Loss of sensation of smell is the main clinical presentation of anosmia. In addition, individuals may also experience symptoms associated with underlying conditions causing anosmia. Individuals with anosmia also experience loss of appetite. This is so because, 80% of the flavors of food comes through sensation of smell [6]. Affected individuals also suffer from depression and isolation because they are devoid of some of the basic pleasures of life such as smelling a flower, scent of a loved one and or fragrance of perfume [7].

• Inflammation

  When the sense of smell gradually disappears over time, the more likely cause is sinus inflammation, chronic obstruction from infection or allergy, or a progressive disease such as AD. [uspharmacist.com]

  After looking for the cause, your ENT specialist may decide to treat a nasal inflammation or obstruction. This may involve topical and/or oral medications to reduce inflammation, antibiotics, or surgery inside the nose. [med.uth.edu]

  Corticosteroids — Cortisone, prednisone, and related drugs that reduce inflammation. Nasal polyps — Drop-shaped overgrowths of the nasal membranes. [medical-dictionary.thefreedictionary.com]

• Malnutrition

  Loss of smell can: Reduce or eliminate the enjoyment of food Disable the detection of dangerous odors/spoiled food Cause a loss interest in eating, which can lead to weight loss, malnutrition and depression Beyond these lifestyle changes, anosmia can [nyogmd.com]

  The sense of smell is important to overall health and nutrition since diminished sensations can lead to poor appetite and malnutrition, especially in the elderly. An altered sense of smell may pose other health-related problems. [yalemedicine.org]

  However, losing the sense of smell can also mean losing interest in food, provided that in the long term it can lead to weight loss, malnutrition or depression. [humanitas.net]

• Epilepsy

  A large number of neurological conditions can cause disturbances in the sense of smell, including epilepsy (particularly temporal lobe epilepsy), multiple sclerosis, and previous strokes. [bjgp.org]

  […] olfactory dysfunction: direct viral damage to neuroepithelium § 5% head trauma patients have anosmia due to shearing across cribriform plate § manipulation of septum and osteotomies may cause shearing of olfactory nerves OTHER CAUSES: § Neurologic: MS, epilepsy [enotes.tripod.com]

  […] this damage, including: old age Alzheimer’s disease brain tumors Huntington’s disease hormonal problems underactive thyroid medications, including some antibiotics and high blood pressure medications multiple sclerosis Parkinson’s disease schizophrenia epilepsy [healthline.com]

  […] traumatic olfactory dysfunction resolve, with the majority within 12 weeks medication related (for example, ACE inhibitors, diuretics, calcium channel blockers, statins, tobacco alcohol and illicit drug (especially cocaine) abuse neurological (temporal lobe epilepsy [gpnotebook.com]

• Weakness

  The following findings are of particular concern: Recent head injury Symptoms of nervous system dysfunction, such as weakness, trouble with balance, or difficulty seeing, speaking, or swallowing Sudden start of symptoms Local or global outbreak of COVID [merckmanuals.com]

  mild weakness of other muscles), 7 were Class III (eye muscle weakness of any severity, moderate weakness of other muscles), and 3 were Class IV (eye muscle weakness of any severity, severe weakness of other muscles). [doi.org]

• Hyposmia

  Hyposmia is more often present and typically more severe in PD patients than other parkinsonian syndromes, making it a potentially useful biomarker for the disease. © 2017 Elsevier Inc. All rights reserved. [ncbi.nlm.nih.gov]

  This is then called Hyposmia. Hyposmia is the reduced ability to detect odors. Usually a loss or diminished sense of smell is often accompanied by a loss or diminished sense of taste. The sense of taste is actually derived from your sense of smell. [sinuswars.com]

  ‘During examination, the subjects were asked about known anosmia or hyposmia.’ [en.oxforddictionaries.com]

• Dysgeusia

  Associated medical events accompanying anosmia included dysgeusia, cerebrospinal fluid leaks, and meningitis. [ncbi.nlm.nih.gov]

