We admit that we never gave much thought to denture adhesive, and until recently our knowledge of denture adhesive products was gained mainly from watching commercials that tend to run during daytime television or reruns of Murder, She Wrote.  But as Bexis says, useful precedent can come from unexpected places, and litigation over the denture adhesive known as Fixodent resulted in a good Daubert ruling in the district court that we reported on here more than three years ago.  The Eleventh Circuit has now affirmed the order in a published decision, so we will again wade into the sticky goo that was the plaintiffs’ experts’ opinions. 

Numerous plaintiffs sued the manufacturer of Fixodent alleging that zinc in the product caused them neurological disorders.  One of the cases was Chapman v. Procter & Gamble Distributing, LLC, 2014 WL4454979 (11th Cir. Sept. 11, 2014), where the plaintiff alleged that she used Fixodent to place her dentures for eight years and experienced a neurological condition known as copper-deficiency myelopathy as a result.  Id. at *1.  The problem for the plaintiffs was that there was no reliable scientific evidence that use of zinc-containing denture adhesive caused the plaintiff’s condition, even assuming that “copper-deficiency myelopathy” even exists.  Sure, the plaintiffs had experts who were willing to offer such opinions as “zinc containing Fixodent denture adhesives are a health hazard and capable of causing severe hematological and neurological injury” and “long-term use of Fixodent (containing 1.69% zinc) will result in . . . neurotoxic, neurologic, and hematologic consequences.”  Id. at *6.  But as we tend to say, just because an expert says something does not make it so.  The plaintiffs’ experts, it turns out, could not connect the dots, resulting in their opinions being excluded and summary judgment being granted for the defendants.  We described it all in some detail in our prior post, and the analysis in the Eleventh Circuit is similar. 

So why then is the Eleventh Circuit’s opinion interesting?  Well, for a number of reasons.

First, the Eleventh Circuit (and the district court before it) applied the “McClain categories.”  Citing McClain v. Metabolife Int’l, Inc., 401 F.3d 1233 (11th Cir. 2005), the Eleventh Circuit stated that in cases where cause and effect has been proved and accepted by the medical community, federal judges “need not undertake an extensive Daubert analysis on the general toxicity question” for the sake of “judicial economy.”  Id. at *3.  In other cases—the “second category”—federal court must undertake a full Daubert analysis before admitting expert opinions into evidence.  Id.  We understand that district judges sometimes express frustration with long and complicated Daubert motions.  We also believe generally that the Eleventh Circuit is about as good a place as any to challenge the admissibility of experts’ opinions, largely because of the McClainopinion.  We are uneasy, however, with dividing cases into categories that offer one side a potential pass when introducing expert opinions on causation. 

Fortunately, the Eleventh Circuit (and the district court before it) placed the expert opinions at issue into “category two” (noting that “[m]illions of consumers have regularly used Fixodent for decades without complaint”) and undertook a full Daubert analysis. 

Which leads us to the second reason why we think this opinion is interesting:  In affirming the exclusion of the plaintiffs’ experts on general causation, i.e., whether the subject denture adhesive could cause copper-deficiency myelopathy, the Eleventh Circuit approved of the district court’s treatment of three concepts that we write on a lot—dose-response relationship, background rate of disease, and epidemiology.  The plaintiff alleged that she swallowed denture adhesive when she used the product to affix her dentures and that it caused an illness-inducing copper deficiency.  That argument begs the question of dose response—i.e., how much adhesive do you have to swallow to get sick?  The Eleventh Circuit put it this way:

Recognizing all substances potentially can be toxic, the judge noted “‘the relationship between the dose and effect (dose-response relationship) is the hallmark of basic toxicology’” and “‘is the single most important factor to consider in evaluating whether an alleged exposure caused a specific adverse effect.’” 

Id. at *6.  The Eleventh Circuit agreed with the district court and its finding that the plaintiffs’ experts could not say (1) how much adhesive must be used for how long to increase the risk of copper deficiency or (2) for how long a person much experience copper deficiency before being at an increased risk of myelopathy.  Id. The lack of evidence on dose-response drove a truck-size hole through the experts’ opinions. 

