Olfactory Impairment and Disease Etiology are Linked

Does the pattern of olfactory impairment seen in psychophysical testing reflect underlying disease etiology?

Bottom line
Patterns of olfactory impairment do reflect underlying disease etiology, but multicomponent olfactory testing should be used, especially if there is diagnostic uncertainty.

Background: Olfactory function is assessed clinically using psychophysical testing, where different aspects can be defined to include odor threshold, discrimination, and identification. Certain conditions lead to selective olfactory subcomponent impairment, so different disease etiologies should theoretically lead to differing patterns of olfactory impairment. However, previous work suggests that different olfactory tests actually measure a common source of variance.

Study design: Retrospective cohort analysis of 1,226 patients from 2000 to 2012 who had olfactory dysfunction due to post-infectious olfactory loss (PIOL), post-traumatic olfactory loss (PTOL), olfactory loss secondary to sinonasal disease (OLSSD), and olfactory loss secondary to Parkinson disease (OLAPD).

Setting: Smell and Taste Clinic, Department of Otorhinolaryngology, Technische Universität Dresden, Germany.

Synopsis: Patients with PIOL had significantly higher scores compared to those with PTOL or OLAPD, and patients with OLSSD scored significantly lower than patients with OLSSD. Significant interaction between the factors “test” and “etiology” indicated that different hyposmia causes produce different olfactory loss patterns, although the effect size was relatively low. PIOL patients scored comparatively well in discrimination and threshold but poorly in identification; PTOL patients showed similar patterns but with reduced scores. Patients with OLSSD had the lowest scores in threshold but performed comparatively well in discrimination and identification. OLAPD patients performed comparatively well in threshold but poorly in both discrimination and identification.

Olfactory loss onset was more sudden in PIOL and PTOL patients than in patients with OLSSD, while patients with OLAPD described both sudden and gradual onsets. Olfactory function fluctuation was seen least frequently in patients with PIOL and PTOL but more often in cases of OLSSD. Olfactory function improvement over time was seen most frequently in patients with PIOL and least frequently in patients with OLAPD.

Citation: Whitcroft KL, Cuevas M, Haehner A, Hummel T. Patterns of olfactory impairment reflect underlying disease etiology. Laryngoscope. 2017;127:291–295.