Circuit Consensus Noted On Use Of Differential Diagnosis Testimony

courtroomExpert’s differential diagnosis of the cause of a medication user’s diabetes (from weight gain allegedly caused by the defendant’s medication) was excluded as unreliable under Daubert because the diagnosis did not consider alternative causes and merely correlated the use of the drug with the plaintiff’s subsequent diabetes, noting other circuits accepting differential diagnosis analysis, in Guinn v. AstraZeneca Pharmaceuticals LP, 602 F.3d 1245 (11th Cir. April 6, 2010) (No. 09-11104)

As noted by the Federal Judicial Center, a “differential diagnosis” is a process where the expert tries to opine on the cause of a person’s condition by isolating the cause of a patient’s symptoms, systematically eliminating all other potential causes. Federal Judicial Center, Reference Manual on Scientific Evidence, 443-44 (2d Ed. 2000) (Reference Guide on Medical Testimony).

In a recent case, the Eleventh Circuit noted a growing consensus among the circuits as to the reliable use of differential diagnosis. The circuit employed a similar definition of “differential diagnosis” – that it “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.” Guinn, 602 F.3d at 1253 (quoting Westberry v. Gislaved Gummi AB, 178 F.3d 257, 262 (4th Cir. 1999) ( Differential diagnosis as “a process of identifying external causes by a process of elimination”).

In the case, plaintiff Guinn filed suit against the defendant (AstraZeneca) for strict product liability, negligence, and fraud in providing her a drug (Seroquel) that she contended caused her to gain weight and from this weight gain, diabetes. The plaintiff claimed that the defendant did not disclose the increased risk of weight gain in users (about one-quarter to one-third of users), marketing the drug without sufficient warnings of this risk or its relationship to the development of diabetes. The plaintiff’s suit was combined with similar suits against the defendant for pre-trial multi-district proceedings. Upon defendant’s motion for summary judgment, the trial court handling the pretrial aspects, held a Daubert hearing involving the plaintiff’s expert witness on causation. This physician opined that the plaintiff’s weight gain of 40 pounds was due to the defendant’s drug, and that this weight gain caused the plaintiff to develop diabetes.

The circuit noted that the plaintiff’s causation expert (Dr. Marks) was problematic. Although she reviewed “Guinn’s weight history, Dr. Marks concluded, ‘based on reasonable medical probability … Seroquel was a cause of [Guinn’s] diabetes.” The plaintiff’s ‘exposure to a medication (Seroquel) … caused weight gain [which] worsened her underlying insulin resistance and likely accelerated the onset‘” of the condition. The expert used “medical literature showing that Seroquel … can cause weight gain.” Because the plaintiff’s diabetes was so “temporal[ly] proxim[ate]” to the plaintiff’s development of diabetes, it must have been the cause of it the expert concluded. The expert “stated she had made no attempt to quantify the amount of weight gain she attributed to Seroquel and had done nothing to rule out other factors as the sole cause of Guinn’s weight gain. Dr. Marks further acknowledged that Seroquel does not cause weight gain in approximately two-thirds of the patients who take the drug.” Guinn, 602 F.3d at 1249.

The expert also admitted that she could not “rule out … other risk factors as the sole cause of Guinn’s diabetes. The expert knew of no methodology for ruling out alternative causes and thus had not attempted to do so. In fact, Dr. Marks agreed Guinn’s other risk factors alone were sufficient to explain the onset of her diabetes. Dr. Marks stated, however, she had “no way of ruling out the Seroquel any more than [she could] rule out any other risk factors.” The defendant’s Daubert challenge to this expert evidence contended that she had “failed to adequately consider and rule out other potential causes of Guinn’s diabetes and that the expert’s “methodology was unreliable because it was based primarily on the temporal proximity of Guinn’s ingestion of Seroquel to her diagnosis of diabetes.”

The circuit noted a general approval of the technique of differential diagnosis. As explained by the circuit:

“Although a reliable differential diagnosis need not rule out all possible alternative causes, it must at least consider other factors that could have been the sole cause of the plaintiff’s injury. As the Fourth Circuit explained in Westberry [v. Gislaved Gummi AB,?? 178 F.3d 257, 265 (4th Cir. 1999)], a “differential diagnosis that fails to take serious account of other potential causes may be so lacking that it cannot provide a reliable basis for an opinion on causation.” See also In re Paoli R.R. Yard PCB Litig., 35 F.3d 711, 759 (3d Cir. 1994) (“[A]t the core of differential diagnosis is a requirement that experts at least consider alternative causes-this almost has to be true of any technique that tries to find a cause of something.”). As other circuits have recognized, an expert ‘must provide a reasonable explanation as to why “he or she has concluded that [any alternative cause suggested by the defense] was not the sole cause’ ” of the plaintiff’s injury. Best v. Lowe’s Home Ctrs., Inc., 563 F.3d 171, 179 (6th Cir. 2009) (quoting Paoli, 35 F.3d at 758 n.27); see also Lauzon v. Senco Prods., Inc., 270 F.3d 681, 694 (8th Cir. 1994) (stating an expert must “be able to explain why other conceivable causes are excludable”); Westberry, 178 F.3d at 265 (holding an expert must provide some explanation of why other potential causes were not the sole cause); Kannankeril v. Terminix Int’l, Inc., 128 F.3d 802, 808 (3d Cir. 1997) (holding that after a defendant identifies a plausible alternative cause, it is “necessary for the plaintiff’s expert to offer a good explanation as to why his or her conclusion remains reliable”).”

Guinn, 602 F.3d at 1253.

In a careful analysis, the circuit went on to extensively consider the trial court’s assessment of the differential diagnosis proffered by the plaintiff’s expert. Ultimately, the circuit concluded that the trial judge did not abuse his discretion in excluding the plaintiff’s differential diagnosis evidence. The expert offered merely the ipse dixit of the expert as the basis for concluding that only the defendant’s drug was the cause of the plaintiff’s condition. But the expert herself admitted that there was no method for assessing whether one’s weight gain was due to the defendant’s drug or was simply the effect of the normal fluctuations that occurred in the plaintiff’s weight throughout life. In light of the fact that the plaintiff also had numerous other risk factors for diabetes (each of which could be sufficient in themselves to cause plaintiff’s diabetes), the failure of the expert to assess the relative contribution of each factor undermined the reliability of her analysis. Guinn, 602 F.3d at 1257.

While the Guinn case provides a careful example of how to assess a differential diagnosis, it also serves as a source on the growing acceptance of the technique. A solidly executed differential diagnosis is likely to find ready support in the Third, Fourth, Sixth and Eighth Circuits – and as Guinn demonstrates, the Eleventh Circuit.


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