S055431, Opinion — Marcum v. Adventist Health System/West

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Argued and submitted June 4, decision of Court of Appeals reversed;
case remanded to Court of Appeals for further proceedings September 16, 2008

Deborah MARCUM,
Petitioner on Review,
v.
ADVENTIST HEALTH SYSTEM/WEST,
a foreign corporation,
dba Adventist Health;
Northwest Medical Foundation of Tillamook,
an Oregon corporation,
dba Tillamook County General Hospital;
Alliance Imaging, Inc.,
a foreign corporation;
Alliance Imaging Management, Inc.,
a foreign corporation;
and Alliance Imaging Centers, Inc.,
a foreign corporation,
Respondents on Review.
(CC 040505205; CA A129660; SC S055431)
193 P3d 1

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CJS, Evidence § 639.

# En Banc

On review from the Court of Appeals .*

Jeffrey B. Wihtol, Portland, argued the cause and filed the
brief for petitioner on review.

Janet M. Schroer, Hoffman Hart & Wagner, LLP,
Portland, and Lisa E. Lear, Bullivant Houser Bailey, P.C.,
Portland, argued the cause and filed the brief for respondents
on review. With them on the brief was Marjorie A. Speirs,
Hoffman Hart & Wagner, LLP, Portland.

Linda K. Eyerman, Gaylord Eyerman Bradley, P.C.,
Portland, filed the brief for amicus curiae Oregon Trial
Lawyers Association. With her on the brief was Leslie W.
O'Leary, Williams Love O'Leary & Powers, Portland.

BALMER, J.

The decision of the Court of Appeals is reversed. The case
is remanded to the Court of Appeals for further proceedings.

\* Appeal from Multnomah County Circuit Court, George A. Van Hoomissen,
Senior Judge. 215 Or App 166, 168 P3d 1214 (2007).

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Cite as 345 Or 237 (2008)

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# BALMER, J.

This medical malpractice action requires us to
review and apply the standards for admission of expert med-
ical testimony. Under the applicable evidentiary rules, as
interpreted in this court's cases, an expert's medical testi-
mony must meet a test of "scientific validity." Plaintiff here
experienced symptoms of pain, swelling, and discoloration in
her left hand immediately after injection of a chemical called
gadolinium; her pain and the discoloration have continued.
At trial, plaintiff proffered the testimony of a medical expert
that the gadolinium, instead of going into the vein, went into
an area of her hand outside the vein, a circumstance known
as "extravasation." As a result, according to the expert, the
toxicity of the gadolinium caused both her immediate and her
ongoing symptoms. Defendants objected to the expert's prof-
fered testimony, and the trial court ruled that the testimony
did not meet the legal standard for scientific validity. The
Court of Appeals affirmed. Marcum v. Adventist Health
System / West, 215 Or App 166, 168 P3d 1214 (2007). We
granted review and now reverse.

The Court of Appeals described the facts and the pro-
cedural background of the case:

"In March 2003, after plaintiff was involved in an auto acci-
dent, suffering a possible head injury, her doctor ordered an
MRI. Plaintiff went to Tillamook County General Hospital
and was escorted to an MRI trailer just outside. The MRI
technologist, employed by Alliance, informed plaintiff that
he would be injecting her with a contrast chemical, gadolin-
ium, used to enhance the MRI image.

"Alliance's MRI technologists are trained to advise
patients that, if the injection of a contrast chemical causes
pain or any other discomfort, they should immediately
inform the technologist. If a patient makes such a com-
plaint, the technologists are trained to check for extravasa-
tion. 'Extravasation' occurs when a substance exits the vein
and enters the surrounding tissue. See Stedman's Medical
Dictionary 635 (27th ed 2000) (defining 'extravasate' as,
inter alia, '[t]o exude from or pass out of a vessel into the tis-
sues'). The general standard of care applicable to MRI tech-
nologists requires that they explain the procedure to the
patient and ask the patient to inform them if they feel pain.

