Smell Disorders

Nerves in the septum (middle divider) of the nose. Right side. Source: Gray's Anatomy.

Smell disorders, or olfactory disorders, include either a loss in a person's ability to smell, or changes in the way they perceive odors. Sensory cells in the nose, mouth, and throat help to interpret smells. Microscopic molecules released by substances in the environment (such as trash, food, or flowers) stimulate these cells. Once the cells detect the molecules, they send messages to the brain, which identifies the smell.

Because the perception of flavor comes from a combination of odors and taste, it is also affected by smell disorders.

There are numerous kinds of smell disorders. Though many are benign, some can indicate a more serious underlying neurological condition.

Types

There are three main types of smell disorders:

• Anosmia (loss of smell)
• Hyposmia (reduced ability to smell)
• Hypersomia (oversensitivity to smell)

Signs and Symptoms

Symptoms vary depending on the cause and extent of disturbance in smell. The ability to smell may be decreased, absent or alterered.

Causes

Smell disorders have many causes. The problem may originate from the nose itself, the nerves leading to the brain, or the brain. The three most common causes of smell disorders are: (1) a head injury, (2) an upper respiratory infection or sinus infection, and (3) growths (polyps) in the nasal cavity.

Other causes of smell disorders include hormonal disturbances (such as pregnancy), dental problems, exposure to certain chemicals (such as insecticides and solvents), and the use of certain medicines (the list is long, but the most common are ACE inhibitors). People with head and neck cancers who receive radiation treatment also often experience problems with their sense of smell.

As with vision and hearing, people gradually lose their ability to smell as they get older. Smell that declines with age is called presbyosmia and is not preventable. Before a doctor diagnoses presbyosmia, though, he or she should make sure that something more serious is not causing the loss of smell in an older person. Presbyosmia is a diagnosis of exclusion. ^[1]

Diagnosis

Medical history

Information a doctor will need from a patient when trying to diagnose the cause of a smell disorder include the following.

• Any history of head trauma, sinus infection, or allergies
• Medications taken
• When the impairment began
• Whether the problem is worsening
• Whether all or only some odors are affected
• Whether the sense of taste is altered
• Tobacco or cocaine use, since these substances can adversely affect the sense of smell
• Diet
• Any history of dryness of the mouth, periodontal disease, foul breath odor, recent dental procedures, recent radiation exposure, or gastric reflux.
• Family history of a disease such as diabetes mellitus or hypothyroidism

Physical examination

The doctor should examine the head and neck to look for obstruction, inflammation and infection. The mucus membranes should be examined carefully for disease. He or she should also check the teeth, as dental disease can disturb the senses of smell and taste.

A careful examination of the cranial nerves, or nerves to the face and head, should be done. This exam consists of asking the patient to perform a series of simple maneuvers like shutting the eyes tight and puffing out the cheeks. Damage to the seventh cranial nerve may lead to alterations in taste involving the front two-thirds of the tongue, decreased salivation, oversensitivity to sound, or facial paralysis.

Tests

Tests for smell disorders are designed to measure the smallest amount of odor patients can detect, as well as how accurately they can identify different smells.

An easily administered Smell Identification Test (scratch and sniff test) allows a person to scratch pieces of paper treated to release different odors, sniff them, and try to identify each odor from a list of possibilities. In this way, doctors can easily determine whether a person has hyposmia, anosmia, or another kind of smell disorder. Other commercially available tests for smell include the Pocket Smell Test, the Brief Smell Identification Test and a squeeze-bottle odor threshold test kit.

Radiologic tests

Radiologic tests, including X-rays, CT scans, or MRI scans, may be helpful in diagnosing the cause of a smell disorder, especially if infection or growths are suspected.

X-rays can provide a view of the sinuses, which may help to diagnose sinus disease. They cannot detect most other causes, however.

A Computed tomography (CT) scan is considered the most useful and cost-effective technique when available. Coronal CT scans (those whose images "slice" in an ear-to-ear direction) are particularly good at showing the anatomy of the nasal passages and sinuses. CT scanning is less effective than magnetic resonance imaging (MRI) in defining soft tissue disease (as opposed to bone), though. The use of intravenous contrast dye helps to better identify abnormalblood vessels, tumors, pockets of pus (abscesses) and problems with the brain or the lining of the brain.

Magnetic resonance imaging (MRI) is better than CT scanning when a physician wants to look at soft tissues like the brain or the lining of the nose, but it does not define bone as well as CT does. MRI is the technique of choice for assessing the parts of the olfactory (smell) system called the olfactory bulbs and olfactory tracts, as well as the facial nerve and the brain itself.

Treatment

Some people recover from smell disorders. Since certain medications can cause a problem, adjusting or changing that medicine may ease its effect on the sense of smell. Others recover their ability to smell when the illness causing the problem resolves. For patients with nasal obstructions such as polyps, surgery can remove the obstructions and restore airflow. Not infrequently, people enjoy a spontaneous recovery because nerve cells that control smell may regrow following damage.

