The Federal Judicial Center’s Reference Manual on Scientific Evidence has avoided any clear, consistent guidance on the issue of case reports. The Second Edition waffled:

“Case reports lack controls and thus do not provide as much information as controlled epidemiological studies do. However, case reports are often all that is available on a particular subject because they usually do not require substantial, if any, funding to accomplish, and human exposure may be rare and difficult to study. Causal attribution based on case studies must be regarded with caution. However, such studies may be carefully considered in light of other information available, including toxicological data.”

F.J.C. Reference Manual on Scientific Evidence at 474-75 (2d ed. 2000). Note the complete lack of discussion of base-line risk, prevalence of exposure, and external validity of the “toxicological data.”

The second edition’s more analytically acute and rigorous chapter on statistics generally acknowledged the unreliability of anecdotal evidence of causation. See David Kaye & David Freedman, “Reference Guide on Statistics,” in F.J.C. Reference Manual on Scientific Evidence 91 – 92 (2d ed. 2000).

The Third Edition of the Reference Manual is even less coherent. Professor Berger’s introductory chapter[1] begrudgingly acknowledges, without approval, that:

“[s]ome courts have explicitly stated that certain types of evidence proffered to prove causation have no probative value and therefore cannot be reliable.⁵⁹”

The chapter on statistical evidence, which had been relatively clear in the second edition, now states that controlled studies may be better but case reports can be helpful:

“When causation is the issue, anecdotal evidence can be brought to bear. So can observational studies or controlled experiments. Anecdotal reports may be of value, but they are ordinarily more helpful in generating lines of inquiry than in proving causation.¹⁴”

Reference Manual at 217 (3d ed. 2011). The “generally” is given no context or contour for readers. These authors fail to provide any guidance on what will come from anecdotal evidence, or when and why anecdotal reports may do more than merely generating “lines of inquiry.”

In Matrixx Initiatives Inc. v. Siracusano, 131 S. Ct. 1309 (2011), the Supreme Court went out of its way, way out of its way, to suggest that statistical significance was not always necessary to support conclusions of causation in medicine. Id. at 1319. The Court cited three Circuit court decisions to support its suggestion, but two of three involved specific causation inferences from so-called differential etiologies. General causation was assumed in those two cases, and not at issue[2]. The third case, the notorious Wells v. Ortho Pharmaceutical Corp., 788 F. 2d 741, 744–745 (11^th Cir. 1986), was also cited in support of the suggestion that statistical significance was not necessary, but in Wells, the plaintiffs’ expert witnesses actually relied upon studies that claimed at least nominal statistical significance. Wells was and remains representative of what is possible and results when trial judges ignore the constraints of study validity. The Supreme Court, in any event, abjured any intent to specify “whether the expert testimony was properly admitted in those cases [Wells and others],” and the Court made no “attempt to define here what constitutes reliable evidence of causation.” 131 S. Ct. at 1319.

The causal claim in Siracusano involved anosmia, loss of the sense of smell, from the use of Zicam, zinc gluconate. The case arose from a motion to dismiss the complaint; no evidence was ever presented or admitted. No baseline risk of anosmia was pleaded; nor did plaintiffs allege that any controlled study demonstrated an increased risk of anosmia from nasal instillation of zinc gluconate. There were, however, clinical trials conducted in the 1930s, with zinc sulfate for poliomyelitis prophylaxis, which showed a substantial incidence of anosmia in the treated children[3]. Matrixx tried to argue that this evidence was unreliable, in part because it involved a different compound, but this argument (1) in turn demonstrated a factual issue that required discovery and perhaps a trial, and (2) traded on a clear error in asserting that the zinc in zinc sulfate and zinc gluconate were different, when in fact they are both ionic compounds that result in zinc ion exposure, as the active constituent.

The position stridently staked out in Matrixx Initiatives is not uncommon among defense counsel in tort cases. Certainly, similar, unqualified statements, rejecting the use of case reports for supporting causal conclusions, can be found in the medical literature[4].

