Smell & Taste Disorders Disease

DESCRIPTION

The senses of smell and taste allow full appreciation of the flavor and palatability of foods and also serve as an early warning system against toxins, polluted air, smoke and spoiled food products. Physiologically, the chemical senses aid in normal digestion by triggering gastrointestinal secretions. Smell or taste dysfunction can have a significant impact on quality of life. Loss of smell occurs more frequently than loss of taste, and patients frequently confuse the concepts of "flavor loss" (as a result of smell impairment) with "taste loss" (impaired ability to sense sweet, sour, salty or bitter).
Smell - anatomy and physiology:
- The human sense of smell depends on the functioning of not only cranial nerve I (olfactory nerve) but also portions of cranial nerve V (trigeminal nerve). Qualitative odor sensations (e.g., the smell of a rose, lemon or grass) are mediated by cranial nerve I, whereas somatosensory overtones of odorants (e.g., warmth, coolness, sharpness and irritation) are mediated by the ophthalmic and maxillary divisions of cranial nerve V. Smell receptors are located within the olfactory neuroepithelium, a region of tissue found over the cribriform plate, the superior septum and a segment of the superior turbinate. The free nerve endings of cranial nerve V are located diffusely throughout the nasal respiratory epithelium, including regions of the olfactory neuroepithelium. It is important to remember the distinctive nature of these two neural systems, because some odorants (e.g., ammonia) are sensed largely by the trigeminal nerve. Once odorants enter the nose, they must move to the nasal vault and dissolve within the covering mucous layer in order to stimulate the olfactory receptors. Mucous has an important role in dispersing scents to the underlying receptors. The nasal turbinates are also important because they provide moderate resistance and a moist environment, thereby allowing optimal stimulation of olfactory neurons by airborne compounds.
Taste - anatomy and physiology:
- Many nerves are responsible for transmitting taste information to the brain, including cranial nerves 7, 9, 10. Because of these multiple pathways, total loss of taste (ageusia) is rare. As in the olfactory system, somatosensory sensations (e.g., stinging, burning, cooling and sharpness) can be induced by many foods (e.g., hot peppers) through trigeminal nerve fibers in the tongue and oral cavity. Taste receptors are found within taste buds located not only on the tongue but also on the soft palate, pharynx, larynx, epiglottis, uvula and first one third of the esophagus. Taste buds are continually bathed in secretions from the salivary glands, and excessive dryness can distort taste perception.
System(s) affected: Nervous
Genetics: Smell and taste disturbances may be related to genetically-associated underlying diseases (eg, Kallmann's syndrome, Alzheimer's disease, migraine, and rheumatologic and endocrine disorders)
Incidence/Prevalence in USA: Estimated > 2 million; 200,000 visit a physician each year
Predominant age:
- Chemosensory loss is age-dependent
  - Age > 80 - 80% have major olfactory impairment; nearly 50% are anosmic
  - Ages 65-80 - 60% have major olfactory impairment; nearly 25% are anosmic
  - Age < 65 - 1-2% have smell impairment
Predominant sex: Male > Female (men also begin to lose ability to smell earlier in life than women)

SIGNS AND SYMPTOMS

Problems with smell and taste
Weight loss
Malnutrition
Impaired immunity
Worsening of medical illness
Increased use of sugar and salt to compensate for diminished senses of smell and taste

CAUSES

Possible causes of smell disturbance:
- Nasal and sinus disease
- Upper respiratory infection
- Head trauma
- Cigarette smoking
- Neurodegenerative disease
- Age
- Medications
- Cocaine abuse (intranasal)
- Toxic chemical exposure
- Industrial agent
- Nutritional factors
- Radiation treatment of head and neck
- Congenital conditions
- Neoplasm or brain tumor
- Psychiatric conditions
- Endocrine disorders
- Epilepsy (olfactory aura)
- Migraine headache (olfactory aura)
- Cerebrovascular accident
- Sjögren's syndrome
- Systemic lupus erythematosus
Possible causes of taste loss:
- Oral and perioral infections
- Oral appliances
- Dental procedures
- Age
- Nutritional factors
- Tumor or lesions associated with taste
- Head trauma
- Toxic chemical exposure
- Industrial agent exposure
- Psychiatric conditions
- Epilepsy (gustatory aura)
- Migraine headache (gustatory aura)
- Sjögren's syndrome
- Multiple sclerosis
- Endocrine disorders
Selected medications that reportedly alter smell and taste:
- Antibiotics: ampicillin, azithromycin (Zithromax), ciprofloxacin (Cipro), clarithromycin (Biaxin), griseofulvin (Grisactin), metronidazole (Flagyl), ofloxacin (Floxin), tetracycline
- Anticonvulsants: carbamazepine (Tegretol), phenytoin (Dilantin)
- Antidepressants: amitriptyline (Elavil), clomipramine (Anafranil), desipramine (Norpramin), doxepin (Sinequan), imipramine (Tofranil), nortriptyline (Pamelor)
- Antihistamines and decongestants: chlorpheniramine, loratadine (Claritin), pseudoephedrine
- Antihypertensives and cardiac medications: acetazolamide (Diamox), amiloride (Midamor), betaxolol (Betoptic), captopril (Capoten), diltiazem (Cardizem), enalapril (Vasotec), hydrochlorothiazide (Esidrix) and combinations, nifedipine (Procardia), nitroglycerin, propranolol (Inderal), spironolactone (Aldactone)
- Anti-inflammatory agents: auranofin (Ridaura), colchicine, dexamethasone (Decadron), gold (Myochrysine), hydrocortisone, penicillamine (Cuprimine)
- Antimanic drug: lithium
- Antineoplastics: cisplatin (Platinol), doxorubicin (Adriamycin), methotrexate (Rheumatrex), vincristine (Oncovin)
- Antiparkinsonian agents: levodopa (Larodopa; with carbidopa: Sinemet)
- Antipsychotics: clozapine (Clozaril), trifluoperazine (Stelazine)
- Antithyroid agents: methimazole (Tapazole), propylthiouracil
- Lipid-lowering agents: fluvastatin (Lescol), lovastatin (Mevacor), pravastatin (Pravachol)
- Muscle relaxants: baclofen (Lioresal), dantrolene (Dantrium)

