TASTE AND SMELL DISORDERS
Ronald Devere, MD, Medical Director, Taste and Smell Disorders Clinic, Austin, TX
Educational Objectives
| The goal of this program is to improve the clinical management of taste and smell disorders. After hearing and
assimilating this program, the clinician will be better able to:
|
 | 1. Describe structures in the taste and smell systems.
|
| 2. List common causes of taste and smell loss.
|
| 3. Evaluate patient based on history, symptoms, and clinical findings.
|
| 4. Provide suggestions about food preparation.
|
| 5. Select treatment for dysosmia and dysgeusia.
|
Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the
planning committee to disclose relevant financial relationships within the past 12 months that might create any personal
conflicts of interest. Any identified conflicts were resolved to ensure that this educational activity promotes
quality in health care and not a proprietary business or commercial interest. For this program, Dr. Devere and the
planning committee reported nothing to disclose.
Acknowledgements
Dr. Devere was recorded on May 9, 2008, in the recording studio of the Audio-Digest Foundation, located in Glendale,
CA. The Audio-Digest Foundation thanks Dr. Devere for his cooperation in the production of this program.
| Introduction: disorder affects 8 to 10 million people >55 yr of age in United States; effects on quality of life
(QOL)—weight loss; decreased appetite; depression; less enjoyment of eating; loss of ability to smell outdoors and
fragrances; effects on career (eg, chef, firefighter); safety issues
|
| Olfactory system: olfactory organ in nose comprised of receptors and axons; axons travel through cribriform plate
on front of skull and enter olfactory bulb (where olfactory nerves join); axons enter brain structures (eg, medial
temporal lobe, hypothalamus, amygdala; important for memory and emotion); flavors—food placed in mouth dissolved
by saliva; with swallowing, molecules travel down throat, up airway, and through retropharynx and nose;
smell organ can identify molecules (ie, flavors)
|
| Taste system: structures with taste receptors include taste buds, palate, and pharynx; located throughout mouth; information
taken from front of tongue by fifth nerve branches to seventh nerve through chorda tympani; ninth nerve
(glossopharyngeal nerve) and tenth nerve (vagus nerve) pick up information from back part of tongue and pharynx;
information travels to brain stem, nucleus solitarius, thalamus, and brain; taste information does not go through medial
temporal nerve and hypothalamus (emotional aspect of taste not as strong as that of smell); basic tastants—1)
sweet; 2) sour; 3) bitter; 4) salt; 5) umami (describes taste of monosodium glutamate [MSG; eg, brothy savory
taste]); fifth cranial nerve (ie, trigeminal nerve)—involved in texture, temperature, and spice sensations of food; diseases
of trigeminal nerve result in sensory loss in face and tongue (generally does not impair smell, flavor, or taste)
|
| Presentations: 1) patients complain of smell loss; 2) most patients complain about taste impairment; 90% of people
who complain of taste disorder likely have smell abnormality (10% may have primary taste disorder); complaint of
taste abnormality secondary to smell system dysfunction; 3) some patients do not have any symptoms; patients may
be elderly, cognitively impaired, or have Parkinson's disease or early Alzheimer’s disease; patients complain of
weight loss, decreased appetite, and depression; patients have significant smell and flavor impairment, but do not
complain; many patients considered to have gastrointestinal (GI) problem or underlying cancer
|
| Evaluation of patients with symptoms: thorough history; determine whether smell or taste problem occurred
after head injury, viral infection, upper respiratory tract infection (URTI), or chronic sinus infection, or whether
problem developed gradually; review patient’s medications (eg, calcium channel blockers, diabetic drugs, antidepressants);
consider tobacco smoking; perform physical examination; examine mouth (eg, check dentition and
gums; check for adequate saliva production and coated tongue); University of Pennsylvania Smell Identification Test
(UPSIT)—standardized for sex and age; costs ≈$27; scratch-and-sniff format; comprised of 40 odor-containing
capsules; takes ≈15 min; available in several languages; sensitive; brief smell identification test (B-SIT)—costs ≈$13;
comprised of 12 capsules; sensitive; standardized for age but not sex; whole-mouth taste testing—not standardized;
basic tastants tested with, eg, sugar, citric acid, caffeine, salt (mixed with water in small cup); increase concentration
if patient unable to identify tastant
|
| Results: 1) patients may have anosmia (complete smell loss) with normal taste; identified by UPSIT (eg, patient 60
yr of age who scores 20 points out of 40 has severe anosmia [30 out of 40 indicates mild smell loss]); 2) patients
may have hyposmia (diminished smell) and normal taste; 3) patients may have normal smell with taste impairment