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However, neither plaintiff's technologist nor her treating
physician explained the injection procedure, asked her to
report pain, or explained to her any risks associated with
the injection.

"After attempting the injection on each of plaintiff's
arms unsuccessfully, the technologist attempted to make
the injection on the back of plaintiff's left hand. Immedi-
ately after the needle went into her hand, plaintiff com-
plained that her hand felt 'like a glove filling up.' She
explained to the technologist that 'if he was to take the tip of
my fingers off he would see the stuff running on the floor.
That's how full it felt.' The technologist acknowledged
plaintiff's complaint but told her it would be okay and fin-
ished the procedure.

"Plaintiff manages a restaurant. She normally performs
various functions in the business, including food prepara-
tion, which involves going to the restaurant's walk-in
refrigerator. The day after the MRI, however, when she
went to the walk-in refrigerator she had a difficult time
handling the cold food and complained that her left hand
hurt. Her coworker described her hand as appearing pur-
ple, orange, and swollen. After a couple of hours, plaintiff
went to the emergency room. She has experienced pain ever
since, which has impaired her ability to work. Plaintiff's
hand has remained discolored near where she received the
gadolinium injection.

"Plaintiff filed this action against defendants. In her
operative complaint, she alleged that defendants had neg-
ligently injured her and negligently failed to obtain her
informed consent before injecting her with gadolinium.

"[A]t trial, the court excluded portions of the testimony
of plaintiff's two expert witnesses, Dr. Weldon Williamson
and Karen Marburger. Williamson, a medical doctor spe-
cializing in hand disorders, would have testified concerning
medical causation. Marburger, an MRI technologist, would
have testified that defendants should have made and kept
various records and that, had plaintiff been able to obtain
those records, they might have been beneficial in proving
plaintiff's claims.

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"With respect to Williamson's testimony, the court held
an OEC 104 hearing to determine whether Williamson's
opinion regarding causation-specifically that gadolinium
extravasation caused plaintiff's [vasospastic disorder1]-
was 'scientifically valid' under the standards prescribed in
[State v.] Brown[, 297 Or 404, 687 P2d 751 (1984)] and
[State v.] O'Key[, 321 Or 285, 899 P2d 663 (1995)]. The court
ultimately concluded that that testimony did not satisfy the
requisites of foundational admissibility. * * *

"Defendants moved for a directed verdict on plaintiff's
medical negligence claim based on plaintiff's failure to pro-
duce evidence of causation. Plaintiff, while maintaining
that the exclusion of Williamson's testimony was error,
agreed that without that testimony, she had not produced
evidence of causation. * * * The court directed a verdict in
defendants' favor * * * and entered judgment accordingly."

Marcum, 215 Or App at 169-72.

Plaintiff appealed, and the Court of Appeals
affirmed. The central issue on appeal was whether the testi-
mony of plaintiff's expert as to the likely cause of plaintiff's
injury met the test of scientific validity.2 The Court of
Appeals reasoned that the expert had failed to identify a sci-
entifically valid cause of the injury-one that linked plain-
tiff's exposure to gadolinium to the vasospastic disorder that
she experienced. In particular, the court noted that the
expert had failed to show, either through studies showing a
high degree of correlation between gadolinium exposure and
the kind of injury that plaintiff had suffered or through a sci-
entifically demonstrable mechanism of causation, that the

1 The parties sometimes refer to plaintiff's condition as "vasospasm," "digital
artery disease," or as "similar" to Raynaud's syndrome, a condition in which an
artery "clamps down" abnormally in response to cold. It is undisputed that plaintiff
suffered some kind of immediate injury to her hand at the time of the injection and
that she continued to experience symptoms of vasospastic disorder.

