BASICS
DESCRIPTION
- Anosmia is defined as the inability to detect odors. This can be temporary or permanent depending on the underlying pathology.
- The sense of smell is necessary in determining the flavor of foods and beverages. It also aids in the detection of environmental hazards such as spoiled food, leaking natural gas, smoke, or airborne pollutants.
- The human sense of smell is mediated by both cranial nerve I (CN I; olfactory nerve) and by cranial nerve V (CN V; trigeminal nerve).
- Qualitative odor sensations (e.g., the smell of a flower or of spoiled food) are mediated by CN I.
- The somatosensory components of odorants (e.g., warmth, coolness, sharpness, and irritation) are mediated by the ophthalmic and maxillary divisions of CN V.
EPIDEMIOLOGY
Incidence
There are >200,000 physician visits each year for chemosensory complaints. á
Prevalence
- Prevalent sex: male > female
- Age-related deficits in olfaction are well documented (1), and the ability to detect odors slowly declines with age:
- 1-2% in people <50 years
- 24.5% in people 50 to 80 years
- 62.5% in people >80 years
ETIOLOGY AND PATHOPHYSIOLOGY
- Olfactory decline associated with aging (presbyosmia) is the most common cause of anosmia. (1).
- Anosmia not associated with presbyosmia is most often caused by nasal/sinus disease, upper respiratory infection (URI), and head trauma.
- Conductive defects
- Obstruction in the nasal cavity, caused by masses, may prevent flow of odorants to the olfactory epithelium:
- Nasal polyps (most common)
- Sinonasal papillomas
- Certain developmental abnormalities (e.g., encephaloceles, dermoid cysts) may also cause obstruction.
- Malignancy
- In addition, patients with laryngectomies or tracheotomies sometimes experience hyposmia because of a reduced or absent nasal airflow.
- Central and sensorineural defects
- Most olfactory defects are caused by inflammatory processes in the nasal cavity.
- Chronic or acute rhinosinusitis (allergic, infectious, or toxic secondary to noxious stimuli) can lead to progressive damage of the olfactory mucosa, leading to a permanent decline in olfaction.
- Viral infections
- Sarcoidosis (affecting neural structures)
- Granulomatosis with polyangiitis (Wegener granulomatosis)
- Multiple sclerosis
- Genetic causes (e.g., Kallmann syndrome)
- Endocrine disorders
- Hypothyroidism
- Hypoadrenalism
- Diabetes mellitus
- Head trauma, stroke, brain surgery, or subarachnoid hemorrhage
- Damage to olfactory bulbs or cortical lesions at the olfactory-related brain regions (e.g., amygdala, temporal lobe region, frontal lobe region) can lead to posttraumatic anosmia.
- Iatrogenic: toxicity from systemic or inhaled drugs (e.g., aminoglycosides, formaldehyde, alcohol, nicotine, organic solvents, zinc nasal sprays)
- Degenerative processes of the central nervous system (CNS) (2)
- Parkinson disease
- Alzheimer disease
- Normal aging, also known as presbyosmia
Genetics
Anosmia may present as a symptom in some genetically associated disorders (Kallmann syndrome, migraine syndromes, rheumatologic conditions, endocrine disorders, and Alzheimer disease). á
RISK FACTORS
- Age >65 years
- Poor nutrition
- Smoking tobacco
GENERAL PREVENTION
- Smoking cessation
- Good oral hygiene and avoidance of noxious chemicals
- Following a well-balanced diet
COMMONLY ASSOCIATED CONDITIONS
Chronic rhinosinusitis, URIs, migraines, and head trauma á
DIAGNOSIS
HISTORY
- History of present illness should investigate the time course of symptoms and their relation to any URI or head injury. Important associated symptoms include nasal congestion, rhinorrhea, or both. Also, the nature of rhinorrhea should be assessed (e.g., watery, mucoid, purulent, or bloody).
- Review of systems should assess neurologic symptoms, particularly those involving mental status (e.g., difficulty with recent memory) and cranial nerves (e.g., diplopia, difficulty speaking or swallowing, tinnitus, and vertigo).
- Past medical history should inquire about sinus disorders, cranial trauma or surgery, allergies, drugs used, and exposure to chemicals or fumes.
PHYSICAL EXAM
- The nasal passages should be inspected thoroughly for swelling, inflammation, discharge, and polyps. To help identify obstruction, have the patient breathe through each nostril sequentially (while the other is manually occluded).
- A complete neurologic examination, particularly of mental status and cranial nerves, should also be done.
DIAGNOSTIC TESTS & INTERPRETATION
Olfactory tests are available to evaluate olfactory function: á
- Pungent odors such as from vials containing coffee, cinnamon, or tobacco are placed under the open nostril while the other nostril is manually occluded. If the patient can identify the substance, olfaction is presumed to be intact. The test is repeated on the contralateral nostril to determine whether the response is bilateral. Unfortunately, this method of testing is crude and often unreliable.
