Anosmia: Symptoms, Diagnosis, and Treatment

Anosmia refers to the complete inability to perceive smells. This may be noted markedly as a decreased ability to perceive flavour in food because the sense of smell is closely tied to the perception of taste as well. In a survey conducted among Americans, about 10% reported their sense of smell being affected to some degree. Anosmia has been found to affect 3% of the population over 40 years of age. The incidence increases further with increasing age reaching 11 to 25% among those between 60 to 69 years.

We are able to perceive smell through the olfactory system. The sensory nerves are located in the lining of the nose to receive the stimulus of smell from the environment. This information is transmitted via the olfactory nerves to the brain for processing. Damage to the nose, its lining, the nerves sensing and carrying the stimulus and the brain can all affect the sense of smell.

Causes of Anosmia

There are various different causes of anosmia. These are as follows:

• Damage to the nasal lining
  • Allergic Rhinitis
  • Sinusitis
  • Common cold
  • Influenza
• Obstruction of the Nasal passage
  • Nasal polyps
  • Tumor in the nasal cavity
  • Septal deviation nor other structural abnormality in the nose
• Neurological Abnormalities affecting the nerves and the brain
  • Trauma to the nose and face disrupting the nerves
  • Head trauma damaging the brain
  • Brain surgery
  • Brain tumor
  • Diabetic neuropathy affecting the olfactory nerves
  • Alzeimer Disease
  • Ageing
  • Multiple Sclerosis
  • Malnutrition
  • Heavy metal poisnoning
• Congenital Disorders (disorders present from birth)
  • Kallmann syndrome: This is a rare disease with a defect in the development of olfactory nerves. It is associated with developmental defects in various other structures including the hypothalamus(a gland in the brain) leading to decreased production of the sex hormones.

Symptoms of Anosmia

• Inability to sense any odors
• Perception of food lacking taste and flavour
• Symptoms of the causative disease (congestion, headache, running nose etc.)

Diagnosis of Anosmia

The diagnosis is made clinically from the history of poor sense of smell along with a clinical exam of the nasal passage.

• Physical examination: The nasal cavity is examined thoroughly to look at the structure and identify the presence of inflammation or blockage. The sense of smell is examined by asking the individual to identify several common odors while blindfolded.
• Laboratory investigations: blood tests to look for vitamin deficiencies, blood sugar levels are performed to screen for illness
• Imaging: Scans of the head and brain using CT or MRI are performed to look for any structural defects, tumors or neurological disease and trauma.

Treatment  of Anosmia

The treatment depends on the underlying illness

• For Inflammatory conditions affecting the lining of the nasal cavity
  • Decongestants
  • Nasal steroids
  • Saline drops
• For nasal cavity obstruction
  • Polypectomy for nasal polyps
  • Rhinoplasty to correct nasal septum deviation and other structural defects
  • Surgery to remove tumors
• For Neurological conditions
  • Treatment of damaged nerves is no possible in most cases. A slow regeneration of the nerves may occur over a long period of time.

References

1. Mann NM, et al. Anatomy and etiology of taste and smell disorders. Accessed April 9, 2019.
2. Mann NM, et al. Evaluation and treatment of taste and smell disorders. Accessed April 9, 2019, 2016.
3. Smell Disorders. National Institute of Deafness and other Communication Disorders. Accessed April 9, 2019