2 The parties do not dispute the professional qualifications of plaintiff's expert,
Williamson, who is a vascular surgeon and a member of the Department of
Vascular Surgery at Oregon Health and Sciences University. Williamson is an
expert on the treatment of vascular impairment to the hands and fingers and has
done substantial research in the area and published book chapters and journal
articles on that subject. He is also the author of a chapter in a 1998 medical text-
book on the methodology for differentiating the causes of vascular problems in the
hand and fingers. The parties also do not disagree as to Williamson's diagnosis of
plaintiff's condition. The sole dispute concerns his testimony as to the cause of
plaintiff's condition and whether his expertise permits an opinion as to that cause.

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gadolinium extravasation could have caused plaintiff's vaso-
spastic disorder. Id. at 184-88. Judge Armstrong dissented.
While conceding that the issue was a close one, he thought
that the expert's testimony was sufficiently scientific in
nature and helpful to the trier of fact to warrant its admis-
sion. Id. at 193-98 (Armstrong, J., concurring in part, dis-
senting in part).3

We begin by reviewing the standards that this court
has used to determine whether scientific evidence will be
admitted. In Jennings v. Baxter Healthcare Corp., 331 Or
285, 301, 14 P3d 596 (2000), the court noted that its prior
cases had held that expert testimony is admissible if it is rel-
evant under OEC 401,4 would assist the trier of fact under
OEC 702,5 and is not subject to exclusion under OEC 4036
because its probative value is outweighed by the danger of
unfair prejudice or jury confusion. In this case, as in many
others involving the admissibility of scientific evidence, we
must determine "'whether scientific evidence is probative
under OEC 401'" and conduct the " 'relevancy and prejudice
analysis implicated in OEC 702's helpfulness standard[.]'"
Jennings, 331 Or at 302 (quoting Brown, 297 Or at 417); see
also Brown, 297 Or at 409 (court must "identify and evaluate
the probative value of the evidence, consider how it might
impair rather than help the factfinder, and decide whether
truthfinding is better served by exclusion or admission").

3 The Court of Appeals also rejected two assignments of error related to the
alleged spoliation of evidence. Plaintiff did not petition for review of those issues,
and we do not consider them.

4 OEC 401 provides:

" 'Relevant evidence' means evidence having any tendency to make the
existence of any fact that is of consequence to the determination of the action
more probable or less probable than it would be without the evidence."

5 OEC 702 provides:

"If scientific, technical or other specialized knowledge will assist the trier
of fact to understand the evidence or to determine a fact in issue, a witness
qualified as an expert by knowledge, skill, experience, training or education
may testify thereto in the form of an opinion or otherwise."

6 OEC 403 provides:

"Although relevant, evidence may be excluded if its probative value is sub-
stantially outweighed by the danger of unfair prejudice, confusion of the
issues, or misleading the jury, or by considerations of undue delay or needless
presentation of cumulative evidence."

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In O'Key, 321 Or at 291, this court explained the
principles underlying the application of the evidentiary rules
to scientific evidence:

"Evidence perceived by lay jurors to be scientific in
nature possesses an unusually high degree of persuasive
power. The function of the court is to ensure that the per-
suasive appeal is legitimate. The value of proffered expert
scientific testimony critically depends on the scientific
validity of the general propositions utilized by the expert."

(Footnote omitted.) In ruling on admissibility, the trial court
performs the "vital role" of "gatekeeper," id. at 307, screening
proffered scientific testimony to determine whether it is suf-
ficiently valid, as a matter of science, to legitimately assist
the trier of fact and "exclud[ing] 'bad science' in order to con-
trol the flow of confusing, misleading, erroneous, prejudicial,
or useless information to the trier of fact." Id. at 306.