The Eleventh Circuit similarly approved of the district court’s handling of the background rate of disease and its observation that

[s]ome people use denture cream and some people have a myelopathy; it is possible (and depending on the incidence of myelopathies, likely) that some denture-cream users have an idiopathic myelopathy simply due to the background distribution of that disease.  Without a baseline, any incidence may be coincidence

Id. at *7 (emphasis added).  In other words, just because two events coincide does not mean that one caused the other because the other could have been caused by something else or by nothing at all.  The plaintiffs’ experts did not know the background rate of copper-deficiency myelopathy, which was another “serious methodological deficiency.”  Id. 

So too was the lack of any epidemiological evidence, which is “the best evidence of causation in cases involving toxic substances.”  Id.at *6 (internal quotations omitted).  The plaintiffs’ experts offered lesser forms of evidence—case reports and animal studies—but such information cannot support a causation opinion.  Id.  Case reports are mere anecdotes, which can be useful in generating hypotheses for future study, but cannot prove a cause-and-effect relationship.  Animal studies can similarly provide useful research information, but their results cannot be validly extrapolated to prove causation in humans.  The experts also offered “hypotheses” and “plausible explanations,” which are not scientific data on any level.  Id

Third, we found interesting the Eleventh Circuit’s treatment of specific causation—whether the product “actually caused injury in [the plaintiff’s] particular case.”  Id.  As it turns out, no doctor ever diagnosed the plaintiff with copper-deficiency myelopathy or told her that denture adhesive was at fault, until her retained expert examined her in the course of litigation.  Id. at *8.  Prior to that litigation-driven point, who diagnosed the plaintiff?  Her husband diagnosed her, after conducting research on the Internet.  Id. at *8 n.13.  Hmm.  Do you suppose his Internet search results included attorney advertising?  We don’t know.  Just saying. 

In any event, the plaintiffs’ specific causation expert fell back on what we have called either the “real last refuge of a scoundrel” or “that  most-abused method for determining medical causation,” depending on when you read and who was writing:  the differential diagnosis.  But the differential diagnosis that the plaintiffs’ expert performed was unreliable for the usual reasons—he could not “rule in” the denture cream because it had not been established that the product could cause the plaintiff’s alleged disease and there were numerous potential causes that he did not consider and could not reliably “rule out.”  Id. at **8-9. 

We especially like that the Eleventh Circuit faulted the expert for failing to consider “the possibility of an idiopathic cause.”  Id. at *9.  Many diseases can occur spontaneously without any identifiable cause, and we agree that it is essential to take that into account when determining whether causation can be attributed to any particular factor.  As a practical matter, it is fair to ask whether a plaintiff could ever prove causation through a differential diagnosis when idiopathic disease is on the differential.  After all, how can someone “rule out” a cause that cannot be identified in the first place?  Maybe it’s not possible, but if that reduces the reliance on differential diagnoses in litigation, that would be a change for the better. 

Fourth, we like that the Eleventh Circuit affirmed the exclusion of the Plaintiffs’ final two experts, who intended to opine that the denture cream was toxic.  The Eleventh Circuit cited the following passage with approval:

In short, taking everything together, there is enough data in the scientific literature to hypothesizecausation, but not to infer it.  Hypotheses are verified by testing, not by submitting them to lay juries for a vote.  It may very well be that Fixodent in extremely large doses over many years can cause copper deficiency and neurological problems, but the methodology [the plaintiffs’] experts have used in reaching that conclusion will not reliably produce correct determinations of causation.

Id. at *10 (emphasis added).  The law lags science; it does not lead it, and this is a quote that we can use in urging on district courts in their roles as gatekeepers for scientific opinion.

Without causation experts, summary judgment was a foregone conclusion.  The plaintiffs tried to argue that they could prove causation using their one remaining expert (a biochemist), treating physicians, and the defendants’ experts, but the Eleventh Circuit rejected those arguments, as had the district court, including on the basis that the defendants’ experts held the opinions that the denture adhesive did not cause copper deficiency myelopathy.  Id.at *12. 

We like Chapman because it is a good example of a district court conducting a rigorous Daubert analysis and a Court of Appeals following and affirming that analysis to come to the correct result. The opinion certainly puts a dent in that litigation, and so be it.