- The most widely used quantitative clinical test is the University of Pennsylvania Smell Identification Test (UPSIT). This test is also known as the smell identification test. The UPSIT test consists of four booklets containing 10 microencapsulated odors in a "scratch-and-sniff"Ł format. There are four response alternatives accompanying each odor. The patient is asked to identify (or guess) each smell. The test can be self-administrated in the waiting room or in the patient's home and can be scored in <1 minute by nonmedical personnel. Scores are compared with varying patient groups and compared against sex- and age-related norms. The patient's score is then classified into one of the following categories: normosmia, mild microsmia, moderate microsmia, severe microsmia, anosmia, and probable malingering. The reliability of this test is very high.
Initial Tests (lab, imaging)
- Laboratory testing is dictated by history and physical exam. (3)[C]
- CBC
- Basic metabolic panel (BMP)
- TSH
- HbA1C
- ESR, RF, ANA (rheumatologic concerns)
- Antineutrophil cytoplasmic antibody (ANCA) (granulomatosis with polyangiitis)
- IgE (allergies)
- Testosterone (for males), estrogen (for females), LH/FSH (if Kallmann syndrome suspected)
- Radiographic studies should be reserved for specific indications.
- A CT scan is considered the ideal investigation for evaluating nasal or sinus dysfunction. It provides detailed information on mucosal disease, structural abnormalities, and the presence of sinusitis or a neoplastic process.
- MRI is superior to CT for the identification of intracranial pathology. It is the study of choice to evaluate the olfactory bulbs and tracts as well as other intracranial causes of olfactory dysfunction.
TREATMENT
Treatment depends upon the underlying pathology: á
- Elimination of toxins (tobacco, household cleaning chemicals) (3)[C]
- Sinus conditions should be managed initially with saline lavage, decongestants, antihistamines, antibiotics, and nasal or systemic steroids as indicated. (1)[C],(3).
- Surgical intervention should be considered with polyps and sinus disease that are resistant to medical management (1)[C].
- Intranasal corticosteroids for causes associated with inflammatory processes in the nasal cavity (i.e., rhinosinusitis with allergic etiology)
- Address any underlying endocrine disturbances (hypothyroidism, diabetes) (1)[C],(3,4).
ADDITIONAL THERAPIES
- ENT or neurology referral for recalcitrant anosmia
- Surgical referral for obstructive etiologies (polyps, papillomas)
ONGOING CARE
PATIENT EDUCATION
- Counsel patients on safety issues that may arise from the inability to detect odors. These include reading expiration dates on foods, ensuring household smoke detectors are functional, limiting exposure to toxic chemicals, and exercising caution when using gas heating/cooking. (4)[C].
- Nutrition is another aspect for which patients will have to develop coping strategies for, as the sense of smell markedly impacts the sense of taste.
- Patients will also need to be more cognizant of hygiene and health issues.
PROGNOSIS
- Olfactory dysfunction related to sinus infection and inflammation responds according to the severity of the underlying disease (1)[C].
- Chronic sinus infections may progressively lead to destruction of the olfactory mucosa and a permanent, irreversible decline in olfaction. (4).
- Anosmia secondary to head trauma is usually permanent depending on the severity of damage to the underlying olifactory parenchyma (4).
COMPLICATIONS
- Permanent loss of smell.
- Secondary risks such as illness due to eating spoiled food or inhaling smoke and/or noxious fumes
REFERENCES
11 Pinto áJM. Olfaction. Proc Am Thorac Soc. 2011;8(1):46-52.22 Godoy áMD, Voegels áRL, Pinna Fde áR, et al. Olfaction in neurologic and neurodegenerative diseases: a literature review. Int Arch Otorhinolaryngol. 2015;19(2):176-179.33 Bromley áSM. Smell and taste disorders: a primary care approach. Am Fam Physician. 2000;61(2):427-436, 438.44 Fried áMP. Approach to the patient with nasal and pharyngeal symptoms. In: The Merck Manual for Health Care Professionals. http://www.merckmanuals.com/professional/ear_nose_and_throat_disorders/approach_to_the_patient_with_nasal_and_pharyngeal_symptoms/anosmia.html. Accessed 2015.
ADDITIONAL READING
- S ínchez-Vallecillo áMV, Fraire áME, Baena-Cagnani áC, et al. Olfactory dysfunction in patients with chronic rhinosinusitis. Int J Otolaryngol. 2012;2012:327206.
CODES
ICD10
- R43.0 Anosmia
- J39.8 Other specified diseases of upper respiratory tract
ICD9
- 781.1 Disturbances of sensation of smell and taste
- 951.8 Injury to other specified cranial nerves
- 478.9 Other and unspecified diseases of upper respiratory tract
SNOMED
- Loss of sense of smell (finding)
- Traumatic anosmia (disorder)
CLINICAL PEARLS
- Advancing age is the greatest risk factor associated with a decline in olfaction; however, this is a diagnosis of exclusion and other causes must be ruled out. (3)
- Red flags include previous head injury, neurologic signs/symptoms, and sudden onset (3).
- Timing is an important clue: Sudden loss of smell is strongly indicative of trauma or cerebrovascular accident (CVA); gradual loss is indicative of polyps/growths or chronic infection; while intermittent losses are suggestive of inflammatory etiologies (e.g., seasonal allergic rhinitis [SAR]) (3).
- Cranial imaging is not generally part of the initial workup unless stroke/head trauma is suspected, or there is sudden anosmia with no clear inciting etiology. (4).