This court has set out a number of factors that may
be considered in determining the admissibility of scientific
evidence:

"(1) The technique's general acceptance in the field;

"(2) The expert's qualifications and stature;

"(3) The use which has been made of the technique;

"(4) The potential rate of error;

"(5) The existence of specialized literature;

"(6) The novelty of the invention [if one is involved]; and

"(7) The extent to which the technique relies on the sub-
jective interpretation of the expert."7

7 To that list, the court joined 11 additional considerations:

"(1) The potential error rate in using the technique;

"(2) The existence and maintenance of standards governing its use;

"(3) Presence of safeguards in the characteristics of the technique;

"(4) Analogy to other scientific techniques whose results are admissible;

"(5) The extent to which the technique has been accepted by scientists in
the field involved;

"(6) The nature and breadth of the inference adduced;

"(7) The clarity and simplicity with which the technique can be described
and its results explained;

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Brown, 297 Or at 417. Those factors, however, are not an
"exclusive checklist," Jennings, 331 Or at 302, and the " 'exis-
tence or nonexistence'" of any particular factor may enter
into the final decision on admissibility, " 'but need not neces-
sarily do so.'" Id. at 303 (quoting Brown, 297 Or at 417-18).
Underlying the various considerations and factors described
by the court is the fundamental question of the "'scientific
validity of the general propositions utilized by the expert.'"
Jennings, 331 Or at 303 (quoting O'Key, 321 Or at 291).

This court has applied the foregoing principles to
determine the admissibility of scientific evidence in several
cases. The parties discuss in detail this court's decisions in
Brown, where the court considered the admissibility of poly-
graph evidence, and O'Key, where the court evaluated the
admissibility of the Horizontal Gaze Nystagmus (HGN) test
as a preliminary method of determining whether a defendant
might be under the influence of intoxicants. As the citations
to those cases in the discussion above shows, the cases are
helpful in the sense that they describe the general rules for
admissibility of scientific evidence. However, they provide
limited guidance in deciding the issue before us, because both
Brown and O'Key involved the admissibility of specific tech-
niques or tests, the validity of which turned on scientific prin-
ciples.8 Here, in contrast, the expert testimony at issue
focuses on medical causation-specifically, whether plain-
tiff's injuries were caused by the gadolinium that was

"(8) The extent to which the basic data are verifiable by the court and
jury;

"(9) The availability of other experts to test and evaluate the technique;

"(10) The probative significance of the evidence in the circumstances of
the case; and

"(11) The care with which the technique was employed in the case."
Brown, 297 Or at 417-18 n 5.

" For that reason, the court in Brown phrased many of the factors to be consid-
ered in determining admissibility with reference to the "technique" of polygraph
analysis-whether the "technique" was generally accepted in the field, the poten-
tial error for the "technique," and so on. Brown, 297 Or at 417, 417 n 5. Similarly,
the court in O'Key consistently phrased the standard for admissibility and its appli-
cation of that standard as whether the HGN "test" was generally accepted and was
the subject of specialized scientific literature, among other considerations. O'Key,
321 Or at 306, 314-19 (stating and applying standard).

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injected into her hand-and the question is whether the prof-
fered expert testimony about causation meets the standard of
scientific validity. That is, the issue is the scientific basis for
the causation testimony, rather than the scientific basis for a
particular technique or method.

This court considered the admissibility of expert
medical testimony as to causation in Jennings. There, the
plaintiff proffered expert testimony that her neurological
problems were caused by silicone that had leaked from sili-
cone breast implants. The expert had examined approxi-
mately 50 women, many of whom had inner-ear balance
problems and loss of sensation in their extremities after
exposure to silicone. The expert testified that "the unique
thing was that there was an extraordinarily high correlation,
95 percent had the combination of unusual sensory patterns
and the inner ear [problem]." 331 Or at 290 (emphasis omit-
ted). As part of his analysis, the expert performed a "differ-
ential diagnosis," in which he considered various potential
causes of the symptoms and then ruled out all but one, the
exposure to silicone. Id. at 291 ("In a differential diagnosis, a
doctor develops a list of all diseases that might cause a
patient's symptoms and then, by a process of elimination,
narrows the list."). Although no published studies, peer-
reviewed publications, or medical consensus supported his
testimony as to causation, id. at 292-93, this court held that
the testimony should have been admitted. "Although [the
expert's] hypothesis has not been tested by others, that is, in
part, because his work is new." Id. at 307.