When the disease outcome has an expected value, a baseline rate, in the exposed population, then case reports simply confirm what we already know: cases of the disease happen in people regardless of their exposure status. For this reason, medical societies, such as the Teratology Society, have issued guidances that generally downplay or dismiss the role that case reports may have in the assessment and determination of causality for birth defects:

“5. A single case report by itself is not evidence of a causal relationship between an exposure and an outcome.  Combinations of both exposures and adverse developmental outcomes frequently occur by chance. Common exposures and developmental abnormalities often occur together when there is no causal link at all. Multiple case reports may be appropriate as evidence of causation if the exposures and outcomes are both well-defined and low in incidence in the general population. The use of multiple case reports as evidence of causation is analogous to the use of historical population controls: the co-occurrence of thalidomide ingestion in pregnancy and phocomelia in the offspring was evidence of causation because both thalidomide use and phocomelia were highly unusual in the population prior to the period of interest. Given how common exposures may be, and how common adverse pregnancy outcome is, reliance on multiple case reports as the sole evidence for causation is unsatisfactory.”

The Public Affairs Committee of the Teratology Society, “Teratology Society Public Affairs Committee Position Paper Causation in Teratology-Related Litigation,” 73 Birth Defects Research (Part A) 421, 423 (2005).

When the base rate for the outcome is near zero, and other circumstantial evidence is present, some commentators insist that causality may be inferred from well-documented case reports:

“However, we propose that some adverse drug reactions are so convincing, even without traditional chronological causal criteria such as challenge tests, that a well documented anecdotal report can provide convincing evidence of a causal association and further verification is not needed.”

Jeffrey K. Aronson & Manfred Hauben, “Drug safety: Anecdotes that provide definitive evidence,” 333 Brit. Med. J. 1267, 1267 (2006) (Dr. Hauben was medical director of risk management strategy for Pfizer, in New York, at the time of publication). But which ones are convincing, and why?

        *        *        *        *        *        *        *        *        *

Dr. David Schwartz, in a recent blog post, picked up on some of my discussion of the gadolinium case reports (see here and there), and posited the ultimate question: when are case reports sufficient to show causation? David Schwartz, “8 Examples of Causal Inference Without Data from Controlled Studies” (Dec. 14, 2014).

Dr. Schwartz discusses several causal claims, all of which gave rise to litigation at some point, in which case reports or case series played an important, if not dispositive, role:

1.      Gadolinium-based contrast agents and NSF
2.      Amphibole asbestos and malignant mesothelioma
3.      Ionizing radiation and multiple cancers
4.      Thalidomide and teratogenicity
5.      Rezulin and acute liver failure
6.      DES and clear cell vaginal adenocarcinoma
7.      Vinyl chloride and angiosarcoma
8.      Manganese exposure and manganism

Dr. Schwartz’s discussion is well worth reading in its entirety, but I wanted to emphasize some of Dr. Schwartz’s caveats. Most of the exposures are rare, as are the outcomes. In some cases, the outcomes occur almost exclusively with the identified exposures. All eight examples pose some danger of misinterpretation. Gadolinium-based contrast agents appear to create a risk of NSF only in the presence of chronic renal failure. Amphibole asbestos, and most importantly, crocidolite causes malignant mesothelioma after a very lengthy latency period. Ionizing radiation causes some cancers that are all-too common, but the presence of multiple cancers in the same person, after a suitable latency period, is distinctly uncommon, as is the level of radiation needed to overwhelm bodily defenses and induce cancers. Thalidomide was associated by case reports fairly quickly with phocomelia, which has an extremely low baseline risk. Other birth defects were not convincingly demonstrated by the case series. Rezulin, an oral antidiabetic medication, was undoubtedly causally responsible for rare cases of acute liver failure. Chronic liver disease, however, which is common among type 2 diabetic patients, required epidemiologic evidence, which never materialized[5].

