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Logo of bmjThis ArticleThe BMJ
 
BMJ. 2007 September 22; 335(7620): 588–589.
PMCID: PMC1989003
Sensory Research

Scent trails

Geoff Watts, freelance journalist

Smells form some of our most memorable experiences, but people who cannot detect them are largely forgotten. Geoff Watts sniffs out the researchers

Tell the world that you are blind or deaf or have no sense of touch and you can count on a measure of sympathy. But say that you have lost your sense of smell and the response will be, likely as not, indifference. We humans are not animals, are we? Of all our senses, smell is the least important.

Maybe so—but that is small consolation to people with the problem. Still more dispiriting for them is the lack of medical interest in disorders of smell, whether in treatment or research. Of the handful of UK clinicians with a special interest in the topic, two of the most active took it up more or less by chance and have to combine it with other work.

Unmet need

Evidence on the prevalence of olfactory disorders is patchy and conflicting. Tim Jacob, a physiologist who teaches a course on the senses at Cardiff University and also does research on smell, talks of American figures suggesting that around 2% of the population have a problem. But he can't be sure. He's on firmer ground when talking qualitatively.

“About 12 years ago,” he says, “I set up a website on smell. I was flooded with emails and phone calls from people who'd lost their sense of smell or taste. People who were desperate. People who felt that the health system had let them down. Their GPs had said there was nothing that could be done, and they should go away and just learn to cope.”

Affected people, it seems, aren't getting answers to even the most basic questions such as the likely outcome of the condition, whether the loss can be remedied, and whether it may be a harbinger of worse to come. The effect of this on some people's lives is severe. It causes distress and, in some cases, depression.

Glenis Scadding, a consultant allergist and rhinologist at the Royal National Throat, Nose, and Ear Hospital, became interested in smell through dealing with nasal polyps. Whether patients seeking help actually receive any depends on the individual general practitioner, she says. As word gets back to referring doctors that she can treat smell problems related to polyps, they sometimes begin (though whether through optimism or desperation isn't clear) sending her more patients. “I've ended up seeing a load of people who don't have polyps but have smell problems with other causes.” By and large, she adds, most general practitioners refer patients to ear, nose, and throat departments. But the chances of getting much truly informed help are slim simply because so few clinicians take a serious interest in the condition. In the abbreviation ENT it's the E and T that are writ large; it might more aptly be rendered EnT.

Chris Hawkes is a consultant neurologist at Queen's Hospital, Romford. His interest in smell disorders was prompted in part by wondering if motor neurone disease might be the outcome of a toxin entering the body through the nose.1 This led him to study the impairment of smell not only in motor neurone disease but in other neurological conditions such as multiple sclerosis, Alzheimer's disease, and essential tremor as well as Parkinson's disease, in which smell is often seriously impaired and probably one of its first symptoms.

He gets a trickle of patients from all over the place—sometimes because they have seen his name on the web and pressed their general practitioner for a referral. Does he too think that his fellow clinicians are dismissive of smell? “All the time,” he says. “Or at least 95% of it.” And interest in taste problems, he thinks, is even lower.

Unrealistic patient demand for a cure where none exists is not, as you might imagine, a big problem according to one of the leading American authorities on olfaction. Richard Doty, professor of otorhinolaryngology at the University of Pennsylvania and director of its smell and taste clinic, sees one of his tasks as helping patients put their problems in perspective. “Many of the patients referred to us have been batted around the system and are sort of looking for closure; for people who actually know what they're talking about. Many who we may not be able to help surgically or medically are still happy to have come here.” Even those who are told that nothing can be done at least have the satisfaction of a definitive opinion. They are free to stop seeking a remedy and concentrate instead on learning to live with the condition.

“It's also therapeutic to have all these people out in the waiting room talking to each other on our clinic days,” says Professor Doty. “They realise they're not alone.”

Science of smell

On both sides of the Atlantic the general approach to disorders of smell is broadly similar: look for an underlying cause to which the loss is secondary and tackle that. Nasal polyps, says Dr Scadding, are usually though not always pretty obvious. “We've learnt from people with polyp regrowth that the sense of smell can go before you can see any sign of the polyps. So it may not be physical blockage; it may be inflammation. But we're not certain.”

Injury to nerves where they come through the skull is another cause. Even a small knock to the head can sever these nerves. Viral infections may trigger a loss of smell, as may neurodegenerative disease. And there are also various less common causes ranging from brain tumours to the side effects of drugs.

Researchers are continuing to try to find ways to treat loss of smell. To this end Dr Hawkes, Dr Scadding, and Professor Jacob would love to see even one properly funded taste and smell clinic in the United Kingdom, ideally backed up by research facilities. But they are not holding their breath.

Like many clinicians and researchers with ideas to explore and therapies to test, they cast wistful glances across the Atlantic. Indeed, spend half an hour on the web and you might conclude that the United States has at least a dozen clinics with a serious interest in taste and smell, many of them university based. But speaking from the US, Professor Doty is more cautious. For a start he doesn't think that medical views there are so different from those in Britain. “There's an attitude that if I can't do anything about it, why bother.”

But what about all these clinics? He laughs. “There's a tendency on the part of people in foreign countries to think that things must always be better in the United States. But that isn't always the case. As for the clinics, there are places that will do some testing, but not many that will carry out a thorough assessment. And those that do do thorough assessments sometimes limit their patients to certain groups because they're doing research.” In short, while more is certainly available there, the provision is not quite as it first seems. And as ever in a system that strives to give consumers what they want, an entrepreneurial enthusiasm for meeting their needs may outstrip the scientific justification for what's being offered.

From the vantage point of his clinic, Professor Doty is well placed to take a view of the future. Although he can foresee possibilities, he's cautious about the likely rate of progress. The formation of scar tissue in nerves after head trauma, for example. “The cells still want to regenerate and they're sending axons all over the place, but they're not making the right connections.” Developments in stem cell biology offer the most hope—but not in the short term. Although he is also encouraged by recent developments in gene therapy for retinal disease,2 their applicability to olfactory receptors is still an open question.

In the meantime, people who have lost their sense of smell must continue resigning themselves to widespread indifference. This irritates Professor Jacob. “How people underestimate the importance of smell in their lives,” he says. “Yet everything you do in life is done against the backdrop of your olfactory system. It has an impact and influence that most of us are completely unaware of.” Perhaps Dr Scadding puts it best. She describes being deprived of your sense of smell as the olfactory equivalent of living in a world where the only colours are black and white.

Notes

Competing interests: None declared.

References

1. Hawkes CH, Shephard BC, Geddes JF, Body GD, Martin JE. Olfactory disorder in motor neuron disease. Exp Neurol 1998;150:248-53. [PubMed]
2. UCL Institute of Ophthalmology. First trial of gene therapy for childhood blindness. www.ucl.ac.uk/ioo/research/researchers/clinical_trials.html

Articles from The BMJ are provided here courtesy of BMJ Publishing Group