Prevalence and correlates of parosmia and phantosmia among smell disorders

Abstract

Among those many individuals who experience a reduced odor sensitivity (hyposmia/anosmia) some individuals also have disorders that lead to odor distortion, such as parosmia (i.e., distorted odor with a known source), or odor phantoms (i.e., odor sensation without an odor source). We surveyed a large population with at least one olfactory disorder (N = 2031) and found that odor distortions were common (46%), with respondents reporting either parosmia (19%), phantosmia (11%), or both (16%). In comparison to respondents with hyposmia or anosmia, respondents with parosmia were more likely to be female, young, and suffering from post-viral olfactory loss (p < 0.001), while respondents with phantosmia were more likely to be middle-aged (p < 0.01) and experiencing symptoms caused by head trauma (p < 0.01). In addition, parosmia, compared to phantosmia or anosmia/hyposmia, was most prevalent 3 months to a year after olfactory symptom onset (p < 0.001), which coincides with the timeline of physiological recovery. Finally, we observed that the frequency and duration of distortions negatively affects quality of life, with parosmia showing a higher range of severity than phantosmia (p < 0.001). Previous research often grouped these distortions together, but our results show that they have distinct patterns of demographics, medical history, and loss in quality of life.

Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19 related olfactory disorders

“…This finding supports reports of individuals with parosmia often finding odors to be unpleasant (39). However, less commonly, some patient reports have shown a valence flip - in addition to pleasant odors smelling unpleasant, reporting odors typically experienced as foul are now pleasant (31,53,54). To test this valence flip theory, an actual unpleasant target odor may need to be experienced to capture the less-common negative-to-positive hedonic experience as our use of an imagined unpleasant odor was not adequate.…”

“…The intensity subtest had a cut-off of 20 (out of 100) when calculating SCENTinel 1.1 overall score, but was analyzed as a continuous measure (0-100) in the Bayes analysis and prediction model (described below) to benefit from the full-scale variability of the ratings. This design, in accordance with the preregistration (48), originally included a “mixed” group in the between-subject factor smell ability (Figure 1), but this group showed no coherent pattern (similar to a recent study (31)) and was therefore removed from the main analysis (see Supplementary Table 2). Demographics included in the analyses were sex (male, female), race (white, non-white), and age (continuous).…”

“…Of those who contract COVID-19, about 50% self-report losing their sense of smell (7). While most of these individuals fully recover their sense of smell within three weeks (8)(9)(10)(11), through interviews (30)(31)(32)(33)(34)(35). This reliance on self-report leaves estimates of qualitative olfactory disorders likely underrepresented, only diagnosed when individuals consult specialists.…”

“…Directly testing for parosmia may still prove difficult, because parosmia reports are not consistent across all odors. Odors that are frequently associated with parosmia include coffee, meats, onion, garlic, and chocolate (2,31,40), yet the direct cause for the odor-specificity remains to be understood. Individuals with odor-specific parosmia may only be detected with direct smell tests if the distorted odor is used in the test, and therefore, multiple odor versions are needed.…”

“…This reliance on self-report leaves estimates of qualitative olfactory disorders likely underrepresented, only diagnosed when individuals consult specialists. However, even with subjective reports, qualitative olfactory disorders are present in more than half of those reporting smell impairment (36)(37)(38), and distinct features of parosmia and phantosmia are beginning to surface (31). Parosmia encompasses distortions of a known odor, often experiencing pleasant odors as unpleasant or vice versa (39), so one way to assess parosmia directly is to have participants rate the pleasantness of two oppositely valenced odors (i.e., a pleasant and unpleasant odor).…”