Differential Diagnosis Methodology By Itself Insufficient To Establish Causation In Medical Malpractice Some medical events are hard to explain. Doctors use a methodology called "differential diagnosis" to come up with an explanation of medical events. "Differential diagnosis" essentially is a process of elimination where a doctor lists the likely causes of an event and then asks questions and performs tests to eliminate possibilities until he or she is satisfied that the single most likely cause has been identified. However, what if the single most likely cause identified is one which is not generally accepted by the scientific community. An interesting medical malpractice action from the First Department last week - Marso v Novak, 2007 NY Slip Op 06170 - answers this problem. In that case, the plaintiff suffered a bilateral stroke at the age of 43. Upon her admittance to the hospital, one of the first findings made by her treating physician, was that the plaintiff was suffering from bradycardia since her heart beat had slowed to 27 beats a minute. Subsequently, the treating physicians at the hospital became convinced that bradycardia was the only possible cause of the bilateral stroke, and that the stroke could have been prevented had the defendant, Dr. Novack, inserted a pacemaker in the year prior to plaintiff's stroke. The treating physician at the hospital, who was also plaintiff's expert witness on causation at trial, testified that all other possibilities for causation of the stroke were excluded by testing. He admitted, however, that it was not generally accepted in the scientific community that bradycardia is a risk factor for the type of embolic stroke suffered by plaintiff. The jury returned a verdict for the plaintiff. However, the defendants moved for a judgment notwithstanding the verdict on the grounds that the plaintiff had failed to present a prima facie case because her theory of causation (bradycardia caused the stroke) was not generally accepted in the scientific community. The trial court granted the defendant's motion and dismissed the case, and the First Department affirmed. The Court rejected the plaintiff's argument that since "differential diagnosis" was a generally accepted scientific methodology; its results should be sufficient to establish a prima facie case of causation. The Court noted that the plaintiff's own expert testified that bradycardia was not accepted by the scientific community as a cause of the type of stroke suffered by the plaintiff. And it reasoned that to accept a methodology-only approach would circumvent the rule of permitting before the jury only expert testimony which is based on generally accepted scientific principles. The Court also noted that it was the plaintiff's burden to show that his theory of causation was generally accepted by the scientific community, and in essence, the only thing that the plaintiff demonstrated was that the "differential diagnosis" methodology was generally accepted. And this simply was not enough.