Two aspects of Jennings are pertinent to this case.
First, this court expressly permitted the use of "differential
diagnosis" as a means of determining medical causation. Sec-
ond, the court concluded that OEC 702 does not automati-
cally preclude the admission of "novel" scientific evidence: "If
it is otherwise scientifically valid, a novel conclusion is
admissible." 331 Or at 307. Thus, although published studies
and acceptance of the theory in the medical community are
relevant considerations, their absence in that case did not
mean that the expert's scientific testimony as to causation
had to be excluded. The expert in Jennings could not explain
the mechanism by which silicone had caused the neurological
problems, but he reported a high correlation between expo-
sure to silicone and the specific neurological symptoms in the

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women whom he had studied. From that correlation and the
elimination of other possible causes of the symptoms, the
expert reached the conclusion that the exposure to silicone
had been the likely cause of the plaintiff's symptoms. This
court concluded that the expert testimony on causation was
scientifically valid and should have been admitted. 331 Or at
305.

We turn to the application of those principles to the
expert testimony here. As noted, in Jennings, this court rec-
ognized that "differential diagnosis"9 is an accepted tech-
nique in which "a doctor develops a list of all diseases that
might cause a patient's symptoms and then, by a process of
elimination, narrows the list." 331 Or at 291 (citing Mary Sue
Henifin, Howard M. Kipen, and Susan R. Poulter, Reference
Guide on Medical Testimony, in Reference Manual on
Scientific Evidence 439, 463 (Federal Judicial Center ed., 2d
ed 2000)). Put differently, differential diagnosis involves a
process by which a medical expert first "rules in" various
potential causes and then "rules out" those causes one by one
(to the extent possible) by analyzing the patient's condition
until the expert can identify the likely cause from among
those remaining. Thus, "differential diagnosis" is a general
description of a methodology or process accepted by the med-
ical community as a means of determining causation (or con-
dition), rather than a specific scientific technique or test,
such as the HGN test considered in O'Key or the use of poly-
merase chain reaction-based DNA testing at issue in State v.
Lyons, 324 Or 256, 924 P2d 802 (1996). For that reason,
although differential diagnosis can be the basis for admissi-
ble expert testimony as to medical causation, testimony is not

9 We recognize, as did the Court of Appeals, Marcum v. Adventist Health
System / West, 215 Or App 166, 175 n 5, 168 P3d 1214 (2007), that the term "differ-
ential diagnosis" is more properly used to describe the process of determining the
disease or symptoms from which a patient is suffering, rather than the process of
determining the external cause of the disease or symptoms, and that "differential
etiology" is a more precise description of the latter. See Mary Sue Henifin, Howard
M. Kipen, and Susan R. Poulter, Reference Guide on Medical Testimony, in
Reference Manual on Scientific Evidence 439, 481 (Federal Judicial Center ed., 2d
ed 2000) (defining those terms). However, given the widespread use of the term
"differential diagnosis" to apply to determinations of causation as well as of disease
or symptoms, we use that term here. Further, we reject defendants' argument that
Williamson lacks expertise in "differential etiology." We need not decide whether,
as plaintiffs argue, all doctors have expertise in differential etiology as well as dif-
ferential diagnosis. It is sufficient in this case to say that Williamson had expertise
in the causation of vascular disorders of the extremities.

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admissible simply because the expert conducted a differen-
tial diagnosis. Rather, admissibility will turn on whether the
particular use of differential diagnosis to determine causa-
tion meets the more general test of scientific validity. See
Jennings, 331 Or at 305-10 (concluding, after reviewing
expert's basis for including and excluding potential causes of
plaintiff's condition, that differential diagnosis provided suf-
ficient basis for expert to testify that silicone exposure was
likely cause of the plaintiff's condition).

