Use And Misuse Of Differential Diagnosis

In negligence action, excluding expert differential diagnosis testimony by plaintiff’s treating physician as to the cause of plaintiff’s exercise-induced asthma under Daubert and FRE 702 because a differential diagnosis was inadequate for assessing probable causation where (1) the cause of plaintiff's condition was "largely unknown" in the profession; (2) the expert had no data regarding plaintiff's level of exposure to the claimed cause (freon gas) of the condition, and (3) there was no "temporal proximity" shown between the alleged cause of the condition and the manifestation of the condition, in Bland v. Verizon Wireless L.L.C., 538 F.3d 893 (8th Cir. Aug. 14, 2008) (No. 07-3010)

Differential diagnosis is one approach that may be used in medical expert testimony. As the Eighth Circuit has explained it, a “differential diagnosis [is] a technique that identifies the cause of a medical condition by eliminating the likely causes until the most probable cause is isolated. Turner v. Iowa Fire Equip. Co., 229 F.3d 1202, 1207 (8th Cir. 2000); see Bitler v. A.O. Smith Corp., 391 F.3d 1114, 1123 (10th Cir. 2004) (“‘Differential diagnosis,’ is ‘the determination of which of two or more diseases with similar symptoms is the one from which the patient is suffering, by a systematic comparison and contrasting of the clinical findings.’ In the medical context, differential diagnosis is a common method of analysis, and federal courts have regularly found it reliable under Daubert.”)(quoting Stedman’s Medical Dictionary 492); Clausen v. M/V New Carissa, 339 F.3d 1049, 1058-59 (9th Cir. 2003) (recognizing differential diagnosis as a reliable method; in conducting a differential diagnosis an expert must “rule[] in” all plausible causes for the patient’s condition by compiling “a comprehensive list of hypotheses that might explain the set of salient clinical findings under consideration,” focusing on “which of the competing causes are generally capable of causing the patient’s symptoms or mortality”)). Most often, the Federal Evidence Blog has noted cases in which Circuit's approve the use of a differential diagnosis. Are there any conditions that have compelled a circuit to conclude a differential diagnosis was unreliable and therefore excludable?

The Eighth Circuit considered a negligence action involving the plaintiff's development of exercise-induced asthma, which the plaintiff alleged was caused by actions of the defendant Verizon and its employees. In the case, plaintiff Bland sued Verizon Wireless, L.L.C. and Verizon employee Reid. The plaintiff alleged that she began to suffer from exercise-induced asthma after she ingested Freon, which a Verizon employee had sprayed into her water bottle. The plaintiff was visiting a Verizon store to update her phone, but left her water bottle there when she had finished her business. As a “joke,” Verizon employee Reid sprayed compressed air into the water bottle, which he thought belonged to another employee.


Subscribe Now To The Federal Evidence Review

** Less Than $25 Per Month ** Limited Time Offer **

subscribe today button

The plaintiff returned to retrieve the water bottle and noticed that some employees were laughing. No one told her about the spraying but one person suggested she not drink from the bottle. At home, the plaintiff took a couple of drinks. Her friend took a drink but did not swallow. Both became ill. The police were called and interviewed the Verizon employee who admitted spraying the compressed air. The University of Iowa Hygienic Lab confirmed the bottle had 820 parts per million (ppm) (.08%) of difluoroethane (freon compound). The Iowa Poison Control Center suggested the plaintiff and her friend consult a physician if symptoms of the exposure continued. Five weeks later, the plaintiff was examined by her treating physician who diagnosed “exercise-induced asthma” caused by the inhalation of freon.

After the plaintiff filed her lawsuit in state court, the defendants removed it to federal court. The defendants then moved for summary judgment. The plaintiff relied on the expert testimony of her treating physician as to the causation of the condition. The court excluded the causation testimony as insufficient under the standards of Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579 (1993). In particular, the expert causation testimony was excluded when the trial judge concluded that the treating physician:

“(1) failed scientifically to eliminate other possible causes as part of her differential diagnosis; (2) did not know ‘what amount of exposure to [the] difluroethane-containing Freon causes, or involves an appreciable risk of causing, asthma’; (3) ‘had no good grounds for determining whether Bland was exposed to a sufficient dose of difluoroethane containing Freon to have caused her asthma, because [Dr. Sprince] . . . could not determine or estimate the amount of difluoroethane or Freon . . . Bland was actually or probably exposed [to] when she smelled the water in her water bottle’; (4) could not extrapolate from the existing data because the gap between the data identified and Dr. Sprince’s proferred opinion was ‘“simply too great an analytical gap” . . . to support admissibility (citation omitted); (5) did not offer as evidence any personal experience with ‘treating other patients following a similar exposure to difluoroethane, Freon, or Freon with difluoroethane’; and (6) [the analyst's] reliance on temporal proximity, without more, is insufficient to establish causation.”
Bitler, 391 F.3d at 897. The plaintiff appealed the grant of summary judgment to the defendant and the trial court's exclusion of the expert differential diagnosis testimony.


The circuit affirmed the exclusion of the expert testimony, after explaining the role of the trial court in fulfilling the “gatekeeping” requirements under FRE 702:

“A trial judge must make a preliminary assessment of whether the proffered expert’s methodology is both scientifically valid and applicable to the case. Under Rule 702, as amplified by Daubert, factors bearing upon this determination include whether the expert’s theory or technique (1) can be and has been tested, (2) has been subjected to peer review and publication, (3) has a known or potential rate of error, and (4) has gained general acceptance in the relevant community."
Id. at 593-94. This “gatekeeping requirement” is to ensure that the proffered expert exercises the same “intellectual rigor” in the courtroom as does an expert in the relevant field.” Ahlberg v. Chrysler Corp., 481 F.3d 630, 635 (8th Cir. 2007) (citing Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579, 592-94 (1993)).


In applying this standard, the Eighth Circuit noted briefly three grounds for concluding the proffered differential diagnosis expert testimony was unreliable and excludable. First, a differential diagnosis could not support the causation opinion, noted the circuit. The expert “acknowledged the cause of exercise-induced asthma in the majority of cases is unknown.” Bitler, 391 F.3d at 897. Consequently, the type of comparative assessment required for differential diagnosis could not be performed. The expert also failed to eliminate other possible causes to support a differential diagnosis, and the expert largely relied upon a temporal link for the expert's conclusions about causation.

Second, the expert also lacked knowledge on key areas necessary to determine causation. For example, the treating physician lacked knowledge concerning: “(1) ‘what amount of exposure to [the] difluoroethane-containing Freon causes, or involves an appreciable risk of causing, Asthma’; and (2) what amount of difluoroethane-containing freon ‘Bland was actually or probably exposed [to] when she smelled the water in her water bottle.’” Bitler, 391 F.3d at 898 (citation omitted)). As the circuit explained, “Without knowledge of these data points, [treating physician] Dr. Sprince could not extrapolate from the existing data because, as the district court reasoned, the gap between the data identified and Dr. Sprince’s proferred opinion was “‘simply too great an analytical gap’ . . . to support admissibility.” Bitler, 391 F.3d at 898 (quoting General Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997)).

Finally, the circuit noted that temporal proximity alone was insufficient to show causation. In particular, the circuit was reluctant to rely on temporal proximity where there was a five week delay between exposure and visiting the treating physician. Since the plaintiff could not show causation, summary judgment was warranted.

Subscribe Now To The Federal Evidence Review

** Less Than $25 Per Month ** Limited Time Offer **

subscribe today button

Federal Rules of Evidence
PDF