Manganism, by definition, is the cause of manganism, but extremely high levels of manganese exposure, and specific speciation of the manganese, are essential to the causal connection. Manganism raises another issue often seen in so-called signature diseases: diagnostic accuracy. Unless the diagnostic criteria have perfect (100%) specificity, with no false-positive diagnoses, then once again, we expect false-positive cases to appear when the criteria are applied to large numbers of people. In the welding fume litigation, where plaintiffs’ counsel and physicians engaged in widespread, if not wanton, medico-legal screenings, it was not surprising that they might find occasional cases that appeared to satisfy their criteria. Of course, the more the criteria are diluted to accommodate litigation goals, the more likely there will be false positive cases.[6]

Dr. Schwartz identifies some common themes and important factors in identifying the bases for inferring causality from uncontrolled evidence:

“(a) low or no background rate of the disease condition;

(b) low background rate of the exposure;

(c) a clear understanding of the mechanism of action.”

These factors and perhaps others should not be confused with strict criteria here. The exemplar cases suggest a family resemblance of overlapping factors that help support the inference, even against the most robust skepticism.

In litigation, defense counsel typically argue that analytical epidemiology is always necessary, and plaintiffs’ counsel claim epidemiology is never needed. The truth is more nuanced and conditional, but the great majority of litigated cases do require epidemiology for health effects because the claimed harms are outcomes that have an expected incidence or prevalence in the exposed population irrespective of exposure.

[1] Reference Manual on Scientific Evidence at 23 (3d ed. 2011) (citing “Cloud v. Pfizer Inc., 198 F. Supp. 2d 1118, 1133 (D. Ariz. 2001) (stating that case reports were merely compilations of occurrences and have been rejected as reliable scientific evidence supporting an expert opinion that Daubert requires); Haggerty v. Upjohn Co., 950 F. Supp. 1160, 1164 (S.D. Fla. 1996), aff’d, 158 F.3d 588 (11th Cir. 1998) (“scientifically valid cause and effect determinations depend on controlled clinical trials and epidemiological studies”); Wade-Greaux v. Whitehall Labs., Inc., 874 F. Supp. 1441, 1454 (D.V.I. 1994), aff’d, 46 F.3d 1120 (3d Cir. 1994) (stating there is a need for consistent epidemiological studies showing statistically significant increased risks).”)

[2] Best v. Lowe’s Home Centers, Inc., 563 F. 3d 171, 178 (6^th Cir 2009); Westberry v. Gislaved Gummi AB, 178 F. 3d 257, 263–264 (4^th Cir. 1999).

[3] There may have been a better argument for Matrixx in distinguishing the method and place of delivery of the zinc sulfate in the polio trials of the 1930s, but when Matrixx’s counsel was challenged at oral argument, he asserted simply, and wrongly, that the two compounds were different.

[4] Johnston & Hauser, “The value of a case report,” 62 Ann. Neurology A11 (2007) (“No matter how compelling a vignette may seem, one must always be concerned about the reliability of inference from an “n of one.” No statistics are possible in case reports. Inference is entirely dependent, then, on subjective judgment. For a case meant to suggest that agent A leads to event B, the association of these two occurrences in the case must be compared to the likelihood that the two conditions could co-occur by chance alone …. Such a subjective judgment is further complicated by the fact that case reports are selected from a vast universe of cases.”); David A. Grimes & Kenneth F. Schulz, “Descriptive studies: what they can and cannot do,” 359 Lancet 145, 145, 148 (2002) (“A frequent error in reports of descriptive studies is overstepping the data: studies without a comparison group allow no inferences to be drawn about associations, causal or otherwise.”) (“Common pitfalls of descriptive reports include an absence of a clear, specific, and reproducible case definition, and interpretations that overstep the data. Studies without a comparison group do not allow conclusions about cause and disease.”); Troyen A. Brennan, “Untangling Causation Issues in Law and Medicine: Hazardous Substance Litigation,” 107 Ann. Intern. Med. 741, 746 (1987) (recommending that testifying physicans “[a]void anecdotal evidence; clearly state the opposing side is relying on anecdotal evidence and why that is not good science.”).

[5] See In re Rezulin, 2004 WL 2884327, at *3 (S.D.N.Y. 2004).

[6] This gaming of diagnostic criteria has been a major invitation to diagnostic invalidity in litigation over asbestosis and silicosis in the United States.