We also recognize, as did the Court of Appeals, that
differential diagnosis of medical causation often cannot lead
an expert to conclude, with certainty, that event "A" caused
condition "B."10 Rather, in many cases, a number of potential
causes will be "ruled in," each of which has some percentage
of likelihood of having caused plaintiff's condition; then the
expert, by physical examination, testing, or other scientifi-
cally valid process, eliminates one or more of the potential
causes in an effort to identify the actual cause. Even if the
expert is not able to eliminate all alternative causes, the tes-
timony nevertheless may be reliable and admissible if suffi-
cient potential causes are eliminated for the expert to iden-
tify one particular cause as the likely cause of the condition.
See Note, Navigating Uncertainty: Gatekeeping in the
Absence of Hard Science, 113 Harv L Rev 1467, 1474 (2000)
(courts generally allow admission of differential diagnosis
even when technique has not eliminated all alternative
causes).

Moreover, the basis for establishing the scientific
validity of a differential diagnosis will vary depending on the
type of injury. In the typical toxic tort case, there may be "a
complicated causal chain, a long latency period, or low levels
of exposure * * *. " Note, 113 Harv L Rev at 1472. In those cir-
cumstances, reliable testimony on causation may require
"extremely accurate data and methods," peer-reviewed stud-
ies, and small and controlled error rates to "rule in" a possible
cause. Id .; see also id. at 1480 ("[O]ther characteristics of the

10 Of course, expert testimony of causation is sufficient if it establishes that
defendant's conduct was the likely cause of plaintiff's injury; certainty is not
required. See Joshi v. Providence Health System, 342 Or 152, 159, 149 P3d 1164
(2006) (causation in wrongful death action requires proof that defendant's acts or
omissions "more likely than not" caused plaintiff's injuries).

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generic toxic tort-a long latency period, complicated biolog-
ical explanation, and lack of a single sharp exposure event-
are likely to make alternative causes seem both substantially
probable and difficult to exclude."). In contrast, when the
exposure occurs in a single, sharp event, and the injury is
immediate and localized, it may be appropriate to "rule in"
the exposure as one of the possible causes of the injury, par-
ticularly when there are few obvious alternative causes. Id.
at 1473 (describing circumstances in which toxic exposure
may be considered as cause of plaintiff's injuries, even in the
absence of epidemiological studies). Of course, when "ruling
in" potential causes of a condition or injury for purposes of
differential diagnosis, a trial court should insist that the cau-
sation theory be "biologically plausible," that is, that the
exposure could have caused plaintiff's injury. Id. at 1475 (cit-
ing Reference Manual on Scientific Evidence at 163, 204);
see also Jennings, 331 Or at 309 (" 'What is biologically plau-
sible depends upon the biological knowledge of the day.'"
(Quoting Hill, The Environment and Disease: Association or
Causation?, 58 Proc R Soc Med 295, 298 (1965).)). For that
reason, a particular possible cause should not necessarily be
excluded on the grounds that the expert cannot describe the
precise mechanism of causation or point to statistical studies
of cause and effect. See Jennings, 331 Or at 309 ("There are
many generally accepted hypotheses in science for which the
mechanism of cause and effect is not understood fully.").

In this case, the Court of Appeals accepted the con-
cept of differential diagnosis but concluded that there was no
scientific basis for plaintiff's expert to "rule in" gadolinium
exposure as a possible cause of plaintiff's symptoms.
Marcum, 215 Or App at 181-82, 187. The court reached that
conclusion because, in its view, the expert's testimony did not
meet the standard required for scientific validity:

"Either the expert must be able to identify a scientifically
demonstrable mechanism of causation or there must be
some independent, verifiable corroboration of otherwise
inexplicable causation, as in Jennings. Where, however, a
plaintiff's circumstances are unique and the expert cannot
proffer a mechanism of causation, general temporal and
spatial proximity to the onset of symptoms, even when cou-
pled with reports of other adverse effects, is insufficient."

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Id. at 187. Because there was no basis to "rule in" gadolinium
extravasation as a cause of plaintiff's injuries, the court rea-
soned, the expert's elimination of other potential causes and
his subsequent conclusion that gadolinium extravasation
likely had caused the injuries was inadmissible. Id.

