Anosmia: Smelling Function In A Bottle

13. June 2017
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Smelling disorders are not at all a rarity. They can reduce life quality and have a negative impact on eating habits. Rhinologists have now developed a nasal spray which is able at least in part to restore smelling function.

Not being able to smell seems at first thought a harmless matter. However a diminished or fully absent sense of smell can lead to significant limitations: those affected enjoy drinking and eating less, since a large part of flavour is derived from aromatic substances. Smelling disorders can lead to too much or too little being eaten, or too much salt or sugar being added – and to the not insignificant consequence related to this. Not being able to perceive smell can also impact upon social relationships and mental well being. Pleasant odours contribute to positive feelings; many people who have no sense of smell then miss out on the familiar smells of partners and children. Last but not least: the sense of smell is an important warning system in the body – it alerts us to fire, gas or rotten smells and can thus protect us from life-threatening dangers.

British and German scientists have now tested a substance which can be applied as a nasal spray and can at least temporarily restore the ability to smell in patients with full or partial loss of smelling function. Scientists led by Carl Philpott of the University of East Anglia (UEA) in Norfolk (Great Britain) and Thomas Hummel from the Interdisciplinary Center For Smelling and Tasting at the TU Dresden (Germany) employed sodium citrate in their study, a substance already approved for other medical purposes, for example in the stomach and bladder regions, and is considered a safe medicine.

Temporary improvement of olfactory function

Sodium citrate is able to bind calcium molecules, which are presumably involved in a reduction of the sense of smell. The scientists then wanted to find out whether a reduction of calcium in the nasal mucus causes the capacity to smell to be less strongly affected. “Sodium citrate spray was developed to ‘clean out’ calcium molecules in the nasal mucus and restore the sense of smell for a period of time”, Philpott explains. An earlier study had already given indications that sodium citrate can have such an effect – but this was only tested on a small patient group.

In the recent randomised and double blind study, 55 patients with non-sinunasal olfactory disorders participated whose sense of smell was impaired by damage to the olfactory apparatus – for example by a traumatic brain injury, viral infections or toxic and harmful substances. In the case of sinunasal olfactory disorders, on the other hand, there is a hindrance to air flow on the way to the nasal mucous membrane – for example, via inflammation of the nose or of the nose sinuses, due to adenoids or allergy. Half of the subjects received the sodium citrate spray, the other half sterile water. The patients then took part in an odour test, in which they were to inhale four different odours – rose, pear, vinegar and menthol – in increasing concentrations.

Side effects minor

“The results show an improvement in olfactory capacity among those treated with the sodium citrate spray”, Philpott reports. “The effect lasted up to two hours”. The improvement was most pronounced 30 to 60 minutes after the application. However, only one-third of the patients responded to sodium citrate. “The spray seems to be most effective in patients whose olfactory function has been damaged by viral infection”, Philpott explains. The side effects of the treatment were slight: the patients reported mild symptoms such as a running nose, throat or itching.

Another similar study by Thomas Hummel and his team at the TU Dresden also showed that in comparison to a placebo spray sodium citrate leads to improved odour detection in patients whose olfactory capacity has been impaired by an infection.

Studies of long-term use required

The studies suggested that sodium citrate used as a nasal spray could improve a damaged sense of smell, according to the authors. Accordingly, the substance has a certain potential for the treatment of non-sinunasal olfactory disorders, the authors say. “Nevertheless, the results should be reviewed through further major clinical trials which investigate the effects of long-term, regular use of the spray”, Philpott emphasises. The researchers are already planning to investigate this in further studies in which the subjects use the sodium citrate spray several times a day over a longer time.

At the same time, it should also be noted that different regions of the olfactory apparatus can be affected by different types of olfactory disorders, according to the authors. “It is therefore necessary to examine the particular types of olfactory disorders which the sodium citrate spray particularly effectively counteracts”. Only after such investigations would the decision be able to be made as to whether the spray should be routinely prescribed by doctors.

Assuming this happens, an easy-to-use, safe treatment method could at least temporarily restore the sense of smell and thus improve the quality of life of patients. “Sodium citrate could on the one hand be used for the short-term improvement in olfactory function, so that the affected meal times might again be enjoyed and food intake improved”, the authors write. “However, it could on the other hand also be applied on a regular basis and thus improve the olfactory capacity in the long run”.

Non-smelling is not uncommon

Overall, disorders of olfactory function are not uncommon: millions of people worldwide suffer from anosmia. The older a person is, the higher the probability of a limited sense of smell: among those people over 52 years of age, every fourth has a diminished sense of smell, among over-70 year-olds every third already has a pronounced olfactory problem.

So far, there have only been limited options for treating olfactory disorders. “Where sinunasal olfactory disorders are present, in addition to nasal rinses, anti-inflammatory and decongestant agents are able to be used – which contain for instance cortisone. They can be used in tablet form for a short time period, and then as a nasal spray”, explains Hummel. “Antibiotics can also be indicated here. Should this therapy not be successful, an operation can also be considered”.

Where non-sinunasal olfactory disorders are present, olfactory training – whereby the affected individuals are supposed to regularly sniff four different fragrances over several months – has proven effective. “A meta-analysis by our working group has shown that patients experience a significant improvement. A complete cure of olfactory disturbance is, however, rarely possible”, reports Hummel.

More consideration for doctors and ENT hospitals

Traditionally, smelling is regarded as a less important sense, because impairments of vision or hearing lead to markedly more severe limitations, according to the researcher. “In recent years, however, olfactory disorders are being increasingly taken up by doctors and ENT hospitals and are being increasingly taken into account in diagnostics and treatment”, Hummel says. In the meantime, an international standardisation has come to exist, which can be used by ENT specialists and clinics for diagnostics.

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Calcium molecules?

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