(less common)
|
| Further work-up: computed tomography (CT) of sinuses; magnetic resonance imaging (MRI) of brain in patients
with, eg, history of head injury or headache (order special views of olfactory system); consider vitamin B12 deficiency,
low thyroid function, and low zinc levels (especially in patients with weight loss and GI symptoms); refer to
otolaryngologist for nasal endoscopy to check upper nose for, eg, polyps, cancer, inflammatory disorders
|
| Causes of smell loss: 25% of patients have history of chronic recurrent sinus infections or URTIs, nasal allergies,
or polyps; 25% have smell loss with common cold; 25% have history of trauma to face, head, or brain (7% of patients
with head injury have associated smell disorder); whiplash; normal aging—2% of people <65 yr of age have
smell loss; 50% of people 65 to 80 yr of age, and 75% of people >80 yr of age have impaired smell; smell impairment
may be due to mucosal changes in nose, narrowing of holes in cribriform plate, decreased blood flow in brain
and olfactory organ, or loss of olfactory nerve cells; medications—antibiotics (eg, penicillin); calcium channel
blockers (eg, diltiazem [eg, Cardizem], nifedipine [eg, Procardia]); statins (eg, atorvastatin [Lipitor], pravastatin
[Pravachol]); amphetamines; cimetidine (eg, Tagamet); antidepressants (eg, amitriptyline [Elavil, no longer on market],
paroxetine [eg, Paxil]); phenytoin (Dilantin); diuretics (eg, furosemide [Lasix]); if possible, consider stopping
drug for 3 mo to see whether taste and smell symptoms resolve; toxins—uncommon; pesticides; formaldehyde;
sprays containing creosol; patient history important; tobacco smoking—usually subtracts 4 points from UPSIT
score; other conditions—kidney disease; liver disease; diabetes and diabetic neuropathy; hypothyroidism; alcohol
shown to produce smell impairment in 50% (causes toxicity to temporal lobe and structures involved in memory
and taste and smell pathways; impairment improves with decreased alcohol use)
|
| Neurologic disorders: patients do not complain of taste and smell loss, but present with weight loss, disinterest in
eating, depression, and decreased appetite; consider memory disorders, Alzheimer’s disease, Parkinson’s disease,
and Parkinson’s dementia; 90% of patients have smell problem and secondary flavor abnormality or loss; disorders
cause damage to olfactory system and temporal lobe; patients with multiple sclerosis develop smell impairment
(often asymptomatic); seizure disorder or epilepsy—attacks of bad odor (dysosmia) or bad taste (dysgeusia) usually
last <2 min (attacks lasting >2 min usually not related to brain)
|
| Primary causes of taste loss: less common; aging—threshold for salt or sugar increases; bitter, sour, and umami
usually do not change with age; medications—affect structures of taste system and reduce saliva production; amitriptyline
blocks acetylcholine (acetylcholine necessary for saliva production); diphenhydramine (eg, Benadryl),
furosemide, and tolterodine (Detrol) affect saliva production; captopril and lisinopril affect zinc and function of
saliva; levodopa (L-dopa), phenytoin, and topiramate (Topamax) can affect cranial nerves and taste system; statins;
other conditions—gastroesophageal reflux disease (GERD); vitamin B12 deficiency; thyroid deficiency;
liver and kidney disease; diabetes
|
| Negative effects on QOL: unable to smell good food; unable to smell smoke or other hazards; increased use of
perfume or deodorant may be offensive to others; less enjoyment of eating, due to loss of flavors; risk of eating
spoiled food (eg, unable to detect sour milk); unable to smell outdoors or perfume/fragrance; decreased eating; social
isolation; less cooking; effects on work (eg, firefighters, wine tasters); depression—35% to 50% of sufferers
have depression; many require counseling and antidepressants
|
| Prognosis: 23-yr follow-up study found patients with history of, eg, chronic sinus infection or trauma, continued to
make progress; patients with clear cause of problem (eg, low thyroid function, diabetes) do well with specific treatments;
stopping offending medications usually reverses problem; be aware that some patients with recurrent sinus
infections and allergies do not improve with nasal steroid treatment (may improve with oral steroids for 2 wk in tapering
schedule); patients with Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and progressive disorders
do not improve with treatment; patients with reversible conditions, postviral smell loss, trauma, and chronic
sinus and allergy problems improve; in postviral infections, two-thirds of patients improve over 3 to 5 yr; improvement
in patients with head trauma depends on severity of smell loss (25% of patients with mild smell loss regain
normal smell function over 3-4 yr, 10% with severe smell loss); prognosis based on severity of smell loss rather
than mechanism of smell impairment; prognosis worse if age >75 yr and if time before seeking health care long (eg,
