The courts continue to struggle with the distinction between differential diagnosis and causation assessment. In a recent case Best vs. Lowe’s Home Centers, 563 F.3d 171 (6th Cir. 2009), the Appellate Court overturning the District Court’s exclusion of a plaintiff ENT expert, Dr. Moreno, again found equivalency between the two. Other cases have found them to be separate processes as they, in fact, are.

I have written about this distinction many times, but have never before drawn a picture. Attorneys like words. Scientists like pictures. I cannot imagine describing a biochemical pathway, for example, with words alone. So, I am going to try this the medical way: with a picture. I am hoping that this diagram showing the differential diagnostic pathway, versus the causation methodology pathway clears the matter up. This may be useful to attorneys attempting to exclude medical experts who, in toxic tort matters, are claiming that “differential diagnosis” is their “causation methodology.”


The patient comes to the doctor with symptoms. Symptoms are physical complaints such as: headaches, joint pain, fatigue, insomnia, diarrhea and many, many others. The physician carries out an analytical process comprised of taking a history, performing a physical examination and ordering various tests. This approach constitutes the differential diagnostic process or Clinical Methodology (shown on the diagram) and leads to a diagnosis which is “the actual medical condition.” This is the medical condition which accounts for the symptoms. It is not the cause of that condition. Causation methodology, by contrast, asks:” What caused or contributed to the medical condition elucidated through the clinical process of differential diagnosis?” That requires a separate process (shown on the diagram as “Causation Methodology”) which must consider elements such as: 1. Proof that there is an established, known relationship between the agent at issue and the disease “ General Causation” 2. Proof that the claimant inhaled, ingested or was exposed dermally to an amount of the agent sufficiently high to produce a dose capable of causing the clinical disorder. 3. A finding that the temporal relationship between the exposure and the onset of the disease followed a recognized exposure-disease relationship. and 4. Establishing that other, more or equally-likely causes of the clinical disorder were not present.

In a medical malpractice case, if a patient is harmed, liability may depend upon differential diagnosis alone: e.g. failure to diagnose or reaching the wrong diagnosis (actual medical condition.) By contrast, in a product liability case involving chemicals or pharmaceutical agents, a separate and distinct causation analysis is essential for the determination of what was responsible for the actual medical condition.

In Best v. Lowe’s, the Appellate Court was partially correct and partially incorrect when it overturned the trial court’s exclusion of the ENT expert. It reached a proper conclusion, but its reasoning and its discussion of differential diagnosis were incorrect.

The case involved a claimant who lost his sense of smell allegedly because of exposure to a chemical released in an accident in a Lowe’s store. An ENT physician, Dr. Moreno, worked the patient up (clinical methodology = differential diagnosis) and concluded that the diagnosis was, indeed, anosmia (lost sense of smell). He thereby arrived at the Actual Medical Condition through the differential diagnostic process. He then carried out a causation analysis in which he evaluated alternate causes and discussed them, eliminated them for a variety of reasons, reasoned that the agent was capable of causing the disorder (“general causation”) and concluded that the chemical was the culprit.

The District Court did not argue with the diagnosis or the differential diagnostic process. Rather, it excluded Dr. Moreno’s testimony for lack of proper causation methodology (although, while noting the elements, it did not call it “causation methodology.”) I am not commenting here about the quality of that causation reasoning, having not reviewed all of the underlying facts of the case. From a superficial discussion by the Appellate Court, it would appear that Dr. Moreno may or may not have been wrong in his causal conclusion, but his methodological reasoning seems sound. Thus, this would, I believe, likely go to the quality of the analysis, not to the methodology: a question of fact for the jury. So, it seems that Dr. Moreno actually conducted both a differential diagnosis and a causation analysis. The appellate court, however, did not understand that. They saw his reasoning as a single methodological process which they placed under the rubric of “differential diagnosis.” To that extent they erred. Their conclusion overturning the District Court’s ruling that the testimony was inadmissible was probably correct: their explanation was not.

Another case Lee v. Marlowe, No. 3:08-CV-1739, 2009 WL 2591668, (N.D. Ohio Aug. 20, 2009) illustrates that it is easier for the Court to recognize the nature of differential diagnosis in a more commonly-understood event: an automobile accident as opposed to a chemically-induced injury.