Gadolinium (Gd) is a rare earth element. In its ionic form (+3), gadolinium is known to be highly toxic to humans. Gadolinium is strongly paramagnetic, which makes it a valuable contrast agent in for magnetic resonance imaging (MRI). The gadolinium is administered intravenously in a chelated form before MRI. In its chelated form, the ion is escorted out of the body through the kidneys before exposure to free Gd ion occurs. Or that was the theory.

Nephrogenic systemic fibrosis (NSF) is a rare, painful, incurable progressive connective tissue disease. NSF manifests with skin thickening and fibrosis, tethering, which means it cannot be pulled away from body. Some patients may develop extracutaneous fibrosis of muscle, lymph nodes, pleura, and other internal organs. Elana J. Bernstein, Christian Schmidt-Lauber, and Jonathan Kay, “Nephrogenic systemic fibrosis: A systemic fibrosing disease resulting from gadolinium exposure,” 26 Best Practice & Research Clin. Rheum. 489, 489 (2012).

As a diagnostic entity, NSF is a relatively recent discovery. The first case was noted in 1997, in California. Within a few years, the differential diagnostic criteria to distinguish NSF from other fibrotic diseases were developed. Centers for Disease Control, “Fibrosing skin condition among patients with renal disease–United States and Europe, 1997–2002,” 51 MMWR Morbidity and Mortality Weekly Report 25 (2002). Physicians identified the condition among patients with renal insufficiency who had received MRI with a gadolinium-based contrast agent (GBCA). Given the rarity of both the exposure (GBCA and renal insufficiency) and the outcome (NSF), the relationship between NSF and the use of gadolinium-containing contrast agents for magnetic resonance imaging (MRI) was discovered largely from case reports. A case registry is maintained at Yale University, and has identified 380 cases to date. Shawn E. Cowper, “Nephrogenic Systemic Fibrosis” at the website for The International Center for Nephrogenic Systemic Fibrosis Research (ICNSFR) [last updated June 15, 2013).

The little epidemiology that exists on the subject generally has found that all “cases” had exposure to Gd[1]. Or almost all. There have been occasional cases found without reported exposure to GBCA. Indeed, one case of NSF without prior GBCA was reported last month in the dermatological literature. C. Ross, N. De Rosa, G. Marshman, D. Astill, “Nephrogenic systemic fibrosis in a gadolinium-naïve patient: Successful treatment with oral sirolimus,” Australas. J. Dermatol. (2014); doi: 10.1111/ajd.12176. [Epub ahead of print].

In litigation, the usual scenario is that plaintiffs and their counsel and expert witnesses want to offer case reports or case series as probative of a causal association between an exposure and a particular disease outcome. In the silicone gel breast implant litigation, women, who self-characterized themselves “victims,” shouted outside courtrooms, “We are the evidence.”

When the outcome in question has a baseline rate, and the exposure is widespread, this strategy is usually illegitimate and most courts have limited or prohibited the obvious attempt to prejudice the jury by the use of evidence that has little or no probative value.

The causal connection between NSF and GBCA, described above, was postulated on the basis of case reports, but this is not really a rejection of the general rule about case reports. NSF is an extremely rare outcome, and GBCA administered to patients with serious kidney insufficiency is a fairly rare exposure. In addition, gadolinium ion has a known human toxicity, and the connection between renal insufficiency and Gd toxicity is rather straightforward. The insufficiency of the kidney function results in longer “in residence” times for the GBCA, with the consequence that the gadolinium disassociates from its chelating agent, and the free Gd ion does its damage. Furthermore, biopsies of affected tissues show an uptake of gadolinium in NSF patients.

