Magnitude estimation measurements are important indicators of smell loss (hyposmia)
There are multiple methods to measure smell loss (hyposmia). Initially we used techniques similar to those used in hearing loss to identify smell loss. Thus, using three solutions only one of which has an odor and a range of 13 odor concentrations varying from very little to a great deal of odorant the patient detected and recognized the one solution containing the least amount of odorant or the threshold amount of odorant detected or recognized. This was the initial method we used to identify hyposmic patients. Using this technique it was possible to characterize the most dilute odorant solution detected and recognized by hyposmic patients. We compared these results with results obtained in normal subjects and identified hyposmic patients by their responses by which they chose a more concentrated solution of odorant than did normal subjects. These results allowed us to compare these higher detection thresholds and recognition thresholds (less sensitivity) for various odorants between hyposmic patients and normal subjects.
Overtime it became clear many patients with hyposmia did not always have significant problems with detection or recognition thresholds. These tests were not always sensitive enough to distinguish between hyposmic patients and normal subjects. A more sensitive measurement technique was required.
We then recognized that if hyposmic patients could determine odor intensity over the entire range of concentrations at which odorants were presented then this measurement was more useful and a more sensitive indicator of smell loss than a threshold measurement. We defined intensity measurements using a scale from 1-100 (or a penny to a dollar) with the more intense odor considered higher on the 1-100 scale and the less intense odor considered lower on the 1-100 scale. Thus, the highest or most intense odorant concentration detected or recognized was considered 100 with the least intense odorant concentration detected or recognized considered in the lower range of the 1 100 scale. The average odor intensity over the entire concentration range was calculated and a specific number, an average or mean, was calculated.
With this scale in place we could determine what is called “magnitude estimation” of a given odorant. This could be determined in addition to determining detection and recognition thresholds.
Results of this test were soon recognized to give specific information about the number of receptors functioning for any odorant. These results were much more sensitive to determine smell loss in hyposmic patients than threshold measurements.
We now consider results of magnitude estimation among the most useful results we obtain since we recognize that the receptor number present in the olfactory system is the most sensitive indicator of smell loss in hyposmic patients.
Thus, if the magnitude estimation of a given odorant is less than a mean value of 50 then it is clear, even if threshold values are normal, that the patient has hyposmia. If treatment increases smell function then this number increases to a mean value greater than 50 – the patient recognizes that smell function has improved and we can measure this improvement quantitatively by use of magnitude estimation.
For a detailed discussion of this method to determine smell loss, please see “Taste and smell function in chronic disease: A review of clinical and biochemical evaluation of taste and smell dysfunction in over 5000 patients at The Taste and Smell Clinic in Washington, DC” by R.I. Henkin, L.M. Levy and A. Fordyce, published by the American Journal of Otolaryngology, 34:477-489, 2013.