Medications

If a person's smell loss is caused by hay fever or allergic rhinitis, steroids sprayed inside the nose may help. ^[2]

Holistic and alternative treatments

Zinc has been proposed as an alternative treatment for smell disorders, especially those caused by head injury or an upper respiratory infection like a coldor sinusitis. Other treatments include garlic supplements, vitamin C, and avoiding dairy products. These treatments have not been studied extensively, so it is not known how safe they are or whether they work. As witih all unstudied treatments, they should be used with caution, and only after any serious or surgically reversible causes of smell disorder have been ruled out.

Living with a Smell Disorder

Like all the senses, smell plays an important role in survival and in quality of life. The sense of smell often serves as a first warning signal, alerting a person to, for example, a fire or gas leak. People with a smell disorder should check their smoke alarms, but fire extinguishers, and may want to invest in a natural gas detector, which uses an alarm and/or a light to warn of a natural gas leak. If they have gas stoves they may want to change to electric.

They should also pay careful attention to when food was bought and stored, as they may not be able to tell by odor whether food is spoiled.

People who have trouble smelling may also lose some pleasure in tasting food, which may lead to appetite loss, or to overeating to compensate for a lack of taste.

Related Problems

Disorders of smell and taste (called the chemosenses, since they rely on the body's contact with chemicals) are sometimes a signal of more serious health problems. Obesity, diabetes, hypertension, malnutrition, Parkinson disease, Alzheimer disease, multiple sclerosis, and Korsakoff psychosis may all be accompanied or signaled by a smell disorder.

Clinical Trials

American government-sponsored clinical trials relating to smell disorders include the following.

• Is Pentoxifylline Able to Improve Olfactory Sensitivity?
• Orexigenic Therapy With Delta-9-Tetrahydrocannabinol in Advanced Cancer Patients With Chemosensory Abnormalities - a Pilot Study

For a complete list, click here.

Research

In the United States, the National Institute of Deafness and Other Communication Disorders (NIDCD) supports basic and clinical investigations of chemosensory disorders at many different institutions. Some of these studies are making advances that help with a better understanding of the olfactory system and may lead to new treatments for smell disorders.

NIDCD's research program goals for chemosensory sciences include

• Promoting the regeneration of sensory and nerve cells
• Appreciating the effects of the environment (such as gasoline fumes, chemicals, and extremes of relative humidity and temperature) on smell and taste.
• Preventing the effects of aging.
• Preventing infectious agents and toxins from reaching the brain through the olfactory nerve.
• Developing new diagnostic tests.
• Understanding associations between chemosensory disorders and altered food intake in aging as well as in various chronic illnesses.
• Improving treatment methods and rehabilitation strategies.

Expected Outcome

The best thing a person who suspects they have a smell disorder can do is see a doctor. Proper diagnosis by a trained professional, such as an otolaryngologist, is important. These physicians specialize in disorders of the head and neck,especially those related to the ear, nose, and throat. Diagnosis may lead to an effective treatment of the underlying cause of the smell disorder. Many types of smell disorders are curable, and for those that are not, counseling is available to help people cope.

Epidemiology

Prevalence

Approximately 2 million people in the United States have a smell disorder. ^[3]

Notable experts

A list of smell (and taste) referral centers (from the American Academy of Family Physicians):^[4]

Chemosensory Clinical Research Center 925 Chestnut St. Philadelphia, PA 19107 Telephone: 215-955-5652

Clinical Olfactory Research Center State University of New York Health Science Center at Syracuse College of Medicine 750 E. Adams St. Syracuse, NY 13210 Telephone: 315-464-5588

Connecticut Chemosensory Clinical Research Center University of Connecticut Health Center 263 Farmington Ave. Farmington, CT 06032 Telephone: 860-679-2459

MCV Smell and Taste Clinic Medical College of Virginia, Virginia Commonwealth University P.O. Box 980551 Richmond, VA 23298-0551 Telephone: 804-828-9350

Nasal Dysfunction Clinic University of California, San Diego, Medical Center 9350 Campus Point Dr. La Jolla, CA 92037 Telephone: 858-657-8590

Office of Health Communications National Institutes of Health NIH Building 31, Room 3C-35 31 Center Dr., MSC 2320 Bethesda, MD 20892 Telephone: 301-496-7243

Rocky Mountain Taste and Smell Center University of Colorado Health Science Center Denver, CO 80262 Telephone: 303-315-6600

University of Cincinnati Taste and Smell Center University of Cincinnati College of Medicine 222 Piedmont Ave. Cincinnati, OH 45219 Telephone: 513-558-5469

University of Pennsylvania Smell and Taste Center Hospital of the University of Pennsylvania 3400 Spruce St. Philadelphia, PA 19104-4283 Telephone: 215-662-6580

References

1. ↑ Rawson NE. Olfactory loss in aging. Sci Aging Knowledge Environ. 2006 Feb 8;2006(5):pe6. Abstract
2. ↑ Golding-Wood DG, Holstrom M, Darby Y, Scadding DK, Lund VJ. The treatment of hyposmia with intranasal steroids. J Laryngol Otol. 1996 Feb;110(2):132-5. Abstract
3. ↑ Spielman AI. Chemosensory function and dysfunction. Crit Rev Oral Biol Med.1998;9(3):267-91. Abstract
4. ↑ Bromley S. Smell and Taste Disorders: A Primary Care Approach. Am Fam Physician.2000 Jan 15;61(2):427-36, 438. Abstract | Full Text

External Links

Ansomia foundation