2 yr)
|
| Treatment: based on educating patient about disorder; awareness of health and safety (eg, advise patients to install
smoke detectors, date perishable foods, label household cleaning products); artificial saliva (eg, Xero-Lube); adjustment
of dentures; pilocarpine (acetylcholine enhancer)
|
| Review of taste and smell system: 1) impairment of smell system due to disturbance of smell organ can impair
flavor (eg, chocolate, vanilla) sensitivity; 2) taste system has 5 tastes (ie, sweet, sour, bitter, salt, umami); usually
spared; 3) trigeminal system (sensory system of nose and mouth) important for temperature, texture, and spice
|
| General food tips: choose and prepare foods that smell and look good; use foods with various textures and colors;
chew slowly and move food around mouth to stimulate taste and sensory receptors; alternate bites of various foods
during meal; consider adding spicy condiments; fish, poultry, and meat can be marinaded in sweet fruit juices, Italian
wine sauce, or salad dressing; tart foods (eg, oranges, lemonade) better appreciated in patients with smell disorders;
MSG—undetected by 20% of population with genetic defect; use flavor-enhancer seasoning (eg, Accent) on
steak, chicken, and potatoes; tomatoes and tomato paste contain MSG
|
| Food preparation: pilot study found people without taste and smell problems did not prefer to add spices or condiments
(eg, ginger, MSG) to original recipe of tandoori salmon, while patients with taste and smell disorders preferred
various combinations of additional spices; give patients alternative choices to compensate for taste disorder
by adding more spices and changing texture (affects QOL)
|
| Counseling: patients may require antidepressants or referral to psychologist
|
| Dysosmia: unpleasant putrid smell from, eg, viral infection or head injury; “smells like rotten eggs”; affects QOL; 1)
parosmia; bad smell triggered by, eg, certain food; 2) phantosmia; spontaneous bad smell; dysosmia almost “always
gets better”; can last from 6 mo to 3 yr; treatment—squirt 5 to 10 mL of normal saline in each nostril while in head-
down position (blocks airway to prevent triggering of bad smell); anticonvulsants, eg, gabapentin (eg, Neurontin;
use ≤300 mg tid and slowly increase dose; no good published data available) or zonisamide (Zonegran, 100 mg
bid); removal of smell organ (aggressive therapy; successful; last resort)
|
| Dysgeusia: horrible taste triggered by certain foods; taste may be metallic or bitter; predominantly occurs in patients
with primary taste disorder; caused by medications (eg, topiramate) and can interfere with taste of carbonated beverages;
phantogeusia (occurs spontaneously); treatment—lozenges containing benzocaine and menthol (eg, Cepacol
lozenges); mouthwash containing lidocaine; gabapentin; zonisamide
|
| Summary: management includes patient history, investigating causes, and smell testing; nasal endoscopy by otolaryngologist
important; consider referral to neurologist; consider patient’s QOL; changes in food preparation easily
done; narcotics—sniffing crack cocaine can cause damage to smell organ; amphetamines taken intravenously
(IV) or orally can affect taste and smell; heroin and codeine affect taste and smell; toxins—formaldehyde; carbon
disulfide; related to petroleum industry; people exposed to bad odors in environment that may not necessarily cause
toxic effect do not have changes in smell system “unless it’s a real toxin that causes damage”
|
Suggested Reading
Aschenbrenner K et al: The influence of olfactory loss on dietary behaviors. Laryngoscope 118:135, 2008; Devere
R: Taste and smell disorders: a view from clinical practice. ChemoSense 6:1, 2003; Doty RL et al: Drug-induced
taste disorders. Drug Saf 31:199, 2008; Doty RL: Clinical studies of olfaction. Chem Senses 30 Suppl 1:i207,
2005; Doty RL: Office procedures for quantitative assessment of olfactory function. Am J Rhinol 21:460, 2007;
Gardiner J et al: Defects in tongue papillae and taste sensation indicate a problem with neurotrophic support in
various neurological diseases. Neuroscientist 14:240, 2008; Gudziol V et al: Clinical significance of results from olfactory
testing. Laryngoscope 116:1858, 2006; Hummel T et al: Effects of olfactory function, age, and gender on
trigeminally mediated sensations: a study based on the lateralization of chemosensory stimuli. Toxicol Lett 140, 2003;
Igarashi A et al: The salivary protein profiles in the patients with taste disorders: the comparison of salivary protein
profiles by two-dimensional gel electrophoresis between the patients with taste disorders and healthy subjects. Clin
Chim Acta 388:204, 2008; London B et al: Predictors of prognosis in patients with olfactory disturbance. Ann Neurol
63:159, 2008; Mallick HN: Understanding safety of glutamate in food and brain. Indian J Physiol Pharmacol
51:216, 2007; Tourbier IA et al: Sniff magnitude test: relationship to odor identification, detection, and memory
tests in a clinic population. Chem Senses 32:515, 2007.
|