RISK FACTORS

N/A

LABORATORY

Hematocrit
Hemoglobin
White blood cell count
Blood urea nitrogen
Blood glucose
Creatinine
Blood glucose
Bilirubin
Alkaline phosphatase
Prothrombin time
Erythrocyte sedimentation rate
Altered thyroid function tests
Eosinophil count
Immunoglobulin E

Drugs that may alter lab results: N/A
Disorders that may alter lab results: N/A

PATHOLOGICAL FINDINGS

N/A

SPECIAL TESTS

Olfactory tests:
- Smell identification test - evaluates the ability to identify 40 microencapsulated "scratch and sniff" odorants
- Three-item forced-choice microencapsulated Pocket Smell Test
- Brief smell identification test
- Squeeze-bottle odor threshold test kit
Taste tests (more difficult because no convenient standardized tests are presently available):
- Research centers often use four ready-made solutions containing sucrose (sweet), sodium chloride (salty), quinine (bitter) and citric acid (sour) to obtain information about taste discrimination

IMAGING

Plain radiographs have substantial limitations; rarely useful
CT scanning is the most useful and cost-effective technique for assessing sinonasal tract inflammatory disorders and is superior to MRI in evaluation of bony structures (e.g., ethmoid, cribriform plate, olfactory cleft). Coronal CT scans are particularly valuable in assessing paranasal anatomy.
MRI useful in defining soft tissue disease; therefore, it is technique of choice to image the olfactory bulbs, tracts, and cortical parenchyma
Positron emission tomography (PET), single photon emission computed tomography (SPECT) and functional MRI (fMRI) have limited usefulness outside of research institutions. However, they have proven their usefulness in related neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and help to define neuroanatomic correlates of function.

DIAGNOSTIC PROCEDURES

Medical history
Physical examination

APPROPRIATE HEALTH CARE

Outpatient usually

GENERAL MEASURES

Appropriate treatment for underlying cause
Quit smoking
Some drug-related dysgeusias can be reversed with cessation of the offending agent

SURGICAL MEASURES

If needed for treatment of underlying cause

ACTIVITY

N/A

DIET

Patients should be cautioned not to overindulge as compensation for the bland taste of food. For example, patients with diabetes may need help in avoiding excessive sugar intake as an inappropriate way of improving food taste.
Patients with chemosensory impairment should use measuring devices when cooking, not "cook by taste"
Optimizing food texture, aroma, temperature and color may improve the overall food experience when taste is limited

PATIENT EDUCATION

Patients with permanent smell dysfunction need to develop adaptive strategies for dealing with personal hygiene, appetite, safety and health

PREVENTION/AVOIDANCE

Avoid exposures to chemicals, smoke, and radiation
Maintain good oral and nasal health with routine visits to the dentist
Eat a well-balanced diet for optimal nutrition

POSSIBLE COMPLICATIONS

Permanent loss of ability to smell or taste

EXPECTED COURSE AND PROGNOSIS

In general, the olfactory system regenerates poorly after a head injury. Most patients who recover smell function subsequent to head trauma do so within 12 weeks of injury.
Patients who quit smoking typically have improved olfactory function and flavor sensation over time
Many taste disorders (dysgeusias) resolve spontaneously within a few years of onset
Conditions such as radiation-induced xerostomia and Bell's palsy generally improve over time

ASSOCIATED CONDITIONS

Smell and taste disturbances are primarily symptoms; it is essential to look for possible underlying cause

AGE-RELATED FACTORS

Pediatric: Delayed puberty in association with anosmia (with or without midline craniofacial abnormalities, deafness, and renal abnormalities) suggests the possibility of Kallmann's syndrome
Geriatric: Aging is a cause of smell and taste deficits, but should be considered a diagnosis of exclusion
Others: N/A

PREGNANCY

Uncommon cause for smell disturbance. Many women report increased sensitivity to odors during pregnancy.

OTHER NOTES

N/A

ABBREVIATIONS

N/A

Clinical Investigations

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