   *   *   *   *   *   *   *   *

GE Healthcare manufactures Omniscan, a GBCA, for use as an MRI-contrast medium. Given the recently discovered dangers of GBCAs in vulnerable patients, Omniscan has been a magnet for lawsuits, with the peak intensity of the litigation field in the MDL courtroom of federal district courtroom of Judge Dan Polster. Judge Polster tried the first Omniscan case, which resulted in a verdict for the plaintiff. GE appealed, complaining about several of Judge Polster’s rulings, including the uneven handling of case reports. Last month, the Sixth Circuit affirmed. Decker v. GE Healthcare Inc., ___ F.3d ___, 2014 FED App. 0258P, 2014 U.S. App. LEXIS 20049 (6th Cir. Oct. 20, 2014).

General causation between GBCAs and NSF was apparently not disputed in Decker. Although plaintiffs in the GBCA litigation established the causality of GABC in producing NSF, by case reports, Judge Polster refused to permit GEHC’s expert witnesses to testify about their reliance upon case reports of gadolinium-naïve cases of NSF; that is, the court disallowed testimony about reported cases that occurred in the absence of GBCA exposure[2]. Id. at *9. Judge Polster found that the reported gadolinium-naïve case reports were “methodologically flawed” because they did not adequately show that the NSF patients in question lacked Gd exposure, with tissue biopsy or other means. Id. at * 10. The district court speculated that there may have Gd exposure from a non-MRI procedure, but never explained what non-MRI procedure would involve internal administration of GBCA. Nor did the district court address the temporal relationship between this undocumented, conjectured non-MRI gadolinium-based imaging procedure and the onset of the reported patient’s NSF.

Before trial defendant GEHC moved for reconsideration of the district court’s previous decision on defensive use of gadolinium-naïve case reports, based upon on a then recent publication of a “purported” case of gadolinium-naïve NSF. Id. at *8. A quick read of the late-breaking case study shows that it was more than a “purported” case. A.A. Lemy, et al., “Revisiting nephrogenic systemic fibrosis in 6 kidney transplant recipients: a single-center experience,” 63 J. Am. Acad. Dermatol. 389 (2010). The cited paper by Lemy had diagnosed NSF in a patient without GBCA exposure, and mass spectrometry testing of affected tissue revealed no Gd. The district court, however, dismissed the Lemy case as irrelevant unless GEHC’s expert witnesses could demonstrate that Lemy’s patient number 5 and the plaintiff were so clinical similar that “it was probable that Mr. Decker’s NSF was not caused by his 2005 Omniscan [exposure].”

The Sixth Circuit affirmed this “tails they win; heads you lose” approach to gatekeeping as all within the scope of the district court’s exercise of discretion. Lemy’s case number 5 and Mr. Decker both had NSF, and yet the courts do not describe clinical varieties among NSF, which vary based upon their relatedness to gadolinium exposure. It would seem that the courts were imposing an extremely heavy burden on the defense to show that the gadolinium-naïve cases were absolutely free of Gd exposure, and that they resembled the particular plaintiff’s NSF diagnosis in every respect. Without any evidence of diagnostic disease criteria sensitivity and specificity, and positive predictive value for the criteria, the district and the appellate courts seem to have accepted glib demands for absolute identity between the plaintiff’s NSF manifestation and any candidate Gd-free NSF case. Given that there is clinical heterogeneity among Gd-NSF cases, and that causality was basically inferred from cases and case series, the courts’ reasoning seems strained.

The appellate court also seemed blithely unaware of the fallacious circularity of permitting a diagnostic entity to be defined based upon exposure, thereby preventing any fair test of the hypothesis that all NSF cases are caused by gadolinium. This fallacy was advanced in the silicone gel breast implant litigation, where the litigation industry shrank from claims that silicone caused classic connective tissue diseases, in the face of exculpatory epidemiologic studies. The claimants retreated to a claim that silicone caused a “new” disease that was defined by mostly vague, self-reported symptoms [so very different from NSF in this respect], in conjunction with silicone exposure. The court-appointed expert witnesses, however, would have none of these shenanigans:

“The National Science Panel concluded that they do not yet support the inclusion of SSRD [systemic silicone-related disease] in the list of accepted diseases, for 4 reasons. First, the requirement of the inclusion of the putative cause (silicone exposure) as one of the criteria does not allow the criteria set to be tested objectively without knowledge of the presence of implants, thus incurring incorporation bias (27).”