In reaching that conclusion, the Court of Appeals
cited the appropriate tests identified in Brown, O'Key, and
Jennings, but we think that it applied them in too rigorous a
manner, given the context of this case. The court seemed to
suggest that, in the absence of a well-understood mechanism
of causation or a study demonstrating a high correlation
between exposure and injury, testimony as to causation is not
permitted because the possible cause never could be "ruled
in" for purposes of a differential diagnosis.

In Jennings, however, this court concluded that the
expert's inability to explain the mechanism of plaintiff's con-
dition in that case went to the weight, not to the admissibi-
lity, of the evidence. 331 Or at 309. And, although plaintiff's
expert here could not point to studies demonstrating a corre-
lation between gadolinium extravasation and vasospastic
disorder in the hand, our discussion above of the use of differ-
ential diagnosis shows that the absence of such studies does
not necessarily preclude "ruling in" that exposure as a possi-
ble cause of plaintiff's injuries. With that discussion in mind,
we return to the expert testimony at issue here.

Plaintiff's expert identified a number of reasons that
he "ruled in" gadolinium extravasation as a potential cause
of plaintiff's vasospastic disorder: Her symptoms occurred
almost immediately after the injection and in the same area
as the injection. Her description of her sensations during the
injection was consistent with extravasation, and she had no
symptoms prior to the injection. Published medical literature
suggested that gadolinium exposure can be toxic to tissue in
mice, that it can cause inflammation and necrosis (tissue
death), and that those toxic effects are likely increased by
extravasation because the body has greater difficulty excret-
ing a substance when it is located outside the arterial system.
Although plaintiff's expert did not diagnose necrosis in plain-
tiff's hand, he testified that plaintiff may have necrosis under
the skin. The expert also testified that no studies existed

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linking gadolinium to vasospastic disorder and that no stud-
ies were likely to be done because gadolinium extravasation
is rare, and particularly so in the hand, as contrast chemicals
used in MRI examinations ordinarily are not injected into the
hand.

Plaintiff's expert also testified as to the scientific
reasons that he "ruled out" other possible causes of plaintiff's
symptoms. Notably, he ruled out an ordinary case of
Raynaud's syndrome itself, because that syndrome almost
always appears in both hands (bilaterally), while plaintiff's
symptoms manifested themselves only in the hand where the
injection had occurred. Through blood tests and other
diagnoses, he ruled out other potential causes of plaintiff's
symptoms, including connective tissue and autoimmune dis-
orders, such as lupus. He also ruled out allergic or hyper-
sensitivity reactions to the gadolinium. Based on his
research, examination, and tests, plaintiff's expert concluded
that plaintiff's symptoms probably were caused by gadolin-
ium extravasation.

As noted, after reviewing that proffered testimony,
the Court of Appeals concluded that it lacked scientific
validity because the expert was unable to "identify a scientif-
ically demonstrable mechanism of causation" or provide
"some independent, verifiable corroboration of otherwise
inexplicable causation[.]" Marcum, 215 Or App at 187. A brief
discussion of the court's reasoning demonstrates why we con-
clude that it took too narrow a view in considering the scien-
tific validity of that testimony. First, as to the "mechanism of
causation" standard, plaintiff's expert testified that the cause
of Raynaud's syndrome (vasospastic disorder) has not been
established in the medical community-that is, the condition
can be identified, but its mechanism of causation is
unknown.11 He also testified that there was nothing in the
medical literature to suggest that gadolinium could not
cause plaintiff's symptoms. See Jennings, 331 Or at 309
(expert's opinion as to causation had not been accepted by the

11 Although the Court of Appeals viewed that fact as a critical reason not to
"rule in" gadolinium exposure as a possible cause of plaintiff's symptoms, that fact
had to be weighed with the other grounds that the expert gave for "ruling in" that
exposure. It is the combination of facts that we review.