  How soon after did the anosmia/dysgeusia resolve? * [entnet.org]

  Anosmia is loss of a sense of smell Hyposmia is reduced ability to smell Dysgeusia is altered sense of taste Losing your sense of smell does not automatically mean that you have COVID-19. [ems1.com]

• Muscle Weakness

  mild weakness of other muscles), 7 were Class III (eye muscle weakness of any severity, moderate weakness of other muscles), and 3 were Class IV (eye muscle weakness of any severity, severe weakness of other muscles). [doi.org]

  Go to the emergency room if you lose your sense of smell and experience neurological symptoms such as dizziness, slurred speech or muscle weakness. [verywellhealth.com]

  Myotoxicity — defined by local or generalised myalgia and/or muscle weakness in association with a serum creatine kinase (CK) level > 1000 U/L. [mja.com.au]

  weakness, hypertension, hy- pokalemia, and osteopenia. [archive.org]

• Cryptorchidism

  Can be associated with other abnormalities such as cryptorchidism, midline craniofacial defects, deafness, and renal agenesis. Important to rule out other causes of anosmia which may have occurred in infancy and childhood. [anosmiafoundation.com]

• Confusion

  Progressive confusion and recent memory loss in an elderly patient suggest Alzheimer disease as a cause. Waxing and waning neurologic symptoms affecting multiple areas suggest a neurodegenerative disease such as multiple sclerosis. [merckmanuals.com]

  Progressive confusion and recent memory loss point to Alzheimer’s disease in the elderly. Neurodegenerative diseases such as multiple sclerosis are suspected in cases with waxing and waning neurologic symptoms. [medindia.net]

  It is sometimes confused with anosmia - a loss of the sense of smell. Often chronic sinusitis can lead to anosmia, a reduced sense of smell. [diki.pl]

  Advertisement Loss of smell is often confused with the loss of taste – known as ageusia – but the two are very different. [newscientist.com]

• Dizziness

  R41.841 Cognitive communication deficit R41.844 Frontal lobe and executive function deficit R41.89 Other symptoms and signs involving cognitive functions and awareness R41.9 Unspecified symptoms and signs involving cognitive functions and awareness R42 Dizziness [icd10data.com]

  Go to the emergency room if you lose your sense of smell and experience neurological symptoms such as dizziness, slurred speech or muscle weakness. [verywellhealth.com]

  Urinary incontinence - Urinary retention - Oliguria - Polyuria - Nocturia - Extravasation of urine - Extrarenal uremia Cognition, perception, emotional state and behaviour Anxiety - Somnolence - Coma - Amnesia (Anterograde amnesia, Retrograde amnesia) - Dizziness [chemeurope.com]

  Confusion (Delirium) · Somnolence · Obtundation · Stupor · Unconsciousness (Syncope, Coma, Persistent vegetative state) Fainting/Syncope Carotid sinus syncope • Heat syncope • Vasovagal episode Other Amnesia (Anterograde amnesia, Retrograde amnesia) · Dizziness [psychology.wikia.org]

  She denied any neurological symptoms such as headache, nausea, vomiting, dizziness, or seizures or difficulty with bowel or bladder function. [surgicalneurologyint.com]

• Neurologic Manifestation

  Manifestations Nervous System Diseases Signs and Symptoms Acetylcysteine N-monoacetylcystine Antiviral Agents Anti-Infective Agents Expectorants Respiratory System Agents Free Radical Scavengers Antioxidants Molecular Mechanisms of Pharmacological Action [clinicaltrials.gov]

  Combinations of MeSH descriptors and the Boolean operator, “AND,” were used: coronavirus infections AND olfactory disorders, coronavirus infections, and neurological manifestations. [ejnpn.springeropen.com]

  Neurological Manifestations of Hospitalized Patients with COVID-19 in Wuhan, China: a retrospective case series study. 2020. American Academy of Otolaryngology – Head and Neck Surgery. [cebm.net]