During the evening August 31, 2007, the defendant was traveling westbound on the Ohio Turnpike when his vehicle struck a right-hand guardrail three times, and then swerved across two lanes of traffic, crossing the median separating the eastbound and westbound lanes of traffic, and struck Plaintiff's decedents' vehicle head-on, causing their deaths.

The question was why this happened.

The defendant asserted that the accident was due to a “sudden medical emergency.” Supporting that defense was the unsubstantiated testimony of the defendant’s cardiologist. He opined that the cause was syncope (or fainting). He further sated that he arrived at this conclusion based upon a “differential diagnosis.” The Court did not accept the mere proclamation that he had conducted a proper differential diagnosis. The Court ruled that he had no basis for excluding other causes such as fatigue, impairment or, simply, lack of attention. They, thus, excluded this “differential diagnostic” explanation for the accident and excluded the defense expert’s testimony.

Here the court properly ruled that the supposed “differential diagnosis” was improperly conducted. Thus, determination of the Actual Medical Condition (syncope in this case) was methodologically ill-founded. The physician had no medically reasonable way of ruling out other Conditions besides syncope.

In this case one never got to the cause of the condition, because it was not relevant. The poorly constructed differential diagnosis ended the testimony.
Assume, however, that this was a worker’s compensation case in which a worker fell from a high platform sustaining a serious injury. Assume further that the facts properly supported a diagnosis of “syncope.” Thus, the result of the differential diagnostic process—syncope—was correct. In such a matter the cause of the Condition—the syncope—could be relevant. If it were due to hot working conditions, it would compensable. If it were due to elicit drug use, it might not be (depending upon the State rules.)

To summarize:

Clinical Methodology is the Differential Diagnostic process. This leads to a determination of the Actual Medical Condition which is producing the patient’s physical complaints. Causation Methodology is an entirely separate entity which asks: “What lead to this condition?” Attorneys, defense and plaintiff, and the Courts, need to understand this critical distinction. Defense attorneys particularly need to be aware of the fact that an assertion by a treating physician stating that he/she arrived at a causal conclusion via the standard medical approach of differential diagnosis is incorrect. Differential diagnosis is only the first step in a causation analysis. This must be followed by a separate analytical process as indicated on the accompanying flow diagram.

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Categories: Medical Malpractics

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Chinese Drywall

Posted on March 31, 2009 03:11 by Ronald E. Gots MD PhD

By now many of you have heard of the recent mass tortsinvolving drywall from China. It seems that a very large batch--enough for66,000 homes offgasses a variety of sulfur containing compunds includingcarbonyl sulfide, carbon disulfide and hydrogen sufide to name a few. Thealleged result is corroded copper tubing and, pssibly, wire, and a variety ofhealth complaints (not yet connected scientifically to the drywall.)I justspoke with an old friend who is Florida's state toxicologist. Florida is theepicenter of the issue. These matters are frought with confusion anduncertainty. For one thing, one cannot readily test drywall to identify itspedigree. Bulk testing doesn't do it. Chamber testing for emmissions might, buteven that is uncertain since local drywall kept in proximity to its offgassingcousin appears to adsorb chemicals which can lead to false positive tests.Finally, and quite importantly, levels of any chemicals actually found in homesknown to contain this drywall are quite low making valid health issues quiteunlikely. If anyone would like further information about this, I'd be pleasedto discuss it more fully. 

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Categories: Product Liability | Toxic Tort

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How experts misuse scientific literature:

A critical element of Daubert, specifically stated, is that scientific literature used by experts to support their opinions must be relevant (or, fit) the situation extant in the case. Frequently, experts provide such “support” with long bibliographic lists or stacks of authoritative-seeming articles from scientific journals. This sheer mass of material ostensibly supports your opponent’s opinion. The list may be impressive and daunting. When we do relevance checks, however, we commonly find that many of those citations are irrelevant because they fail to support either general or specific causation in the case at hand. Some of the reasons they fail include:

• Conclusions drawn from animal, not human, studies;
• The quantitative doses or exposure levels in the literature are not comparable to the levels in the case;
• The literature cites the wrong disease;
• The published regulatory data are not applicable to a specific individual;
• The latency period in the literature is inconsistent with the matter;
• The clinical course of treatment in the matter is different; and
• There are many other possibilities as well.

