Objective Evidence of Anosmia

    An attorney who represented a 40 year old women who suffered a loss of sense of smell due to a head injury wrote me, concerned about whether or not a jury would believe it. He suggested that one can just fake anosmia, claiming not to smell anything when given a standard test of olfactory acuity. He asked if there is a definitive OBJECTIVE test to prove that one has anosmia. I conducted a quick Internet search and posted some queries to two discussion groups, one populated mostly by persons suffering from anosmia and another populated mostly by otorhinolaryngologists. Here I summarize what I found.


    My initial response to the attorney was:

    Your question is interesting, one I have not considered. My guess is that the medical community relies on the self-report of the afflicted person. Here are some of my thoughts, off the top of my head:

    When someone sues for emotional distress or pain and suffering, how does convince the jury? These are, IMHO, even more subjective.

    One could measure neural responses (in the brain) that accompany incoming olfactory signals. If presentation of olfactory stimuli did not produce such neural responses, then one would have objective confirmation of anosmia. Of course, such signals could be present but not properly processed in the brain, in which case the individual would still be anosmic.

    One can classically condition a reflexive response to a scent stimulus (most powerfully when the reflexive response is one associated with gastric distress). Evidence that such conditioning takes place in persons with normal olfaction but not in the afflicted person would convince me.

    Some scents produce a strong and easily observable response in most anybody who can smell them -- for example, the smell of vomit or the smell of skunk. Demonstrating that your client does not respond to such scents should be convincing, especially if you could get away with conducting such a response in the courtroom (but the judge might throw you and your scents out of the courthouse). You would need to be careful not to use a substance that would be expected to produce a response simply by irritating nasal tissues (ammonia, for example).

    I'll ask around and see if I can get any other suggestions.


    Thomas Hummel advised that by using olfactory evoked potentials one can easily ascertain the presence of anosmia. He pointed me to an abstract of an article by G. Kobal and T. Hummer -- Olfactory and intranasal trigeminal event-related potentials in anosmic patients, Laryngoscope, 1998, 108(7):1033-5. -- chemosensory event-related potentials (CSERPs) were not obtained in response to olfactory stimuli in anosmic patients, but they were obtained in response to stimulation of the nasal trigeminal nerve with carbon dioxide.


    I used Google to search for the phrase "chemosensory event-related potentials" and obtained 70 hits, including an article by Thomas Thesen and Claire Murphy -- Reliability analysis of event-related brain potentials to olfactory stimuli, Psychophysiology, 39, 2002, 733-738 -- which described the procedure -- it sounded like it involved fairly standard EEG procedures, recording potentials from the scalp while carefully presenting olfactory stimuli.


    I retrieved from our library an article by M. Levy and R. I. Henkin (Why should neuroradiologists study patients with smell loss, AJNR, American Journal of Neuroradiology, 2003, 24, 556-558), which addressed methods employed to verify that a person is anosmic. The authors mentioned psychophysical tests (such as determining absolute thresholds), but, of course, a jury might suspect that the plaintiff is faking those. The authors briefly discussed neuroradiological techniques including:

    This article is relatively easy reading, and includes 27 references to articles that are likely to have a lot more technical details.

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This page most recently revised on the 22nd of November, 2013.