  Anosmia was reported to be a rare occurrence in SARS infection.11 In a series reported by Mao et al analyzing the neurologic manifestation of 214 COVID-19 adult patients, hypogeusia occurred in 5.6% of patients, whereas 5.1% reported hyposmia.12 So far [journals.lww.com]

• Asthenia

  (Dysphasia, Aphasia, Dysarthria) - symbolic dysfunctions (Dyslexia, Alexia, Agnosia, Apraxia, Acalculia, Agraphia) - voice disturbances (Dysphonia, Aphonia) General symptoms and signs Fever (Hyperpyrexia) - Headache - Chronic pain - Malaise/Fatigue (Asthenia [chemeurope.com]

  The most prevalent symptoms were asthenia, headache, and nasal obstruction. [frontiersin.org]

• Slurred Speech

  Go to the emergency room if you lose your sense of smell and experience neurological symptoms such as dizziness, slurred speech or muscle weakness. [verywellhealth.com]

A preliminary medical history about illnesses will be gathered. Following this, a complete internal examination of the nose will be done. Blood tests would be carried out for evaluating the presence of underlying disease conditions. Imaging studies such as CT scan detect development of tumors in the olfactory system and MRI would also be required to study any anomalies of the brain. In addition, nasal endoscopy and anterior rhinoscopy will also be carried out to detect conditions of nasal polyps as well as inflammation of neuronal membrane. Neurological system examination also provides useful insight about the cranial nerves, sensorimotor functions and cerebellar functions [8].

Treatment of anosmia depends on the underlying cause of the condition. If individuals suffer from congenital anosmia, then the condition cannot be cured. This is so because, such a kind of condition is linked to genetic predisposition and treatment methods to correct the genetic defects have not yet been designed.

The other forms of anosmia can be treated to a significant extent if the underlying disease condition can be effectively managed. The following treatment methods would be of help:

• Nasal decongestant would be of help if nasal congestion is causing temporary loss of smell.
• Antistamines are prescribed when allergic reactions are the cause of anosmia.
• Vaporizer or a humidifier may be recommended to loosen the mucus.
• Surgical procedures would be required to remove the nasal polyps or to strengthen the nasal septum, if it is interfering with the sense of smell [9].
• Sinus surgery would be employed in cases, when sinusitis gets severe and dramatically affects the sense of smell [10].

Certain forms of anosmia that are induced by use of nasal decongestants or common cold infections have a good prognosis rate. However, there are cases, when complete recovery of smell sensation cannot be achieved. This so because, in cases when there are conditions of sinusitis or degenerative diseases of the brain develop, they can significantly cause nerve damage; and then recovery of sensation of smell would be a difficult affair.

The following factors give rise to the condition of anosmia:

• Several medications such as estrogen, reserpine, nasal decongestants when used for longer duration, naphazoline, amphetamines and phenothiazines significantly influence the ability to detect odors.
• Obstruction in the nasal passage due to development of polyps, nasal tumors and septal deformities in the nasal cavity [2]
• Endocrine disorders, allergic reactions and respiratory infections
• Injury or trauma to the head
• Treatment methods such as radiation therapy
• Nutritional deficiencies 
• Conditions that irritate the inner lining of the nose include allergic sinusitis, hay fever, common cold, nonallergic rhinitis and influenza [3]

Anosmia can be of various types depending on the nature of the condition. For example, many individuals develop loss of sensation of smell to one particular odor; such a condition is termed as specific anosmia. In yet another form, the sense of smell would be absent from birth, this is called congenital anosmia [4].

In UK, it has been estimated that about 6,000 individuals are born with congenital anosmia. Statistics have also revealed that, anosmia affects more than 6 million individuals of the US.