Here’s a simple, non-scientific, example. Assume a man died after being hit by a truck. The operator of the truck was accused of contributing to the death. Plenty of research could be produced to support the proposition that trucks can kill. But wait! This was a child playing with a toy Tonka truck. Clearly, his toy truck could not have been responsible. Thus, all of the vast evidence that trucks can kill is irrelevant in this case. It is often equally irrelevant in cases involving allegations of chemically-induced injuries. However, in these latter cases, the lack of relevance is less apparent to the non-scientist.

Don’t be intimidated by a long reference list or a box of literature.

In a case currently pending before a State Supreme Court, the claimant’s attorney, attempting to salvage her disqualified expert, argued that her expert used a “ weight of evidence approach”. In that matter, she intended “weight” to mean “fully considered” What it actually meant was numbers of pounds. The hundreds of articles weighed a great deal, but they were, in totality or individually, inadequate to support the claim. Most were irrelevant.

On almost any medical or scientific subject, it is possible for an expert to produce dozens, if not hundreds, of articles which are offered to support his/her position. Some may be right on point. Often, many are extraneous or irrelevant, even when they have the name of the chemical, or of the disease, in the title itself. They are simply provided to bolster a poorly-supported position. Attorneys may do the same thing when they compare the facts of their case to a prior precedent, but there are differences. First, the number of legal citations offered is generally less. Second, because they are being used by lawyers to bolster legal arguments against other lawyers’ positions, a critical analysis and response is anticipated. Thus, while the citations may not be directly on point, they either come close, or are readily disputed by opposing counsel. By contrast, attorneys and the Court are in no position, without help, to dissect the hundreds of impressive scientific papers when assessing their relevance. Because of these circumstances, medical and scientific experts are better positioned to mislead.

Case Example

Under Daubert, supporting literature must be “relevant” or “fit” the circumstances at issue, but there are many reasons why imposing stacks of articles may fail the relevancy test. For example:

In certain situations the chemical is known to cause the disease at issue as is the case with Benzene and Leukemia.

Certain relatively high levels of occupational exposures to benzene are clearly connected to a specific form of leukemia: AML (acute myelogenous leukemia). AML is not a terribly rare disease and can arise with no known cause. In fact, most do. It is common for patients who develop leukemia to be asked about “chemical exposures” Some may have worked with or around some chemicals that contain either benzene or other chemicals that contain the name “benzene.” This finding alone may then generate either a workers’ compensation claim, or a liability claim alleging that “benzene” in the workplace caused the leukemia.

A voluminous stack of articles dealing with all aspects of benzene and leukemia accompanied by MSDS’s (the manufacturer’s material safety data sheets--the product information sheets) of chemicals at the workplace containing the word “benzene” will be put forth to support the claim. A closer look at those information sheets, a relevance check, commonly finds them to be irrelevant. Why? Many chemicals which are not benzene contain the name benzene, for example, ethyl benzene, methyl benzene, dichlorobenzene, and many others. These do not cause leukemia. Also, all chemicals derived from petroleum, including paints, paint thinners, and even furniture polish, contain low levels of residual benzene (0.1 % or less). Certain levels, albeit very low, require them to have “benzene” on the label. Exposures to these products containing small amounts of benzene are not connected to leukemias. Again, these MSDS’s may appear persuasive, but they are irrelevant.

Performing a relevancy check

When your experts perform a relevancy check of opposing experts’ literature, they must examine a number of critical questions:

1. Are the studies sufficiently robust and replicated to support a general causation argument?
2. Do the studies establish the potential for the types of clinical effects alleged in the claim? Or, for example, do they investigate subtle biochemical changes which, at present, have no direct clinical applicability?
3. How much effect do the studies show? For example, if a risk is increased by 5%, it is rarely possible to use such studies to allege specific causation in an individual.
4. Were the studies performed in human beings under circumstances similar to those at issue in the case? Agents injected into a mouse’s abdomen are not the same as lower-level materials inhaled by people.
5. What doses were used or observed in those studies? Occupational exposures to a chemical are rarely equivalent or directly applicable to low-level consumer product exposures.

