Smell in Sjögren’s Syndrome
New studies fail to push the envelope
Sjögren’s Syndrome is an immune system disorder commonly characterized by dry mouth or dry eyes. Since the mucus membranes of the olfactory epithelium are critical to odor perception the link between smell and Sjögren’s syndrome has been a topic of interest.
This year has seen a bumper crop of smell studies on Sjögren’s. A research team in Turkey (Topan, et al., 2021) found what they characterize as mild clinical impairment in smell among Sjögren’s patients, which appears to be moderately correlated with dry eye symptoms as well.
Researchers in the UK (Kamel & Maddison, 2021) reported that 47% of Sjögren’s patients scored in the hyposmic range on a measure of odor detection threshold; this was significantly greater than the percentage found in a control group.
Finally, a group of researchers in China (Xu, et al., 2021) report that anosmia and hyposmia were significantly higher in Sjögren’s patients than controls, and that olfactory dysfunction was positively correlated with disease severity.
What are we to make of all these studies? First, note that the core pathology of Sjögren’s syndrome—dry mucus membranes—affects the olfactory system at its periphery by interfering with the initial transduction of a chemical signal into an electrical one in the sensory neurons. (Incoming odorant molecules dissolve into the mucus layer where the olfactory receptors reside on the cilia of the sensory neurons.) It doesn’t tell us much about how odor perception is organized physiologically or cognitively.
Secondly, these studies break no new ground. Richard Henkin and colleagues first reported the Sjögren’s-smell connection back in 1972. The late James Weiffenbach and his colleague confirmed the link in 1993. At best, the studies of 2021 are incremental advances to the field. At worst, they may be a glorified form of clinical busy work that serves career advancement more than science.
Topan, Y.E., Bozkurt, B., Yılmaz, S., Elsürer, Ç., Gorcuyeva, S., & Bozkurt, M.K. (2021). Olfactory dysfunction in primary Sjogren’s syndrome and its correlation with dry eye. Acta Otorhinolaryngologica Italica, 41(5), 443–449.
Kamel, U.F., & Maddison, P.J. (2021). Rhinological manifestations of Sjögren's syndrome: a cohort-matched, prospective, cross-sectional, observational study. The Journal of Laryngology and Otology, 135(10), 932–936.
Xu, X., Geng, L., Chen, C., Kong, W., Wen, B., Kong, W., Chen, S., Zhang, H., Liang, J., & Sun, L. (2021). Olfactory impairment in patients with primary Sjogren’s syndrome and its correlation with organ involvement and immunological abnormalities. Arthritis Research & Therapy, 23(1), 250.