Peter Tugwell, George Wells, Joan Peterson, Vivian Welch, Jacqueline Page, Carolyn Davison, Jessie McGowan, David Ramroth, and Beverley Shea, “Do Silicone Breast Implants Cause Rheumatologic Disorders? A Systematic Review for a Court-Appointed National Science Panel,” 44 Arthritis & Rheumatism 2477, 2479 (2001) (citing David Sackett, “Bias in analytic research,” 32 J. Chronic Dis. 51 (1979)).

Of course, NSF does not share the dubious provenance of SSRD, or SAD [silicone-associated disorder] as it was sometimes known. Still, the analytic studies that have shown that NSF cases all, or mostly, had GBCA exposure, explicitly refrained from defining the NSF case as including gadolinium exposure.

Decker is thus a curious case. The trial and appellate court talked about preventing the defense expert witnesses from relying upon case reports that were “methodologically flawed,” but the courts never mentioned Federal Rule of Evidence 703, which should have been the basis for such selective pruning of the expert witnesses’ reliance materials. And then there is the matter that even if GEHC were correct about Gd-free NSF cases, the attributable risk for NSF to prior Gd exposure is almost certainly very high, and the debate over whether NSF is a “signature” disease was not likely going to affect the case outcome.

Decker can perhaps best be understood as a dispute about specific causation, with established general causation, in which the relative risk of NSF from GBCA exposure is extraordinarily high among patients with renal insufficiency. If there are other causes of NSF, they are considerably more rare than GBCA/renal insufficiency exposed cases. In the face of this very high attributable risk, GE’s expert witnesses’ discussions of an idiopathic or other cause was too speculative to pass muster under Rule 702.

[1] Elana J. Bernstein, Tamara Isakova, Mary E. Sullivan, Lori B. Chibnik, Myles Wolf & Jonathan Kay, “Nephrogenic systemic fibrosis is associated with hypophosphataemia: a case–control study,” 53 Rheumatology 1613 (2014); T.R. Elmholdt, M. Pedersen, B. Jørgensen, K. Søndergaard, J.D. Jensen, M. Ramsing, and A.B. Olesen, “Nephrogenic systemic fibrosis is found only among gadolinium-exposed patients with renal insufficiency: a case-control study from Denmark,” 165 Br. J. Dermatol. 828 (2011); P. Marckmann, “An epidemic outbreak of nephrogenic systemic fibrosis in a Danish hospital,” 66 Eur. J. Radiol. 187 (2008) (reporting all patients had gadodiamide-enhanced magnetic resonance imaging and severe renal insufficiency before onset of NSF); P. Marckmann, L. Skov, K. Rossen, J.G. Heaf, and H.S. Thomsen, “Case-control study of gadodiamide-related nephrogenic systemic fibrosis,” 22 Nephrol. Dialysis &Transplant. 3174 (2007) (all 19 cases in case-control study had prior exposure to gadolinium (Gd)-containing magnetic resonance imaging contrast agents); Centers for Disease Control, “Nephrogenic Fibrosing Dermopathy Associated with Exposure to Gadolinium-Containing Contrast Agents — St. Louis, Missouri, 2002–2006,” 56 MMWR Morbidity and Mortality Weekly Report (Feb. 23, 2007).

[2] T.A. Collidge, P.C. Thomson, P.B. Mark, et al., “Gadolinium-Enhanced MR Imaging and Nephrogenic Systemic Fibrosis: Retrospective Study of a Renal Replacement Therapy Cohort,” 245 Radiology 168-175 (2007); I.M. Wahba, E.L. Simpson, and K. White, “Gadolinium Is Not The Only Trigger For Nephrogenic Systemic Fibrosis: Insights From Two Cases And Review Of The Recent Literature,” 7 Am. J. Transplant. 1 (2007); A. Deng, D.B. Martin, et al., “Nephrogenic Systemic Fibrosis with a Spectrum of Clinical and Histopathological Presentation: A Disorder of Aberrant Dermal Remodeling,” 37 J. Cutan. Pathol. 204 (2009).