plaintiff's expert witness] Dr. Schlesinger. As we have explained, the district court did not abuse its discretion in excluding Dr. Schlesinger's opinion, thus negating Dr. Schlesinger's ability to satisfy the general causation requirement. Consequently, the fact that Dr. Grodzin conducted a differential diagnosis does not save his opinion from the same fate as Dr. Schlesinger's opinion.
* * *
The district court did not abuse its discretion in excluding Dr. Grodzin's causation opinion because, irrespective of the differential diagnosis, Dr. Grodzin is unable to
Johnson, 685 F.3d at 469 (citations omitted).

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