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scientific community, but neither had it been rejected).
Finally, the expert pointed to tests on mice that showed that
the injection of gadolinium was toxic to tissue, causing
inflammation and necrosis. He further explained that the
studies showed that the toxicity was related to the duration
of exposure and that the extravasation would have made the
gadolinium more toxic to plaintiff because it would have
remained in her system longer than if it had been properly
injected.

Second, the Court of Appeals certainly was correct in
noting that "independent, verifiable corroboration" can be
critical in demonstrating "otherwise inexplicable causation."
Marcum, 215 Or App at 187. However, injuries may be rare
or unique, as plaintiff's injury was here, and, for that reason
or because of ethical or other considerations, studies and
comparisons may not be possible. As discussed above, if other
legitimate grounds for "ruling in" a potential cause exist, as
they do here, then the absence of corroboration is not, itself,
necessarily grounds for exclusion.

It follows from the foregoing that, by focusing nar-
rowly on the absence of a scientifically accepted mechanism
of causation or other verifiable correlation, the Court of
Appeals asked for too much. More specifically, the court dis-
regarded the potential connection between the gadolinium
extravasation and plaintiff's injuries, because, in that court's
view, that potential cause could not be "ruled in." Although
the court was properly concerned with avoiding the logical
fallacy of post hoc, ergo propter hoc (after this, therefore
because of this) reasoning, it failed to give appropriate defer-
ence to the expert witness's reliance upon plaintiff's sudden,
single exposure and her immediate, localized symptoms, as
well as to the biological plausibility of the expert's causation
theory. The immediate symptoms that plaintiff experienced
in her hand indicate a causal link between the exposure and
her symptoms, and her expert's careful differential diagnosis
supports that connection. Moreover, the expert's reliance on
studies demonstrating the toxicity of gadolinium provide a
biologically plausible basis for his conclusion. Applying the
criteria identified above, we agree with plaintiff that she had
made an adequate showing of a scientifically valid basis for
"ruling in" gadolinium as a potential cause of her symptoms,

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as well as for "ruling out" a number of the other possible
causes of her injury. The jury should have been permitted to
hear the expert's testimony that, in his opinion, the gadolin-
ium extravasation caused that injury.

Defendants argue that permitting plaintiff's expert
to offer his opinion as to causation in the absence of a scien-
tifically demonstrable mechanism of causation or studies
demonstrating a high degree of correlation between cause
and effect undermines this court's emphasis on the require-
ment of scientifically valid expert testimony. In particular,
they imply that such a decision would permit experts to spec-
ulate on the causal connection between even brief exposure to
toxic substances and later physical symptoms. That concern
is misplaced. Here, the exposure event was direct and abrupt,
and the symptoms were immediate and localized. In those
circumstances, and given the acknowledged expertise and
skill of plaintiff's medical witness, his reliance on the tempo-
ral and spatial relationships between the exposure and the
symptoms (along with the other facts described above) and
the biological plausibility of his conclusion as to causation
support the scientific validity of his testimony. See generally
Note, 113 Harv L Rev at 1484 (significance of differential
diagnosis and temporal proximity is inherently contextual
and depends on sharpness of exposure event, among other
things).

The testimony of plaintiff's expert should have been
admitted. Questions as to the weight to be given that testi-
mony, possible weaknesses in the expert's theory, and the
ultimate issue of causation were for the jury to decide based
on all the evidence.

Based on its decision regarding Williamson's testi-
mony, the Court of Appeals affirmed the trial court's directed
verdict on plaintiff's negligence claim and on her informed
consent claim. Our disposition of the evidentiary issue means
that we reverse the lower court rulings with respect to the
negligence claim. Defendants, however, advanced alterna-
tive arguments before the Court of Appeals as to why the
directed verdict on the informed consent claim was proper.
The Court of Appeals has not considered those arguments,

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and we therefore remand to that court so that it may consider
them.

The decision of the Court of Appeals is reversed. The
case is remanded to the Court of Appeals for further
proceedings.