## Facts

- Hilary Davis, Srihari Munnuru, and Susan Fischer received a gadolinium-based contrast agent (GBCA) in connection with MRI scans.
- After GBCA exposure, each plaintiff reported developing chronic, multi-symptom health complaints (a broad range of symptoms rather than a single, well-defined disease).
- The plaintiffs filed three separate lawsuits in the District of Arizona against McKesson Corporation and various GBCA manufacturers and distributors, asserting product-liability and related tort claims under Arizona law.
- The court consolidated the three actions and sequenced the litigation to address general causation first—whether GBCAs are capable of causing the type of injuries plaintiffs claimed.
- Plaintiffs designated four retained experts to support causation, but the court found that none was qualified and reliable to opine that GBCAs can cause the plaintiffs’ wide constellation of symptoms; the court excluded the general-causation opinions under Federal Rule of Evidence 702 and Daubert.
- Regulatory and medical authorities that had reviewed GBCA safety, including the FDA, had not found sufficient scientific evidence to conclude that GBCAs cause the disease process alleged by plaintiffs.
- Following the exclusion of plaintiffs’ causation opinions, defendants moved for summary judgment, arguing that plaintiffs could not prove general causation, an element required for their claims.
- Plaintiffs responded that they could establish general causation through treating physicians’ testimony based on differential diagnoses (ruling out alternative causes for each plaintiff’s symptoms).

## Issues

1. Whether, after exclusion of plaintiffs’ retained causation opinions under Rule 702, plaintiffs could prove general causation for their alleged GBCA-related injuries through treating physicians’ differential-diagnosis testimony.
2. Whether summary judgment was required because plaintiffs lacked admissible evidence on general causation, an essential element of their Arizona-law claims.

## Decision

- The court granted defendants’ motions for summary judgment and ordered entry of judgment for all defendants, closing the consolidated cases.
- The court held that, without admissible expert evidence establishing general medical causation, plaintiffs could not carry their burden to show that GBCAs are capable of causing the broad set of symptoms they alleged.
- The court rejected plaintiffs’ attempt to rely on treating physicians and differential diagnoses to supply general causation, explaining that differential diagnosis addresses specific causation and does not prove that the agent can cause the condition in the general population.
- Because plaintiffs could not establish general causation, their tort and product-liability claims failed as a matter of law.

## Legal Principles

- In toxic-exposure and pharmaceutical cases involving medical and scientific questions beyond common experience, plaintiffs generally must present reliable expert testimony under Federal Rule of Evidence 702 and Daubert to prove general causation.
- Arizona causation analysis in this context requires proof of both (a) general causation (the substance is capable of causing the alleged injury) and (b) specific causation (it caused the plaintiff’s injury).
- Differential diagnosis is a patient-focused method aimed at identifying the likely cause of an individual’s symptoms; it presumes general causation and cannot substitute for scientific proof that the substance can cause the claimed condition.
- Treating-physician opinions do not fill a general-causation gap where the foundational general-causation theory is unsupported or has been excluded as unreliable.
- Under Federal Rule of Civil Procedure 56, summary judgment must be entered when the nonmoving party fails to produce evidence sufficient to prove an essential element on which it bears the burden at trial.

## Conclusion

In Davis v. McKesson Corporation, the District of Arizona entered summary judgment for GBCA manufacturers and distributors because plaintiffs, after their retained general-causation opinions were excluded under Rule 702 and Daubert, had no admissible evidence that GBCAs can cause the chronic, multi-symptom injuries they alleged, and treating physicians’ differential diagnoses could not establish general causation under Arizona law.


Davis v. McKesson Corporation, 2019 WL 5535376 (2019)