Temporary loss of smell sensation can be attributed to common cold or infections affecting the nasal cavity. Damage to the olfactory nerves contained in the nose or olfactory system can cause permanent loss of sensation of smell. Death of olfactory receptor neurons present in the nose due to brain injury or trauma can also result in development of anosmia. In individuals with congenital anosmia, there is a certain kind of genetic defect that does not activate the sense of smell at birth. It has been seen that such a type of condition is heredity in nature and runs in families.

In some cases the condition of anosmia can indicate the onset of certain degenerative diseases such as Alzheimer disease and or Parkinson's disease. Development of nasal polyps or use of nasal sprays for prolonged duration can also cause anosmia [5].

The condition of anosmia cannot be prevented. However, several steps can be taken to ensure safety of the affected individual.

• Individuals are advised to install smoke alarms in all rooms.
• Appliances that work on natural gas should be avoided.
• All foods should be marked with expiry date with special caution for leftover foods.
• All the labels on kitchen cleaners as well as pesticides should be carefully read before use.

Loss of sensation of smell is often a temporary condition that can occur during conditions of common cough and cold. Anosmia primarily occurs due to inflammation of the nasal passage which consists of the paranasal sinus lining and the superior as well as the middle turbinates. Sometimes, anosmia can indicate onset of underlying conditions such as meningitis, ciliopathy and neurosyphillis. Injury or trauma concerning the head can also lead to loss of sensation of smell [1].

Definition: Anosmia refers to loss of sensation of smell due to various factors. The condition can either be present at birth or can be acquired due to underlying disease conditions. Loss of smell can either be partial or complete in nature.

Cause: Allergies, infections, development of nasal polyps, degenerative disease of the brain, injury or trauma to the head, brain tumor, underactive thyroid, kidney or liver diseases, and certain medications can all cause anosmia.

Symptoms: Anosmia presents with loss of sensation of smell. Affected individuals also experience loss of appetite which can occur due to inability to sense the flavors of food.

Diagnosis: Diagnosis begins with a preliminary internal examination of the nose. Simultaneously blood tests are done to determine disease condition. In addition, imaging studies such as CT scan and MRI are also done. Neurological examination is also required to test for abnormalities if any.

Treatment: Treatment involves managing the underlying disease condition to restore the smell sensation. If infections or common cold is causing a stuffy nose then nasal decongestant should do the trick. If nasal polyps are the cause then surgery to remove them would be required. In many cases, surgical procedures would also be opted for straightening the nasal septum.

1. Sumner D. Post-traumatic anosmia. Brain 1964; 87:107.
2. Norlander T, Bronnegard M, Stierna P. The relationship of nasal polyps, infection, and inflammation. Am J Rhinol. Sep-oct 1999;13(5):349-55.
3. Apter AJ, Mott AE, Frank ME, Clive JM. Allergic rhinitis and olfactory loss.Ann allergy asthma immunol 1995; 75:311.
4. Smith DV, Duncan HJ. Primary olfactory disorders: anosmia, hyposmia and dysosmia. In: science of olfaction, serbymj, chobor kl (eds), springer-verlag, new york 1992. P.439.
5. Semmes J, Weinstein S, Ghent L, Tanber HL. Normative study. In: somatosensory changes after penetrating brain injuries in man, semmes j (ed), harvard university press, cambridge 1960. P.4.
6. Rusiniak KW, Hankins WG, Garcia J, Brett LP. Flavor-illness aversions: potentiation of odor by taste in rats. Behav neural biol 1979; 25:1.
7. Radenne F, Lamblin C, Vandezande LM, et al. Quality of life in nasal polyposis. J Allergy Clinimmunol. Jul 1999;104(1):79-84.
8. Andrews AE, Bryson JM, Rowe-Jones JM. Site of origin of nasal polyps: relevance to pathogenesis and management. Rhinology. Sep 2005;43(3):180-4
9. Blaiss MS. Expanding the evidence base for the medical treatment of nasal polyposis. J Allergy Clinimmunol. Dec 2005;116(6):1272-4.
10. Lund VJ. The effect of sinonasal surgery on asthma. Allergy. 1999;54 suppl 57:141-5.