AsianScientist (Nov. 16, 2016) – Researchers from the University of Tokyo have developed a test that can distinguish between the two possible causes of the loss of the sense of smell. Their results have been published in Scientific Reports.
Many of us have experienced a loss of smell when suffering from nasal inflammation or infection. A runny or stuffy nose can block nasal passages and cause what are known as conductive disorders that prevent odors from reaching the olfactory nerve; another way that we can lose our sense of smell is through neural disorders caused by damage to the olfactory nerve itself.
Treatment for olfactory conditions varies significantly depending on which of the two types of disorders—conductive or neural—is causing the symptoms; therefore, determining the root cause is important in devising an effective course of treatment, but a smell test for selectively detecting neural disorders and distinguishing them from conductive disorders was not available.
The intravenous olfactory (IVO) test is widely used as a way to evaluate a person’s sense of smell. The test checks the subject’s ability to recognize odors by injecting thiamine (vitamin B1) into the vein; the vitamin’s odor proliferates in the relatively enclosed cavity of the lung’s air sacs and increasing numbers of olfactory sensory neurons are stimulated over a short period of time through respiratory activity.
Studying patients suffering from chronic rhinosinusitis, a condition that arises from a combination of both conductive and neural causes, researchers led by Professor Tatsuya Yamasoba found that the time lag (latency period) between the injection of thiamine and the onset of sensory neuron stimulation could be used to differentiate between conductive and neural disorders.
Patients who had a slower onset of sensory neuron stimulation showed almost no improvement in their symptoms following endoscopic surgery to improve airflow, thereby implying that neural disorders rather than conduction issues were the source of their symptoms.
In mice injected with thiamine intravenously, the latency period did not change for the animals afflicted with conductive disorders, but was prolonged for those with neural disorders. Furthermore, the researchers observed a correlation between longer latency and the severity of disorders in olfactory epithelium, the nasal tissue involved in smell.
“We are pleased to come up with a novel application for the IVO test,” said Yamasoba. “We are hopeful that it will prove useful in the cause-based classification of patients with olfactory disorders, and contribute toward selecting appropriate therapies, as well as in making prognoses.”
The article can be found at: Kikuta et al. (2016) Longer Latency of Sensory Response to Intravenous Odor Injection Predicts Olfactory Neural Disorder.
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Source: University of Tokyo; Photo: Pixabay.
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