These are just a few of the numerous types of relevancy issues with which we deal daily in our causation analyses. The simple take away message is that daunting lists or piles of scientific and medical articles may be worrisome to attorneys, but they are meaningless to a claim, if they are irrelevant to the specific facts of the case.

Ronald E. Gots, M.D., Ph.D.
International Center for Toxinology and Medicine
Member of the NMAS group
www.ictm.com

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Categories: Daubert | Expert Witnessess

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SCIENTIFIC VERSUS LEGAL CERTAINTY

Posted on February 11, 2009 08:09 by Ronald E. Gots MD PhD

In trial or deposition I have been asked the question: “are you requiring scientific or legal certainty.” This question arises in the context of a causal assessment in, for example, a toxic tort or pharmaceutical liability claim.  The question is designed to be a “gotcha.” Why? Because attorneys believe that scientific certainty is more rigorous (i.e. 95%) than legal certainty (more probable than not or 51%.)  There is truth to that belief, but the question actually compares  apples to oranges.  Scientific certainty is needed for one aspect of an analysis. Legal certainty is required for a different aspect.  Thus, far from a “gotcha,” this question  reflects the attorney’s naivete regarding the application of probabilities to the respective issues–scientific versus legal.

Scientific “certainties” (actually scientists don’t use this legal term of art, but I shall explain it from an attorney’s point of view), is a reflection of the quality of the underlying data.  In other words, are the studies that underlie the claim at issue statistically significant.  Is there a scientifically-accepted likelihood that an observed relationship is not simply due to chance.  That’s where the 95% number comes from.  A p value of 0.05, by convention the cutoff between statistically significant and not, is that 95% likelihood.  But that percentage applies only to the quality of the science used to assess causality in a claim.  If, in fact,  a study showed only a 51% likelihood of reflecting a true, rather than a chance relationship, no scientist, no regulatory body, no one who reviews scientific data would consider that study supportive of a causal relationship.  In the words of legalese: “the relevant scientific community would consider the use of such a study methodologically improper.” 

By contrast, the legal issue of more probable than not or reasonable medical/scientific certainty asks an entirely different question.  First, it assumes that there is recognized and accepted scientific support for a position.  In other words, it first requires that there are studies which meet the generally accepted scientific test of 95%.  Then it asks, is it more probable than not that X caused Y in this case.  It is the answer to that legal question–the more probable than not question–that requires only a 51% assurance.

As an example.  Assume that chemical X has been strongly connected scientifically to disease Y.  Scientific studies have shown (with a p value of 0.05 or  95% confidence) that X is connected to Y.  I have assumed for this argument that there are also sufficient numbers of studies and that they have also shown meaningful attributable risks.  Now assume that we have a claimant who has been exposed to X and has developed disease Y.  In that case general causation–that X can cause Y–is scientifically satisfied.  The next question–did it actually cause this person’s disease requires other elements. Sufficiency of dose, correct timing of exposure and others are among them.  If those, too, are affirmatively satisfied, then an  expert might state that it is more probable than not (greater than 51%) that this claimants disease Y was caused by agent X.  On the other hand, if the studies linking X to Y were not available, or if they were not, by scientific standards (95%), positively connected, then one could not even approach the legal causation question, because there would be no scientific foundation upon which to base it.  Said another way: if X has not been shown scientifically (using scientific measures of statistical significance) to be connected to disease Y then a claim that disease Y came from exposure to agent X, has neither  scientific nor legal merit. 

Therefore, scientific certainty (step 1)  is, indeed, more rigorous than the ultimate test of legal certainty (step2). However one doesn’t get to step 2 without first satisfying step 1.  Thus, both scientific and legal certainty are part of a causal assessment.  And, asking a witness whether his test was one of legal or scientific certainty makes no sense.  The proper answer is “both, each for a different component of the analysis.”

Ronald E. Gots, M.D., Ph.D.
International Center for Toxicology and Medicine
www.ICTM.com

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Categories: Toxic Tort | Scientifc Certainty

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