A federal appeals court has reinstated a suit in which a Tennessee plaintiff alleged his exposure to a pool cleaner caused him to lose his sense of smell. The 6th Circuit found that the trial court had improperly excluded his medical expert from testifying. Best v. Lowe’s Home Centers Inc., 2009 WL 1010883 (6th Cir.  4/16/09).

Of great interest to readers of MassTortDefense is the court’s treatment of the concept of differential diagnosis. This diagnostic method has long been used by treating physicians to assess what ails a patient, and it involves a logical process of ruling in and ruling out possible diagnoses based on symptoms, test results, and other medical evidence. The process has been hijacked by plaintiff experts to offer an aura of reliability to opinions not only about the diagnosed injury, but the cause of the injury. Plaintiff experts may make no effort to establish why a cause is even on the list to be ruled out (assuming general causation), and may rule out potential alternative causes with far less rigor than doctors would exclude alternative diagnoses in the real world.

Plaintiff in Best claimed to suffer from permanent loss of his sense of smell as a result of a pool chemical spilling onto his face and clothing at a Lowe’s Home Center store. Best planned to introduce the expert testimony of Dr. Francisco Moreno, a board-certified otolaryngologist, in order to establish the causal link between the chemical spill and his injuries. The district court excluded Dr. Moreno’s testimony, holding that the method employed by the doctor in drawing his conclusions regarding causation was “unscientific speculation.” This resulted in summary judgment.

In summary, because of the temporal relationship between Best’s exposure to the chemical and the onset of his symptoms, in conjunction with an effort to eliminate other possible causes of anosmia, Dr. Moreno formed the opinion that the inhalation of the Aqua EZ caused Best to lose his sense of smell. The 6th Circuit stated that Dr. Moreno thus employed a “differential diagnosis” methodology in forming his opinion. Differential diagnosis is, according to the court, the method by which a physician determines what disease process caused a patient’s symptoms. The physician considers all relevant potential causes of the symptoms and then eliminates alternative causes based on a physical examination, clinical tests, and a thorough case history. Hardyman v. Norfolk & W. Ry. Co., 243 F.3d 255, 260 (6th Cir.2001). The court was less than precise in its treatment of the slippery slope between causation of symptoms (what disease is causing the symptoms) to causation of disease (what toxic exposure caused the disease that caused the symptoms).

Dr. Moreno formed his opinion regarding Best’s alleged loss of his sense of smell by considering a list of the possible causes of such an injury, including virus, accident, tumor, surgery, or exposure to chemicals, as well as Best’s use of medications. He noted that the chemical was quite concentrated, and relied on Best’s report that the material splashed onto his face and clothing. Dr. Moreno ruled out medications as the cause, based on his knowledge of the side effects.

The 6th Circuit said it recognizes differential diagnosis as an appropriate method for making a determination of causation for an individual instance of disease. Differential diagnosis is considered to be “a standard scientific technique of identifying the cause of a medical problem by eliminating the likely causes until the most probable one is isolated.” Hardyman, 243 F.3d at 260 (quoting Westberry, 178 F.3d at 262).

But the court did note that not every opinion that is reached via a differential-diagnosis method will meet the standard of reliability required by Daubert. To determine which opinions do and do not, the court adopted the reasoning of the Third Circuit in In re Paoli Railroad Yard PCB Litigation, 35 F.3d 717 (3d Cir.1994).  A medical causation opinion in the form of a doctor’s differential diagnosis is reliable and admissible where the doctor (1) objectively ascertains, to the extent possible, the nature of the patient’s injury, (2) “rules in” one or more causes of the injury using a valid methodology, and (3) engages in standard diagnostic techniques by which doctors normally rule out alternative causes to reach a conclusion as to which cause is most likely. In connection with the third “rules out” prong, if the doctor engages in very few standard diagnostic techniques by which doctors normally rule out alternative causes, the doctor must offer a good explanation as to why his or her conclusion remains reliable. Similarly, the doctor must provide a reasonable explanation as to why he or she has concluded that any alternative cause suggested by the defense was not the sole cause.