Importance: Olfaction is a complex sensory process that has not been fully studied. Elevated plasma levels of interleukin 6 (IL-6) have been found in patients with several acute and chronic diseases but have not been reported in patients with smell loss (hyposmia).
Objective: To determine IL-6 levels in patients with hyposmia.
Design: Retrospective study. All measurements were made without reference to the origin of any collected sample. SETTING An ambulatory private practice at The Taste and Smell Clinic in Washington, DC.
Participants: Fifty-nine consecutive patients who presented to the clinic between 2005 and 2008 for evaluation and treatment of various degrees of hyposmia were studied. Nine volunteers with normal sensory function served as controls.
Main outcomes and measures: Levels of IL-6 were measured in samples of plasma, urine, saliva, and nasal mucus.
Results: All biological fluid samples studied contained IL-6. Mean (SEM) levels in plasma, saliva, and nasal mucus in patients were significantly higher than in controls (0.95 [0.10] vs 0.12 [0.03] pg/mL, 0.57 [0.05] vs 0.30 [0.01] pg/mL, and 29.7 [3.8] vs 11.6 [0.5] pg/mL, respectively; all P < .001). The concentration of IL-6 in nasal mucus in patients was significantly higher than in controls and was more than 30 times higher than in any other biological fluid. Mean (SEM) levels in urine were not significantly different: 0.92 (0.17) pg/mL for patients and 1.26 (0.41) pg/mL for controls (P > .50).
Conclusions and relevance: Compared with controls, IL-6 in patients was significantly elevated in plasma, saliva, and nasal mucus. Because IL-6 is a proinflammatory cytokine, these changes can relate to local or systemic inflammatory processes, which can be a cause or a result of pathological processes associated with hyposmia. These results support the concept that hyposmia has a biochemical basis and IL-6 may play a role in biochemical pathological processes underlying hyposmia and its treatment.